A Treatise on the Plague and Yellow Fever / With an Appendix, containing histories of the plague at Athens in the time of the Peloponnesian War; at Constantinople in the time of Justinian; at London in 1665; at Marseilles in 1720

by James Tytler

SECTION III.

Of Disease in general.—The nature of the Plague as a Disease considered.—Of Contagion.—Whether the Plague is really Contagious or not.—Medical History of the Distemper.—Inquiry into its Immediate Causes, and whether an approaching Plague is indicated by any visible Signs.

HITHERTO we have considered the origin of the plague entirely in a moral point of view. We have seen, that, in conformity to the general opinion of mankind, it may reasonably be supposed to have been inflicted upon mankind, the Jews particularly, for their transgressions; that, having been once introduced, it has been perpetuated, and spread from nation to nation, and that in proportion to the degree of immorality of a certain kind prevailing through the world. From this it is naturally to be inferred, that, were the human race to live at peace with one another, to disperse themselves over the face of the earth for the purpose of improving it by cultivation, and were they to be contented with what the produce of each country affords, there would be no plague among them. But we know that such a reformation is not to be expected, and we must take the world as we find it. The question then is, By what means shall individuals secure themselves from being destroyed by a plague which shall happen to invade any country; or how shall a person, already infected with it, be restored to health? For this purpose let us begin with considering the nature of disease in general, and of the plague particularly.

As to disease in general, physicians have differed very considerably in their definitions; and, though many have been given, few seem to be unexceptionable. That of Dr. Fordyce seems to be among the clearest and most expressive. “Disease (says he) is such an alteration in the chemical properties of the fluids or solids, or of their organization, or of the action of the moving powers, as produces an inability or difficulty of performing the functions of the whole or any part of the system, or pain, or preternatural evacuation.” But as this definition, however just, cannot be easily understood by such as are unaccustomed to medical language, I shall attempt the following explanation of the animal economy, and the diseases to which it is subject.

1. By nature our bodies are formed of certain solid and fluid parts, operating upon one another in a manner of which we know but little. Anatomists have described the structure of the human body and its parts in a certain degree, but have always found themselves lost in an inconceivable minuteness of texture. The whole structure of the human body, visible and invisible, is called its ORGANIZATION.

2. This organized body is acted upon by certain powers residing in the atmosphere, by which it becomes endowed with LIFE.

3. The operation of those powers upon a well organized body constitutes that agreeable and vigorous state which we call HEALTH.

4. The operation of any other power, substituted in place of the natural one, even upon a body perfectly organized, produces a state very different from health; commonly attended with some uneasy sensations, and which is called DISEASE. I say it is commonly attended with uneasiness, but not always; for many persons within a few hours, nay, a few minutes, of their death, have imagined themselves quite recovered and well. To illustrate the meaning of what is said of the substitution of any power instead of the natural one: It is natural for man to breathe air of a certain quality; and while he does so he continues in health; but let him breathe the vapour of burning charcoal, or of fermenting liquor, mixed in considerable quantity with the air to which he has been accustomed, and he will very soon find himself diseased. Many other kinds of elastic fluids may be substituted instead of the vapour just mentioned, all of which will in a short time produce a disease in the most healthy man. The state of a diseased body being very different from that of a sound one, the appearances are consequently very different. The various appearances of disease in the human body are called symptoms of that disease, from a Greek word signifying appearance.[44]

5. A disease proves mortal only by the DISORGANIZATION of the body. By disorganization I mean any considerable alteration in the structure of the body, visible or invisible. The truth of this will appear from a consideration of the method by which animals may be recovered, after being to appearance dead by breathing the vapour of charcoal, or fixed air in any other form, viz. by plunging them in cold water. In a cave in Italy a continual stream of this kind of air issues from the ground. It rises but a small way, so that a man may safely enter, because his head is above the vapour; but, if he brings a small dog with him, the animal, in consequence of breathing the pernicious fluid, falls down as if dead, and would very soon die if left there. By throwing it into a lake in the neighbourhood, (cold water of any kind would answer as well) it recovers. In the dissection of some unfortunate people, who have been killed by breathing this pernicious fume, a manifest disorganization has been observed, viz. a rarefaction of the blood, and too great dilation, or even rupture, of the small vessels.

6. A disease cannot always be cured by removing the cause which brought it on: it is necessary also to repair the injury done to the organization. This is exemplified in the case of the dog just mentioned. Taking him out of the vapour is not sufficient for his recovery, because the organization of the body is injured; the cold water by contracting the vessels repairs the injury, and the cure is completed. To the entire preservation of this organization it is probably owing, that people have frequently recovered after being thought dead for a long time.[45]

7. When the organization of the body is injured, the action of the natural powers themselves occasions uneasiness, and increases the disease. The cure then is, to substitute instead of the natural power, as far as possible, the action of some other power till the organization is restored; after which the natural power must be again allowed to act, or a disease of another kind will take place. This may be exemplified in a consumption of the lungs; where, that part being very much disorganized, pure air renders the disease worse; and the sick are relieved by mixing with the common atmosphere such kinds of air or vapour as would prove pernicious to people in health. But, supposing this method to be successful, and the consumption to be entirely removed, it is plain that the use of the pure atmosphere must be resumed, or the impure air would bring on a disease in the same manner as on a healthy person.

8. The body is wasted in the natural operations of life; part of it passing off with the vapour of the breath, part by insensible perspiration, &c. Hence it naturally tends to disorganization and death, unless the waste be repaired.

9. This natural waste of the body is repaired, and health kept up, by the food and drink taken into the stomach.

10. Hence arises another set of diseases; for as the reparation of the waste, just mentioned, depends on the proper action of the stomach upon the food, and the assimilation of the latter with the substance of the body, it is plain that this operation depends both on the proper quality of the food, and the sound state of the stomach itself.

11. The body is composed of solids and fluids of different kinds, every one of which is subject to diseases peculiar to itself; but, by reason of the connexion of the parts of the body with one another, it is impossible that any one can be very much disordered without affecting all the rest. As the bond of connexion, however, is in many cases totally invisible to us, surprising instances frequently occur of one part being affected in consequence of an injury done to another very distant from it. This connexion between all parts of the body is called SYMPATHY. Dr. Gardiner of Edinburgh, in his observations on the animal economy, &c. says, that “the stomach is the principal seat of many of the most remarkable sympathetic affections which happen in valetudinary states of the body. Every disorder accompanied with severe pain affects the stomach, whilst this viscus affects not only in its diseased state every part of the system, but at other times the effects of healthful stimuli applied to it are instantly communicated to the rest of the body, as when we take food, wine, or medicine.” Dr. Darwin in his Zoonomia informs us that the stomach is said to sympathize with almost every part of the body; but Dr. Moore, in his medical sketches, tells us that the heart possesses a greater share of sympathy than any other part in the body, and next to it the stomach.[46]

12. The solid parts of the body are the bones, the muscles, brain and nerves; the fluids are, the blood, and others produced from it. The bones are known to every one; the muscles are the fleshy parts throughout the whole body; and the nerves are a kind of cords seemingly originating from the brain, and from thence accompanying the blood vessels through all parts of the body.

13. Much has been disputed about what is to be accounted the primary part of the body, on which all the rest depend; and one class of disputants have arranged themselves on the side of the blood, and the other on that of the nerves. The dispute is like one about the beginning of a circle. It cannot be decided, because the blood cannot act without nerves, nor the nerves without blood. I speak of the human body, being aware that in some animals the position may be controverted. The following is a concise state of the matter.

14. All the blood in the body passes through the heart; which has four cavities; two called ventricles, and two auricles. These, from their position in the body, are called the right and left. The right ventricle communicates with the right auricle, as does also the left ventricle with the left auricle; but there is no communication between the right ventricle and the left, nor between the right auricle and the left. Through these cavities all the blood passes to every part of the body, and returns from every part; but, as in the former case, we are here at a great loss where to begin its motion; for this is precisely to find the beginning of a circle. As we must begin somewhere, however, we shall do so with the right ventricle of the heart. This receives the blood returning from all parts of the body, and propels it into the right ventricle; not the whole quantity at once, for it cannot contain one half of it; but by degrees. The auricle contracts as soon as it is full; and in the time that the auricle fills, the ventricle contracts, so that it may be empty, and ready to receive the blood from the auricle. By the contraction of the right ventricle the blood is driven into the pulmonary artery, and passes into the lungs. Here the artery branches into an infinite number of small vessels much finer than hairs; and these again, uniting into larger trunks, form at last the pulmonary vein, which brings back the blood to the heart. The pulmonary vein is inserted into the left auricle of the heart, which, as soon as it is filled with blood, contracts, and expels the blood from it into the left ventricle. From the left ventricle issues a large artery called the aorta, which by its branches supplies the whole body with the vital fluid. In all parts of the body the arteries divide themselves into innumerable small branches, which terminate in veins equally small as in the lungs; but it has been disputed whether the arteries and veins actually join each other in the form of vessels, or whether the arteries deposit the blood in small cells, from which the veins suck it up. The dispute is of no consequence, nor can it be absolutely decided, on account of the exceeding smallness of the vessels; though the microscopical observations are rather favourable to the opinion of a continuation of vessels. The veins from all parts of the body unite into larger vessels, and these again uniting with one another, form at last one very large vein called the vena cava, which opens into the right auricle of the heart, from which the circulation goes on as already described. The two ventricles of the heart, and all the veins throughout the body, are furnished with a kind of valves, which allow the blood to proceed in the way of circulation, but prevent its returning in a contrary direction.

15. The lungs, through which all the blood in the body passes, receive likewise the air which we draw in every time we breathe. They consist of two large bodies called lobes; from their situation called the right and left. The air is conveyed into them by the wind-pipe, called also the trachea, and the aspera arteria. On entering the cavity of the breast, the wind-pipe divides into two large branches called the bronchiæ; one of which goes to the right and the other to the left lobe of the lungs. By the further division and subdivision of these vessels the lungs are filled with an innumerable multitude of little tubes, terminating in exceedingly minute bladders or cells, which are the final receptacles of the air sucked in when we breathe. Each of these cells is surrounded with a kind of network of blood-vessels exceedingly small, and consisting of very thin membranes; so that, in passing through the lungs, the blood is exposed as much as possible to the action of the air.

16. It is a matter of great importance to find out what is the use of this exposure of the blood; and great disputes have taken place concerning it. In former times it was supposed that the blood received from the air a vital spirit, without which it would have been totally incapable of performing its offices in the body. Later physiologists endeavoured to explode this notion. Dr. Hales particularly, by shewing that the circulation of the blood through the lungs might be continued by inflating and contracting them alternately by the fumes of burning brimstone, endeavoured to prove that the use of the air was only to give the lungs an opportunity of dilating and contracting alternately, by which means principally he thought the circulation might be carried on. This continued to be the most common hypothesis as late as the time of Dr. Huxham. It was however thought also that by the compression of the air the blood was altered in its texture, its bulk, &c. Accordingly Dr. Huxham tells us in the preface to his treatise on air and epidemic diseases, that “air fit for respiration ought neither to be too hot, nor very cold; for the use of the inspired air is to temperate the blood, which would otherwise grow too hot, and putrefy, as is evident from the experiment of the most excellent Boerhaave made in a hot house; for, if the air is more hot, or even equally hot, as the blood of any animal, it certainly soon dies.”[47]

17. The modern discoveries in the composition of air, have tended greatly to elucidate the use of this fluid in the lungs, and its action on the blood in respiration. Dr. Priestly first determined it to be what he terms a phlogistic process, i. e. a process by which the parts of the blood no longer proper to be retained among the rest, or at least some of them, are carried off. That something is carried off either from the lungs themselves, or from the blood circulating through them, is evident; for the air which is taken into the lungs in a dry state, comes out of them extremely moist, and loaded with vapour. An essential change is also made in the nature of the air itself; for it now assumes in a great measure the nature of what has been called fixed air, or the fume of charcoal, or fermenting liquor, and thus becomes unfit for being breathed a second time. This change is made by the addition of some terrestrial substance to the pure atmosphere, which the latter volatilizes and carries along with it.[48]

18. But, whatever may be carried off from the blood, during its passage through the lungs, something is certainly added to it, for the blood in the pulmonary artery is of a dark red, but when it has undergone the action of the air in the lungs, and returns by the pulmonary vein, it is then of a bright scarlet, which colour it retains through all the arteries of the body, but loses it on its return through the veins. This scarlet colour is communicated to blood in all cases when exposed to the air; and Dr. Priestley has observed that it is acted upon by the air even through a bladder; much more then must it be so through those very thin membranes which form the coats of the fine pulmonary vessels. What this subtile matter is which the blood receives, shall be afterwards inquired into; at present it is sufficient to take notice that it is absolutely necessary, for the purposes of life, that the blood should pass through the lungs: for, as Dr. Huxham observes, “we see neither nutrition, nor the motion of the muscles, performed by any blood that hath not passed through the lungs; this is observable from the coronary arteries[49] to the ultimate ramifications of the aorta.” As the previous circulation of the blood through the lungs therefore is absolutely necessary to the growth and life of the body, and as the blood certainly receives something from the air, we must account this a proof, and no inconsiderable one, that the air contains a vital spirit, which it imparts to the blood in the lungs. But, before we proceed farther on this subject, it is proper to take some notice of

19. The nerves. These, which constitute such a remarkable and important part of the human body, are white cords, of a soft pulpy substance, defended by a tough skin which goes along with them as far as they can be traced. All the nerves either originate from the brain, or terminate in it. The former doctrine hath been generally adopted, and in conformity to that doctrine the following account of the nerves is laid down. The brain is enclosed in the cavity of the scull, but not without the intervention of two membranes, called the dura and pia mater, to prevent injury from the hard bones, as well as for other purposes. The brain is divided into two lobes, the right and left. It is composed of two different kinds of substance, the outermost called the cortical, the innermost the medullary substance; the latter seems composed of fine fibres. The whole of the medullary part of the brain terminates in a substance called the cerebellum, very much resembling the brain, but smaller. The cerebellum terminates in another substance resembling the medullary part of the brain, called the medulla oblongata. The cerebellum lies in the back part of the head, and the medulla oblongata under it. The latter terminates in the spinal marrow, extending from the lower and back part of the head to the lower extremity of the back bone, and is enclosed in the hollow of that bone. The nerves proceed from these four substances, viz. the brain, the cerebellum, the medulla oblongata, and spinal marrow. As they pass to all parts of the body they accompany the arteries, dividing with them into innumerable small branches; but they do not return with the veins; so that they seem not to contain any fluid which goes and comes, or which circulates like the blood. The nervous fluid, if any such there be, seems to move constantly one way, either to the brain or from it.

20. Hitherto we have noticed only things which are evident to our senses, and which the industry of anatomists has abundantly evinced; but now our subject renders it necessary to step aside a little into the obscure regions of theory and conjecture. The muscles, as we have formerly said, are the fleshy parts of the body; and by them all the motions of the body are performed. The flesh is distributed into distinct portions, each of which is enclosed in a membrane belonging to itself. Each of these portions is a muscle, and each muscle has a branch of an artery and the branch of a nerve belonging to it. On both these the action of the muscle depends; for, if we cut the nerve belonging to a muscle, it immediately loses all power of action; and if we cut the artery which accompanies the nerve, it does the same. As therefore the blood is found to receive something from the air, and as it loses this when passing through the arteries, and as the nerves lose their power when the communication with the blood is cut off, it seems extremely probable, that what is imbibed by the blood in the lungs is taken up by the fine ramifications of the nerves, and is no other than the immediate principle of life and sensation. Thus we will establish a doctrine directly opposite to that commonly received; for, instead of supposing that the nerves originate from the brain, we are now led to suppose that they terminate in it. Instead of supposing that the sensations originate in the brain, we will be led to suppose that every sensation originates in the organ appointed for that sensation. Thus we are conscious that our eyes, not our brain, are the parts of our body which immediately perceive the light; our fingers, or any other parts of the body, feel what is applied to them; and of consequence we have reason to believe that the animal spirits, nervous fluid, or whatever we please to call it, proceed from the surface of the body inwards to the brain, not outwards from the brain to the surface of the body. The brain itself seems to resemble a large collection or reservoir of water, in which the sensations, like so many small streams from every part of the body, unite, and in which our intellectual faculties reside in a manner totally inexplicable by us. Thus far it seemed necessary to theorise, in order to form some idea, however obscured, of the connexion between the nerves and our sensitive and intellectual, or, if we please to call them so, our spiritual faculties.

21. In consequence of this very intimate connexion between the blood and nerves, it is easy to see that any injury done to the one may very greatly affect the other; and that a very slight, nay, to us imperceptible, change in the organization of either, may produce the most grievous, and even incurable disorders throughout the whole body, or in any particular organ. Let us now consider a little farther the blood-vessels.

22. It hath been a question, whether in the structure of these vessels nature hath observed an exact proportion. For instance, if the blood passes by a kind of starts through four cavities, as we are assured that it does, it seems natural to suppose that these four should be exactly equal. This, however, hath been denied; and some, from its accommodating the human frame to their theory, have fancied that they saw the use of such disproportionate work. Dr. Huxham expresses himself in the following words: “Nor doth the air only refrigerate the blood, but, by preventing its too great ebullition, and condensing it, hinders it from bursting the vessels. This indeed is of exceeding great importance, if, with the very learned Helvetius, we suppose the capacity of the right ventricle of the heart to be greater than that of the left, and that the pulmonary arteries are larger than the correspondent veins; for it thence follows, that the blood ought to be considerably condensed by the inspired air, that an equal quantity of blood may be received, in one and the same time, by the pulmonary veins and left ventricle of the heart, that is thrown off from the right ventricle, and through the more capacious pulmonary arteries. This indeed many deny, asserting quite the contrary. It is necessary, however, that the aorta should receive as much blood from the left ventricle of the heart, as is thrown off from the right ventricle through the pulmonary artery; and that in the very same and equal time, or a fatal deluge would soon overwhelm the lungs, because the contraction of each ventricle is made at one and the same time; we always find therefore the aorta and pulmonary artery, in a natural state, equal on this account; also the capacity of the ventricles ought to be equal, that they may receive, in one and the same space of time, equal quantities of blood,” &c.

If any thing farther is necessary upon this subject, we may still observe, that if the blood were at all condensed by the air, it would be so unequally, because the air is at some times much colder than at others; and thus the disproportion of the cavities of the heart to one another could not fail of producing the most disagreeable if not fatal effects. We often see what terrible consequences ensue upon the enlargement of any part of an artery near the heart; and these would, sometimes at least, be felt by every individual.[50]

It is true, indeed, that this objection will in some degree hold, even though we suppose all the cavities of the heart to be equal, and the capacities of the blood vessels to be perfectly uniform throughout the whole body. For, if we suppose the blood to be at all condensed in the lungs by the coldness of the atmosphere, it must undoubtedly follow, that while passing from them it occupies less space than before it arrives at them. Hence the pulmonary vein, the left auricle of the heart, the left ventricle, the aorta, and all the rest of the arteries for a considerable way, must be comparatively empty, even though they receive as much fluid as fills the vena cava, right auricle and ventricle of the heart, and pulmonary artery. The equality which ought to prevail in the system, and which indeed cannot be dispensed with, can only take place in those remoter branches of the arteries in which the blood has reassumed its former state of dilation or rarefaction.

23. If we consider this matter attentively, we shall find it not a little mysterious. Every time we breathe out the air we have sucked into our lungs, a considerable quantity of moist vapour is breathed out along with it; but it has been proved by undeniable experiments that the emission of aqueous vapour from any substance cools it in proportion to the quantity of vapour emitted. Every breath we draw, then, cools the lungs, and consequently the blood, to a certain degree, and, as the number of times that we breathe in a day is exceedingly great, the cold produced by the evaporation ought to be in proportion. But we see that, notwithstanding all this cooling, whether we breathe cold air or hot air, the temperature of the body remains still the same. The air then, though constantly carrying off the heat of the body, does not cool it in the least by its action on the lungs. The only possible way of solving this apparent contradiction is, by supposing that the air, when acting upon the blood in the lungs, leaves precisely as much heat as it carries off, and therefore, though we breathe ever so long, we cannot by this means become either hotter or colder.

24. To illustrate this subject, we might now enter into an inquiry concerning the origin and cause of animal heat; but this will be touched upon hereafter. We shall here only take notice that the heat of the body is almost universally allowed to proceed from the lungs. It has likewise been demonstrated, that the air does in fact contain an incredible quantity of heat, even when it appears to us to be extremely cold. A certain proportion of this heat is separated from it every time we breathe; and if, either by the mixture of other fluids with the air we breathe, or by any change in the organization of the body itself, a greater or smaller proportion of heat should be communicated to the blood, disease must ensue.

25. To sum up then what has been said concerning the blood and nerves: The whole mass of fluid passes from the right side of the heart to the lungs. In the lungs it receives from the air something[52] necessary to the functions of life and sensation, and purifies itself from those matters which might prove pernicious. From the lungs it passes to the left side of the heart, and thence through the whole body. In its passage through the body, it is accompanied with nerves, which, taking up from the arterial blood that vital spirit received from the air, convey it to all the organs of motion, of sensation, and to the brain, where the whole powers of perception being united form our intellectual faculties, and, as far as our senses can perceive, the human spirit itself. The blood, thus deprived of its spirit, is collected from all parts of the body by the veins, and returned to the right side of the heart, from whence it is again sent to the lungs, and the process carried on as before. This hypothesis concerning the peculiar function of the nerves I first inserted in the Encyclopædia Britannica, second edition, under the article Blood, in the year 1778. It has been since continued in the third Scots edition, and from thence into the Irish and American editions.

26. It has already been observed, that the body is subjected to a continual waste. One source of this waste is the breath, by which a considerable part passes off in vapour. A great quantity also passes off by the pores of the skin; frequently in a perceptible liquid called sweat, but oftener in an invisible vapour from all parts of the body, called insensible perspiration. The latter has been thought to be the great source of waste to the human body; and it is certain, that if any person in health be weighed when he rises in the morning, he will be found considerably lighter than when he went to bed. The loss of weight in this case proceeds not only from the pores of the skin, but from the lungs; but though physicians have made a general allowance for both these, I have not heard of any experiment by which we can determine how much passes off by the one, and how much by the other, nor indeed does it appear easy to make such an experiment. Galen plainly overlooks the perspiration from the lungs entirely. “This excrementitious vapour (says he) is expelled through small orifices, which the Greeks call pores, dispersed all over the body, and especially over the skin, partly by sweat, and partly by insensible perspiration, which escapes the sight, and is known to few.” Sanctorius, and the succeeding writers, have classed both together indiscriminately; allowing the discharge to be so great, that if eight pounds of aliment be taken in, five of them pass off in this manner. In a system of anatomy, published at Edinburgh in 1791, the author says, that the discharge by the skin “is even much larger than this (the discharge from the lungs we may suppose) since it not only throws off a quantity of the aliment, but likewise what is added to the blood by inhalation, which, entering often in a very considerable quantity, is thus again expelled.” The same author likewise says, that the “perspirable matter from the skin is principally water,” and that it issues in such quantity as to be seen in subterraneous caverns evidently flying off from the surface of the body like a dense vapour. But other physiologists, particularly Dr. Blumenbach, inform us, that the matter of insensible perspiration is quite similar to the discharge from the lungs, particularly containing a great quantity of fixed air. The same account is given in Chaptal’s chemistry, on the authority of Messrs. Milly and Fouquet. This may be looked upon as a valuable discovery, especially in conjunction with that related by Drs. Beddoes and Girtanner, viz. that the flesh of animals contains a quantity of oxygen. Dr. Girtanner obtained a quantity of this air from the raw flesh of animals, and says that it may be repeatedly obtained by exposing the flesh to the atmosphere, and distilling with a heat of 60 or 70 degrees of Reaumur’s thermometer (something below that of boiling water.) Hence it is natural to conclude, that, as the discharge from the lungs purifies the blood from its useless parts, so does the insensible discharge from the skin purify the solid parts from those particles which are no longer useful. The probability of this also becomes greater by considering, that in diseases, when the quantity of matter to be thrown off is very great, the skin becomes foul, the teeth furred with black sordes, &c. all which disappear as soon as the quantity of the offensive particles is reduced to its natural standard. As to any considerable quantity of aqueous vapour being discharged this way, unless in case of sweat, it does not seem probable; for in such a case our clothes would always be moist; and in the night time the accumulation of moisture would certainly be perceptible. The sweat is entirely of a different nature from the insensible perspiration, and blood and even sand has been known to issue through the skin along with it. (See the Anatomical System above quoted.)

27. This very considerable waste of the body is repaired by the aliment taken into the stomach. In the mouth it is mixed with a considerable quantity of the liquid called saliva, and in the stomach with another called the gastric juice, with which that organ always abounds. From the stomach it passes into the intestines, where it is mixed with other two fluids; one called the pancreatic juice, the other the bile. This last is of a yellow colour, and is sometimes produced in enormous quantities, insomuch that Dr. Wade, in his account of the fevers in Bengal, mentions some patients who have voided by stool half a gallon of bilious matter in one day.

28. In the stomach principally the aliment undergoes a certain change called digestion, by which it becomes capable of being converted into the substance of the body. Much has been inquired and disputed, to no purpose, about the nature of this change, and how it is effected. One party has declared for attrition; a second for putrefaction; a third for heat; a fourth have supposed that our meat was digested by chewing; as if, like the lobster, people had teeth in their stomach! and, lastly, some learned moderns, after much pains and trouble, have found out that it is digested by solution. Dr. Moore has summed up the discoveries concerning digestion in the following words: “The food, being previously divided and blended with the saliva and air by mastication, (chewing) is swallowed, and meets in the stomach with the gastric juice, whose dissolving power, assisted by the natural heat of the place, is the principal agent in digestion. The process is completed by the pancreatic juice and bile, the nutritious parts of the food being by this process converted into chyle for the support of the body, and the grosser parts thrown out.”[53]

29. The inside of the stomach and intestines are full of the mouths of innumerable small vessels, which continually suck up from the aliment, as it passes downwards, the finer parts, in form of a white liquid, called chyle; and from the whiteness of their colour the vessels have the name of lacteals, from the Latin word lac, milk. After passing through the substance of the stomach and intestines, and running along the membrane called the mesentery, to which the intestines are attached, the lacteals unite in a large reservoir called the thoracic duct; and this again opens into a large vein on the left side, called the subclavian, which conveys the blood from half the upper part of the body; soon after terminating in the vena cava, by which the chyle is conveyed to the heart, thence to the lungs, and so on in the common course of circulation. The conversion of the chyle into blood is called the process of sanguification.

30. The blood, thus formed out of the aliment we swallow, is not one uniform fluid like water, but composed of three distinct substances; one, which gives it the red colour, and seems to be composed of little round globules; another, quite colourless, but of a viscid nature, and which very soon coagulates, called the lymph; and a third, of a yellowish colour, and retaining its fluidity much longer, called the serum. A remarkable property of this last fluid is, that air can act through it upon the blood; for Dr. Priestly found that a portion of black blood assumed a bright, florid colour from the air, even though covered with serum an inch deep. When blood is drawn, the red globules are detained by the lymph which coagulates, and both together form the red mass called crassamentum; the serum remaining fluid, and retaining its name.

31. Besides these fluids, the blood either invisibly contains, or is capable of being converted into, a great many others; for all the fluids in the body are separated from it, and all of them, the bile only excepted, from the arterial blood, before it has lost that portion of its spirit which it imbibes from the air. When a fluid is to be secreted, sometimes it is done only by an infinity of small vessels branching off from the arteries, and depositing the liquids which pass through them in particular places; and such are the fluids which moisten the inside of the body, and which are carried off by the breath, or by sweat. But this separation does not by any means hinder the artery from terminating in its usual way in a vein, for in no case is the whole substance of the blood converted into any other liquid; all of them appear to be contained in it. But the greatest number of fluids are separated by means of certain substances called glands. These are small round or oval shaped bodies; each of them enclosed in a membrane or skin which separates it from the other parts, and each furnished with a small tube called the excretory duct, through which the liquor separated in the gland passes to its place of destination. Each gland has also an artery and nerve, and a vein to bring back the blood after it has parted with the fluid intended to be separated. The bile is separated in the liver from the blood of a large vein called the vena portarum, formed by the union of some of the veins of the intestines and mesentery. This vein branches out through the liver like an artery, terminating in other veins, which at last bring back the blood to the heart.

32. As the human body is thus furnished with an apparatus for separating and carrying off, it is also furnished with one for absorbing or taking in. All the inward parts of the body are moist; and the moisture is furnished by the small vessels above described, and which separate part of the lymph from the blood. By such continual separation the cavities of the belly, breast, brain, &c. would soon be filled with liquid, were not some means provided for carrying it off as fast as it is formed. The means in question are a set of small vessels called lymphatics. These “arise from the internal surface of the breast, belly, and every cavity of the body; they also overspread the whole external surface of the body, and large lymphatic vessels are usually found close to the large blood vessels of the extremities, besides those small superficial ones which lie above the muscles in the cellular membrane (the fat or rather the membrane containing it.) The large viscera generally have two sets of lymphatics, one lying on the surface of the viscus, and the other accompanying the blood vessels belonging to it. The faculty of absorption, though refused to the lymphatics, was ascribed by many anatomists to common veins, and this opinion continued to prevail in some degree, until Hunter and Monro totally overturned it, exploding at the same time the notion that any of the lymphatics are continuations of arteries, and establishing, beyond a doubt, that all are absorbent vessels.”[54] All the lymphatics terminate in the thoracic duct; so that the liquid separated by the exhalant arteries (so the vessels are termed by which that fluid is separated) is again mixed with the blood, and again performs the same offices.

We have now taken a review of the several parts of the human body, slight and superficial indeed, but such as the limits of this work would allow, and sufficient to furnish to those entirely unacquainted with medical matters some general ideas on the subject. We have seen that the body, in general, consists principally of four great parts, the blood-vessels, the lymphatic vessels, the nerves, and the muscles. Besides these we enumerate the glands and membranes; the former being nearly allied to the blood-vessels, the latter apparently to the nerves. The bones, having no concern with our present inquiry, are not taken notice of. The stomach and intestines, being principally composed of muscular fibres, nerves, and blood-vessels, must be considered as belonging to these departments. Each of these large divisions has obtained the name of system; and even the subdivision of the blood-vessels into arteries and veins. Thus the arteries of the body, taken collectively, are called the arterial system; the veins the venous system; the brain and nerves the nervous system; the muscles the muscular system; the lymphatics the lymphatic system; and the glands the glandular system; &c. These appellations have been given for the sake of distinctness and perspicuity, but they have had a bad tendency. Insignificant disputes have arisen concerning the superiority of one system to the other, and which is to be accounted the primum mobile of the body. By observing also the general structure of the body in a more full and ample manner than that of the parts which compose it, physicians have been apt to generalize too much in their theories, and to fancy that from a few obvious laws they might be able to explain the phenomena of disease in almost every possible variety. To illustrate this, let us take the blood for an example. This to sight appears an homogeneous fluid; and Boerhaave and others have ascribed diseases to some defect or bad quality of the blood. But this fluid consists of three parts, each, as far as we can perceive, essentially distinct from the other; viz. the lymph, serum, and red globules. As each of these happens to be diseased, the cure must be different; or if two happen to be diseased, the medicines must still be varied. But, besides these general diseases arising from what, like the blood, is common to the whole body, each component part of the body has an arterial system, a venous system, a nervous and lymphatic system, &c. belonging to itself; all of which, though dependent on the body at large, have yet laws of their own, in consequence of which any one of them may be considerably diseased without much affecting the general system; and this constitutes what is called local disease. Again: The parts of the body are so connected with one another, that the disease of one may show itself in another; or it may affect the whole body in such a manner as to produce a general disease; though Dr. Rush considers this last, at least from injuries of the viscera, as a rare occurrence;[55] but we certainly know that general diseases are very often followed by evident diseases of particular organs; and in these cases it is impossible to say whether the general disease did not begin, though imperceptible to us, in that very organ in which we suppose it to terminate when the local disease was come to such an height as to be evident to our senses. In some cases it is plain that local injuries will bring on most violent diseases of the whole system. Thus a local inflammation of the end of one of the fingers, by physicians called a paronychia, has been known to induce a most violent fever, nay, even to occasion death. These violent symptoms end as soon as the suppuration is completed; so that, were it not for the excessive pain of the inflammation, we might be apt to suppose that the fever terminated in the suppuration, whereas it evidently was occasioned by the local disease, or the tendency of the part to suppurate; the pain and inflammation being necessary preliminaries. Again: When an intermittent fever is said to terminate, or to be followed, by a hardness of the liver, we do not certainly know whether an original disease of the liver might not have been the cause of the intermittent. From a consideration of all these things, viz. the extreme diversity of parts which compose the human body, the ultimate invisibility of the structure of each, the incomprehensible manner in which they are united, the equally incomprehensible dependence they have upon one another in some cases, and independence in others, the numerous laws by which they are governed, and which must be very much unknown to us, the invisible and incomprehensible nature of the powers which act upon them, &c. &c. I say, when we consider all these things, the boldest theorist must be humbled when he attempts to account for the phenomena of disease in any one instance. The excessive difficulty in which we are involved is beautifully described by Dr. Ferriar when speaking of hysterics; and obstacles equally insuperable by our theories will undoubtedly be met with in any other distemper. “We are ignorant (says he) by what laws the body possesses a power of representing the most hazardous disorders, without incurring danger; of counterfeiting the greatest derangement in the circulating system, without materially altering its movements; of producing madness, conscious of its extravagances; and of increasing the acuteness of sensation by oppressing the common sensorium. In hysterical affections all these appearances are excited, which are incompatible with the reasonings of every system-maker who has yet endeavoured to explain the inexplicable. Nature, as if in ridicule of the attempts to unmask her, has, in this class of diseases, reconciled contradictions, and realized improbabilities, with a mysterious versatility, which inspires the true philosopher with diffidence, and reduces the systematic to despair.”

Notwithstanding all these difficulties, however, physicians have theorised, and that with such animosity, as if all the arcana of nature had been laid open to every professor who thought proper to invent or new-model a system; though the constant succession of theories might certainly have shown them the vanity of such attempts. Some of these we must now consider.

Medical theorists have exerted their greatest abilities in explaining the nature of those general diseases affecting the whole body, denominated fevers; and which are likewise called acute diseases, from the violence with which they sometimes attack, and the rapidity with which they run through their course. Dr. Fordyce says, that fever will sometimes kill in five minutes from the first sensation of uneasiness. Ancient physicians have described a number of fevers, which they supposed to be of different species, and accordingly have distinguished by different names. Modern system-makers have added to the number; so that a bare detail of the names which they have given to their divisions and subdivisions, would constitute a very formidable catalogue; but the latest practitioners are decidedly of opinion that there is but one kind of fever, varying itself according to circumstances. Dr. Rush declares himself of this opinion in the most express and positive terms. “There is (says he) but one fever. However different the predisposing, remote or exciting causes may be, . . . still, I repeat, there can be but one fever. . . . Thus fire is an unit, whether it be produced by friction, percussion, electricity, fermentation, or by a piece of wood or coal in a state of inflammation.”[56]

“I have said that there is but one fever. Of course I do not admit of its artificial division into genera and species; a disease which so frequently changes its form and place, should never have been designated, like plants and animals, by unchangeable characters. . . . Much mischief has been done by nosological arrangements of diseases. They erect imaginary boundaries between things which are of an homogeneous nature. . . . They gratify indolence in a physician, by fixing his attention upon the name of a disease, and thereby leading him to neglect the varying state of the system, &c.”[57]

So much then having been said and written upon the disease in question, one might be apt to suppose that the nature of fever would have been thoroughly investigated, and its causes explained in the most satisfactory manner, long before this time. Instead of this, however, we find it still like a word which every body uses, and nobody understands. Dr. Fordyce, who has lately written a treatise on the subject, endeavours to prove that there is not any single symptom from the existence of which we can certainly determine the presence of this disease. “Fever (says he) has obtained its name in Greek, Latin, Arabic and Persian, principally from the idea of heat: pur, in Greek fire; febris in Latin, from fervere, to burn,” &c. This idea, he goes on to demonstrate, is erroneous; as the body of a feverish patient frequently sinks the thermometer below the natural standard; while the patient sometimes finds himself cold when the thermometer shows him to be really hot, and hot while the same instrument shows him to be cold. Neither is cold, followed by heat, a certain indication of the presence of fever, as many fevers begin without any previous sensation of cold. Frequency of the pulse also is no certain sign; and having discussed this last symptom he concludes thus. “If we examine the restlessness, anxiety, state of the tongue, head-ach, or any other of the symptoms which often take place in fever, we shall find that they also may be present when there is no fever, and absent in a patient afflicted with this disease; and therefore we cannot allow that there is any pathognomic symptom of fever.”[58] Dr. Rush declines giving any definition of fever;[59] but, with all due deference to these two very experienced physicians, we must account such extreme scepticism altogether erroneous. If fever cannot be defined, it cannot be described; for a definition is no other than a short description. If again there be no single symptom by which the presence of fever can be known, it is impossible that there can be any combination by which it can be known, any more than we can form an unit by any combination of cyphers. In fact Dr. Fordyce himself is at last obliged to acknowledge that there is a certain symptom with which fever generally begins; and, by his insisting upon it in various parts of the work, we must certainly be induced to suppose that it was by this sign principally that he determined whether his patients had a fever or not. “The first appearance (says he) which generally takes place is uneasiness and restlessness; a general uneasiness, the patient feeling himself ill, but incapable of fixing on any particular part of the body. This uneasiness affects the mind at the same time. Perhaps in this case it is the mind that is first affected. . . . Along with this uneasiness there is a restlessness, the patient wishing to change his place or posture frequently; the mind cannot likewise rest upon one object; it often wanders from one to another subject. At the same time there is a feel of weariness which resists the disposition in the patient to change his place and posture, and resists the disposition of the mind to alter the object of its attention, rendering the wish for such changes ineffectual. With these arises an actual inability of exerting the muscular powers, or performing any of the functions of the body; and also an actual inability of exercising the great faculties of the mind, the powers of perception, memory, arrangement of ideas, and of the judgment, in the same degree that they existed in health. The degree in which these take place is extremely different in the attacks of different fevers; but these appearances are very rarely absent, although indeed they may also happen in other diseases.”

Dr. Rush accounts the lassitude with which fever begins, one of the transient phenomena of it; and this with other phenomena he calls symptoms. Such as are more permanent and fixed, and which by other writers have been reckoned different species, he calls states; and of these he enumerates forty. Such as have any relation to the plague are as follow.

I. The MALIGNANT state, known by attacking frequently without a chilly fit, is attended with coma, a depressed, slow or intermitting pulse, and sometimes by a natural temperature or coldness of the skin. . . . This depressed state of fever more frequently when left to itself terminates in petechiæ, buboes, carbuncles, abscesses and mortifications, according as the serum, lymph, or red blood, is effused in the viscera or external parts of the body.

2. The SYNOCHA, or common inflammatory state; attacking suddenly with chills, succeeded by a quick, frequent and tense pulse, great heat, thirst, and pains in the bones, joints, breast or sides.

3. The BILIOUS state of fever; known by a full, quick and tense pulse, or by a quick, full and round pulse without tension, and by a discharge of green, dark coloured or black bile from the stomach and bowels. This state sometimes assumes the form of an hectic; the patient feels no pain in his head, has a tolerable appetite, and is even able to sit up and do business.

4. The TYPHUS state; known by a weak and frequent pulse, a disposition to sleep, a torpor of the alimentary canal, tremors of the hands, a dry tongue, and, in some instances, a diarrhœa. Sometimes it assumes symptoms of synocha on the eleventh, fourteenth, and even twentieth days. The common name of this state is the nervous fever.

5. Intermissions, or the INTERMITTING and REMITTING states, occur most distinctly and universally in those which partake of the bilious diathesis.

6. The SWEATING state occurs not only in the plague, but in the yellow fever, small pox, pleurisy, rheumatism, hectic and intermitting states.

7. The FAINTING state; occurring in the plague, yellow fever, small pox, and some states of pleurisy.

8. The BURNING state. This is attended not only with an intolerable sensation of heat in the bowels, but with a burning sensation excited in those who touch the patient’s skin. It occurs mostly in the remitting fevers of Asia.

9. The CHILLY state differs from a common chilly fit by continuing four or five days, and to such a degree that the patient frequently cannot bear his arms out of bed. The coldness is most obstinate in the hands and feet. A coolness only of the skin attends in some cases, which is frequently mistaken for an absence of fever.

10. The INTESTINAL state; including the cholera morbus, diarrhœa, and cholic.

11, 12, 13, 14, 15. The APOPLECTIC, PHRENETIC, PARALYTIC, LETHARGIC and VERTIGINOUS states.

16. The ERUPTIVE state; including the small pox, measles, and other exanthemata of Dr. Cullen.

17. The HÆMORRHAGIC state; known by fluxes of blood from various parts of the body.

18. The CONVULSIVE or SPASMODIC state. Convulsions are frequently attendant on the malignant state of fever.

19. The CUTANEOUS state; attended with various eruptions on the skin, particularly petechiæ.

These include the most remarkable varieties described by physicians as different species. From the subsequent account of the symptoms of the plague, it will appear that this single distemper monopolises, as it were, the symptoms, at least the most dangerous and terrible, belonging to them all. Those nosologists therefore who suppose the states of fever above described to be different species, instead of saying that the plague belongs to one kind of fever, ought to say that it is a complication of a great many different kinds. But here a question arises: Do all the varieties of fever just now described, or do all the other fevers described by different authors, include all the different modes by which the plague makes its attack? If so, then we know that the plague really partakes of the nature of fever, or may be accounted the highest degree of it. This is the opinion of Dr. Rush; for in his 4th vol. p. 153, he considers the different inflammatory states of fever, according to their strength, in the following order. 1. The plague. 2. The yellow fever. 3. The natural small pox. 4. The malignant sore throat, &c. To this I can have but one objection, and to me it appears insuperable; viz. that the plague frequently destroys without any symptom of fever; and, if so, we must certainly account it a distemper of another kind. To decide this matter, let us compare the symptoms of the most violent fever with what happens in times of violent pestilence. We can scarce imagine a fever more powerful than that which destroys in five minutes, and the following is the description of it from Dr. Fordyce. “When the first attack of fever has been fatal, it has been classed among sudden deaths, and all of these have been very erroneously called apoplexy, or syncopy (fainting.). . . . When the attack is fatal, it sometimes kills in five minutes, sometimes it requires half an hour, seldom longer than that time. While the patient is yet sensible, violent head-ach with a great sense of a chilliness takes place, the extremities become very cold, and perfectly insensible; there is great prostration of strength, so that the patient is incapable of supporting himself in an erect posture; he becomes pale, his skin is of a dirty brown, and he is soon insensible to external objects; the eyes are half-open, and the cornea somewhat contracted. If the patient goes off very soon, the pulse is diminished, and at last lost, without any frequency taking place, but if it be longer before he dies, the pulse becomes excessively small and frequent; all the appearances of life gradually subside, and the patient is carried off. Of this the author has seen instances, sometimes at the first attack, oftener in the returns of the disease, although very few.”

This no doubt is very terrible, and no plague whatever can exceed it. Indeed, when death is the termination, it signifies little what the disease is called. But the question is not whether fever or plague is the most dreadful, but whether they are the same. Now, from the above description, it is plain that fever never kills without some warning. In the present instance, head-ach and chilliness give a certain, though short, warning of the ensuing catastrophe; but, in violent plagues, Dr. Sydenham informs us, that people have been suddenly destroyed as if by lightning. Dr. Guthrie assures us that in the last plague at Moscow he has seen soldiers drop down suddenly as if they had been struck by lightning, or by a musket ball; yet some of these recovered by bleeding and proper management; but it is certainly not unreasonable to suppose that many, who were not thus taken care of, perished. Dr. Hodges speaks of the contagion of the plague in the most energetic terms. He says, “it is so rare, subtile, volatile and fine, that it insinuates into, and resides in, the very pores and interstices of the aerial particles. It is said to be of a poisonous nature also, from its similitude to the nature of a poison, so that they seem to differ in degree only; for the deadly quality of a pestilence vastly exceeds either the arsenical minerals, the most poisonous animals or insects, or the killing vegetables; nay, the pestilence seems to be a composition of all the other poisons together, as well as in its fatal efficacies to excel them. . . . The contagion of the plague is more active than lightning, and in the twinkling of an eye carries to a distance putrefaction, mortification and death. As for the manner whereby it kills, its approaches are generally so secret, that persons seized with it seem to be fallen into an ambuscade or a snare, of which there seems to be no suspicion. . . . In the plague of 1665, as in many others, people frequently died without any symptoms of horror, thirst, or concomitant fever. A woman, who was the only one left alive of a family, and in her own opinion in perfect health, perceived upon her breast the pestilential spots, which she looked upon to be the fatal tokens; and in a very short space died, without feeling any other disorder, or forerunner of death. . . . A youth of a good constitution, after he had found himself suddenly marked with the tokens, believed at first that they were not the genuine marks, because he found himself so well; yet he was dead in less than four hours, as his physician had prognosticated. A fever, however, did for the most part show itself, and was always of the worst kind. Sometimes it seemed to resemble a quoridian, sometimes a tertian; there never was a total cessation, but every exacerbation was worse than before.” In like manner the author of the Journal of the Plague Year informs us that many, supposing themselves, and supposed by others, to be in good health, would suddenly find themselves seized with great sickness, crawl to a bench, and instantly expire. “Many (says Dr. Hodges) in the middle of their employ, with their friends and other engagements, would suddenly fall into profound, and often deadly sleeps.”

It is needless to multiply examples: the above are sufficient to show that the plague, when in its most violent state, kills suddenly and imperceptibly, and that like the bite of a vampire,[60] without producing any sensible disorder. In a state somewhat inferior, it excites the most malignant fevers; in one still inferior it produces fevers of a milder nature, and so on until we find it so mild, that those infected with it are not even confined to their bed. In all this inquiry, however, we find the secrecy and invisibility of the pestilence, so often mentioned in scripture, still confirmed. Other distempers may “waste openly at noon-day,” but this always “walks in darkness.”

In one of the inferior stages of this distemper the body is affected with those eruptions named buboes and carbuncles. Dr. Patrick Russel, in his treatise on the plague at Aleppo, divides the symptoms of the distemper into six classes. In the first there were no eruptions, and all the patients of this class died. In the second, and all the rest, there were buboes and carbuncles. But, in the latter of these especially, it is worthy of remark, that they appear neither as a suppuration, nor as a common mortification, but like the eschar formed by a caustic, which can scarcely be cut by a knife. This appearance is not to be met with in any other disease. In many there are mortifications of various parts of the body, but all these are soft, and seemingly corruptions of the flesh. When a person dies of any ordinary distemper, the flesh soon corrupts and dissolves, but there is no example of its turning to a hard eschar like that made by a hot iron, or the caustic with which issues are made. This shews not merely a cessation of life, but the operation of some very active power in the body, like fire, tending to destroy the texture of it entirely, and to reduce it to a cinder. This power seems also to operate internally in the fleshy parts; for when the bodies of those were opened who died with the tokens, as they are called by Dr. Hodges, upon them, the mortification was always found much larger inwardly than it appeared to be on the outside. The tokens themselves are by Dr. Hodges called “minute distinct biasts, which had their origin from within, and rose up in little pyramidal protuberances, sometimes as small as pins’ heads, at others as large as a silver penny; having the pestilential poison chiefly collected at their bases,” &c.

That the plague was by the ancients reckoned a disease of a nature different from all others, appears from Galen, as quoted by Deusingius. “What is called the pestilence is most properly remarked by Galen not to be a genus of any known disease. For whatever diseases and symptoms are associated with the plague, truly and properly so called, the same are wont to be called pestilential diseases; of which indeed there are an innumerable multitude, and these not always nor every where the same.”[61]

In like manner Diemerbroeck, as quoted by Allen, gives his opinion, that “The plague is something different from a fever, and a fever is only a symptom of it, as I have very often observed; and therefore some very ill define the plague by a fever, since a fever does not essentially belong to it. . . . A pestilential fever, the companion of the plague, is not occasioned by a pestilential venom, but by the mediation of putrefaction; that is, it is not produced because the humours are infected with the pestilent venom, but because the heart, being irritated, overwhelmed and much weakened by the pestilent venom, can neither duly digest and rarefy, nor govern and sufficiently discharge the infected humours; which for this reason putrefy and acquire a preternatural heat, and so excite a fever; which by reason of the foresaid secondary cause, is different and distinct from the plague, and a symptom of it. This is confirmed both by the maxims and authority of the ancients and moderns, as well as by practice, and evident examples.”

Thus it appears, both by fair reasoning by induction from facts, and from the authority of the greatest physicians, that the plague is certainly a disease by itself, and entirely distinct from all others. Hence it follows, that, though we could investigate the causes of fever in their utmost extent, we might still be ignorant of the true plague. That nothing, however, may be omitted, let us now consider what physicians have advanced on this subject, and what progress they have made in ascertaining the sources from whence so many direful calamities are derived.

In an inquiry of this kind, or indeed concerning any cause whatever, it is plain that the nature of the effect must be first understood. Fever then being an effect, we must begin with investigating its nature. But fever itself is only manifest by certain changes in the human body. Before we can investigate the nature of fever, therefore, we must investigate the human body, and that in a manner very different from what we did before. We must now consider the sources of life; in what manner the vital principle acts upon the body, and by what means its motions can be disturbed, or how they may be rectified when once disordered, &c. &c.

The systems of medicine before the time of Boerhaave are now so generally exploded, that it is needless to take any notice of them; and the reputation of Boerhaave himself in this way seems to be almost expiring. His doctrines, nevertheless, merit some attention, because he takes into account a principle overlooked by succeeding theorists, viz. the cohesion of the parts of the body. That he did so is evident, from his having written upon the diseases of a weak and lax fibre, and the diseases of a strong and rigid fibre. In other respects he followed in a great measure the mechanical physicians of the former century. He therefore took but little notice of the nervous system, as being less subject, or indeed to appearance not at all subject, to the known laws of mechanics. The blood was more manageable. The microscopical discoveries of Lewenhoeck furnished an excellent foundation for his system. This celebrated observer had discovered, or fancied he had discovered, that the red part of the blood is composed of globules. Inaccurate indeed these globules must have been, since each of them was composed of six; four touching one another in the middle, with one above, and one below, thus

. The serum was said to be composed of single globules, and by this attenuation it was supposed that the fluid, instead of red, appeared of a yellow colour. Still, however, this was insufficient. Each of the yellow globules was discovered (either by fancied observations or by conjecture, it matters not which) to be composed of six others, which, singly taken, might constitute the lymph or some other fluid; and thus, like the number of the Beast, we might go on by sixes to the end of the chapter, and solve all the phenomena of nature. In justice to the microscopists, however, it must be observed, that some of them have given a much less fanciful account of the structure of the blood than Lewenhoeck. Mr. Hewson found it composed of vesicles, or small bladder-like substances, with a black spot in the middle. These vesicles dissolved in pure water, but kept their original form, which he says was as flat as a shilling, when a small portion of neutral salt was added to the fluid. The solid particles he supposed to be produced by the lymphatic system; the black particles by the spleen.

The supposed observations of Lewenhoeck were of considerable use to Boerhaave in the forming of his system of medicine, though they seem not to have accorded very well with his doctrine of lentor or viscidity in the blood. But, let this be as it will, having laid it down as the foundation of his theory, that the diseases of the body proceeded from too great a laxity of the fibres, or from too great a rigidity of them, and a great many from this lentor, his practice was accordingly directed to such medicines as he imagined would remove these supposed causes of disease. As the lentor of the blood was one of his favourite suppositions, he was therefore perpetually at war with this imaginary enemy, and dealt very much in saponaceous medicines with a view to break it down. But here it is evident that this great man was mistaken, even though we should allow the existence of lentor as much as he pleased. The viscidity, lentor, or any other state of the blood, is an effect of something. It is part of that state into which the body is brought by the disease. The efforts of the physician therefore ought to be against that which produces the lentor; for, unless this be done, the cause of the disease must perpetually counteract the medicines by producing new lentor as fast as they destroy it; and besides, must have greatly the advantage of the physician, by being already in possession of the whole mass of blood, while the medicines can only enter it very gradually, and that by the stomach and lacteals, instead of being instantly mixed with it, and exerting their power immediately upon the fluid itself.

But besides this mistake, which is common to other systems, Boerhaave’s lentor has been denied, and that upon such strong grounds that it is now universally exploded. Another system quickly succeeded, in which every thing was managed by the nerves. This was introduced by Hoffman, adopted, and perhaps improved, by Dr. Cullen, under whose auspices it acquired such a degree of celebrity, that for a long time it was dangerous to write or speak against it; and the person who had the audacity to do so underwent a kind of medical proscription from the Edinburgh College and all its students. According to this celebrated theorist, the brain is that part of the body first formed in the embryo; it may be seen with nerves proceeding; from it long before the heart or any blood-vessel belonging to it is visible. Hence we are to conclude that this part is necessary to the existence of every other part of the body, though it doth not appear that they are essentially necessary to its existence. The superiority of the nerves to all other parts being thus established, the Doctor undertook to prove that all other parts of the body were formed from them; that the body is nourished immediately from them, and in short that the whole body is in such subjection to the nervous system, that, except for the mere purpose of distending the vessels, we can scarcely know for what end the blood exists; since the nerves can alter its consistence, or that of any of the fluids secreted from it, by a mere affection of that system, without any thing either added to or taken from the vital fluid.

Thus we were compelled to believe that all diseases at their first origin are affections of the nervous system, from whence they are propagated through the whole body. The Cullenian practice in acute diseases, of which the plague is the most violent, was built upon a maxim of Hoffman: “Atonia gigoit spasmos:” Atony produces spasms. In explaining the nature of typhus fever, therefore, with which he classes the plague, the Doctor supposed that the contagion acted first upon the nervous system, by producing therein a debility. The immediate effect of this debility is a spasm, or preternatural contraction of the capillary vessels, or extremely small arteries. Hence the blood finds some difficulty in circulating, and the patient is seized with shivering, and has a sense of cold. When this has continued for some time the system begins to re-act against its enemy; the spasm is resolved, and, the reaction of the system continuing, the action of the heart and arteries is augmented, and the body becomes warmer.

Thus the coldness, shivering, and consequent heat, which constitute the first attack of fever, are very plausibly explained; but in the mode of cure this learned physician fell into the same mistake with Dr. Boerhaave; for though spasm is undoubtedly, even according to himself, an effect, he directs his medicines entirely against it, as if it were a cause. Thus, forgetting what he had just before advanced, that the spasm is occasioned by debility, he recommended the most debilitating medicines and regimen to cure people already too much debilitated; and to such practice his enemies alledged that many fell victims. The theory and practice, however, still kept its ground; and as great numbers of students were every year bred up in the belief of it at Edinburgh College, who carried the principles of their teacher to all parts of the world, it bade fair for becoming universal. But, in the midst of this eclat, the whole system received such a rude shock from the doctrines of John Brown, though at that time not even M. D. as it hath not yet recovered.

Though the author of the new system contended, as much as Dr. Cullen, for the supremacy of the nerves, he did not upon that foundation attempt to establish his practice. He considered the living body as one machine, the whole of which might be acted upon, and always was acted upon by certain powers. It possesses a certain inexplicable property called excitability, capable of being augmented or diminished. Every power which augments the excitability he called a stimulus; the opposite would have been a sedative; but according to this system there is not any sedative, nor can there be one in nature. The reason is, that excitability itself has no existence but in consequence of the action of certain powers called stimulants. The total subduction of these reduces the excitability to nothing; of consequence no power can act against it in a state of non-existence. What other physicians call sedatives, therefore, according to the new system, are only weak stimulants. The fallacy of such reasoning is obvious; but as it does not affect the practice, we shall not spend any time in considering it further.

On the principles just now laid down, the Brunonian system divides all diseases to which the human body is liable into two great classes; the one produced by too much excitement, the other by too little. The former contains those diseases by other physicians called inflammatory; the latter such as are called nervous, putrid, or all in which the powers of life are too weak, and require to be supported. This last is supposed to be much more numerous than the former; and in the cure of these it was that the founder of the system appeared to greatest advantage. A most violent altercation took place between Dr. Brown and the Edinburgh College; yet, notwithstanding all the influence of the professors, and their unanimous opposition to the new doctrines, they found themselves ultimately unable to resist a single man unsupported either by wealth or reputation. The plausibility of his system, and its being obvious to every capacity, overcame every obstacle; so that even the practice of the Cullenians themselves underwent considerable alterations. It is not, however, to be denied that the system hath been considerably improved, or at least altered, by some of Dr. Brown’s pupils, who have had the advantage of extensive practice, and of visiting many different countries; which the Doctor himself never had. His materia medica was besides exceedingly confined; the only medicines he had any great opinion of, being laudanum and ardent spirits. The Peruvian bark he held in very little estimation, as being a weak stimulus. He seems to have been unacquainted with the virtues of mercury, except in the venereal disease, and most probably would have given laudanum in those cases of fever where mercury is found by others to be so efficacious. But this deficiency hath been abundantly supplied by some of his followers. In a work entitled “The Science of Life,” published by Dr. Yates and Mr. McLean, practitioners in the East Indies, we find mercury exhibited in prodigious doses. As a specimen we shall select their third case, which was a dysentery. On the first of September the patient took two grains of calomel and as much opium every two hours. This was continued for two days. On the third, the dose was given every hour; besides which, he had half an ounce of mercurial ointment with a drachm of calomel rubbed into his body. Next day the pills were continued, and the quantity of ointment tripled by thrice rubbing in. This was continued for three days, at which time, an eruption on the skin appearing, it was feared he could not be salivated; this eruption being a sign that no salivation could be produced. The same mode of treatment, however, was persisted in. September 7th the calomel in the pills was augmented to four grains; the warm bath was used, and the ointment continued; but at night twenty grains of calomel and six of opium were given every two hours. At the same time two ounces of ointment, with four of calomel, were ordered to be rubbed in. Next day, though his pulse was almost imperceptible, and his extremities cold, “the medicines were continued as far as circumstances would admit;” with what view it is not said, nor indeed is it easy to be discovered. At one in the morning, however, the patient died; an event not at all surprising. Our authors excuse themselves for this failure by saying that the viscera of the patient were diseased, as was evinced by the impossibility of exciting a salivation; and “that when a patient is evidently incurable by the common practice, it becomes the duty of the practitioner to depart from it.”

No doubt we may readily assent to both these assertions; but though a patient be evidently incurable by the common practice, or by any other, there is no necessity for killing him, or for persevering in a course of violent medicines that evidently make him worse. The whole of this case indeed strongly militates against the doctrine of excitement; for if mercury be such a powerful stimulus to the powers of life in general, how comes it to pass that in the present case the unhappy patient, instead of being in the smallest degree excited, was prodigiously debilitated, and that from the very first time of taking the medicines. This will appear from the following table, exhibiting the symptoms of the disease as they kept pace with the medicines taken.

Days of the Month.	Medicines taken.	Symptoms.
August 29 & preceding.	Ordinary doses of mercury and opium.	Pain of bowels, and frequent stools, growing worse.
Sept. 1 & 2.	Opium and mercury, two grains each, every two hours; besides opiate draughts.	Still increasing.
3d	The opium and mercury as before, but now given every hour; half an ounce of mercurial ointment, with 60 grains calomel.	Stools very frequent, with violent pain in the bowels; extreme thirst, tongue furred, and no sleep.
4th	Pills as usual. Ointmt. thrice rubbed in, once with 120 grains of mercury.	Vomiting during the night. Tongue brown and furred.
5th	Medicines as before.	Violent pain in bowels.
6th	Medicines as before.	Extreme pain on pressing the arch of the colon; frequent stools, profuse sweats, great dejection of spirits.
7th	Pills as before, with four grains of calomel. Mercury in the ointment increased to half an ounce. Warm bath. At night an ounce of mercurial ointment, with two ounces calomel.	As yesterday. An eruption on the skin. At night incessant stools, with violent pain in the belly; profuse sweat.
8th	Pills, ointment & calomel as before. Warm bath thrice. At night two ounces ointment, with four of calomel.	Incessant stools with violent pain; at night with blood. Extreme debility.
9th	Medicines of the same kind, as many as could be taken.	Stools innumerable; extremities cold, pulse scarce to be felt.
10th		Death at one in the morning.

From a consideration of this patient’s symptoms, in comparison with the quantity of mercury taken, it most evidently appears, that it acted in no other way than as an irritating poison; affecting, with extreme violence, the already diseased intestines, and, instead of exciting the vital powers of the whole system, manifestly destroying them. Let it not be imagined, however, that this case is selected from the rest merely because it was fatal, or because it affords an opportunity of finding fault with the practice recommended in the book. It is the only one in which the mercury had a fair trial; and even here it was not very fair, as being conjoined with a great quantity of opium. In the other cases, which terminated favourably, the mercury was overpowered by such horrible doses of opium, that we cannot tell which medicine had the greatest share in the cure; besides, that in other cases the patients were allowed the free use of wine, which we all know to be a powerful stimulant and cordial; but it is not said that the poor man, whose case is above related, had a single drop of wine, or any thing else, except opium, to support him against the action of such a violent medicine.

On this case it is of importance still to remark, that it affords, in the strongest manner, an argument against what our authors say, p. 86, that “mercury acts by supporting the excitement of the whole body, it invigorates each particular part; and thus occasions, to a certain extent, the regeneration of those organs which may have been injured by disease.” In the instance adduced, there is no evidence of a stimulus upon any other part of the system than the bowels, which were already debilitated or diseased in such a manner that they could not bear it. The system in general, instead of being excited, was sunk and debilitated from the very first moment, until at last the excitement terminated entirely by the patient’s death. But further: There is very little probability that mercury or any other medicine whatever can prove a general stimulus, and that for the following reasons.

1. No medicine can assimilate with the substance of the body. Medicines properly so called are here alluded to. Food or drink of any kind taken for the support of the body while in health, however they may act medicinally upon occasions, are excepted.

2. The body is composed of many various substances, each differing in its nature from the other. The nature of the medicine, whatever it may be, is uniform, and cannot act upon substances of different kinds in an uniform manner; and without this there can neither be an universal stimulant, nor an universal debilitant.

3. All medicines, being incapable of assimilation with the body, must be considered, when taken into it, as foreign matter; and the introduction of them at any rate is in fact the creating of a disease. This is evident from multitudes of instances where people by quacking with themselves, and taking medicines unnecessarily, have destroyed their health.

4. As every medicine has one peculiar nature, and one mode of action in consequence of that nature, it must, when introduced into the body, where there are fluids of various natures, act upon one of them more than the rest; and this may be called the chemical action of that medicine upon the body.

5. In consequence of the chemical action of the medicine, the mode by which it is expelled out of the body will be different; for, as all medicines are extraneous substances, they must be sent out of the body as fast as possible; and it is their action upon one particular part which promotes their expulsion. Thus, if from the nature of the medicine it acts in a certain way upon the stomach and bowels, it will vomit or purge, or perhaps both; and by this action it is expelled from the body, along with whatever other matters happen to be in the stomach or intestines; and thus medicines do good only accidentally; for mere vomiting or purging are most certainly diseases; but where noxious matters exist in the bowels, and do not naturally excite these operations, an emetic or purgative is unquestionably useful. Here the authors of the Science of Life reason differently; and it is worth while to refute their argument, as being the foundation of such tremendous practice as nobody of common sense would choose to be the subject of. Of tartar emetic they speak in the following terms. “That tartar emetic is a stimulant of very high power, is evident from the small quantity of it which produces the state of indirect debility that occasions vomiting. It should be given in such a manner as to increase and to support the excitement. But this will be found difficult, as the duration of its action seems to be even shorter than that of opium. If its action does not continue more than a quarter of an hour, might it not be repeated at such short intervals, and the doses so reduced as to allow the establishment of the indirect debility?” This is arguing in a circle. They first suppose that vomiting is occasioned by indirect debility, that is, the weakness produced by an excessive stimulus to the whole system, as in cases of drunkenness; and then, from the existence of vomiting, they prove that a general stimulus had pre-existed. The cases, however, are widely different. In cases of drunkenness, the person feels himself at first exhilarated, alert and active, which shows the existence of a general stimulus. But who has ever found himself exhilarated by taking a dose of tartar emetic? Yet in a general excitement it is absolutely necessary that this exhilaration should take place, because it is an inseparable consequence of an addition of vital power, let it come in what way it will. Thus we know that if a person happens to be much exhausted by fatigue and abstinence, he will be exhilarated and his strength augmented by a single mouthful of meat, as well as by a glass of wine. This shows that both these are general stimulants to the system; but what medicine have we that will produce similar effects? Perhaps opium comes the nearest in the whole materia medica; but the uneasiness it occasions in the stomach manifests a greater action upon it than the other parts; for if the whole body were equally excited, the withdrawing of the stimulus, or its naturally losing its force, could only have the same effect with fasting or fatigue; but the debility of the stomach, the confusion of the head, and other effects which attend a dose of opium, demonstrate that it acts partially, and not equally over the whole body. The Science of Life indeed says that these effects are owing to the improper omission of the medicine, or not repeating the doses in due time. This may be; but no improper exhibition of food, or want of due repetition, will produce such symptoms; which undoubtedly is a proof that food stimulates the system in one way, and opium in another.

6. If any medicine could be found that acted as an universal stimulus or exciter of the whole system, it could not like others be expelled, by any particular evacuation; but, by destroying the balance between the force of the acting powers and the subject on which they act, would most certainly kill, unless very powerful means were used to counteract its effect. The only stimulant we are acquainted with which acts equally on the whole system, and which can be readily exhibited as a medicine, is that pure kind of air called by Dr. Priestley dephlogisticated, by Scheele empyrean, and by the French chemists and their followers oxygen. The exciting powers of this air, when breathed instead of the ordinary atmosphere, are astonishing. It not only augments the appetite, but the power of the muscles, and the inclination to use them; so that without any intoxication or delirium the person cannot refrain from action; and it not only exhilarates the spirits in an extraordinary manner, but beautifies the face. Did the cure of diseases therefore, or any set of them, depend on mere excitation, no other medicine but oxygen would be necessary. What effects it may have in diseases of debility is not yet ascertained; but to persons in health it certainly proves fatal: their bodies are unable to bear its powerful action, and of consequence they waste, and would die of consumptions, if its effects were not counteracted. Nor is this at all an easy matter; for Dr. Beddoes informs us that, by breathing this air for a short time each day, only for three weeks, he found himself in great danger of a consumption, and was obliged to use much butter and fat meat in his diet, besides giving up the use of the air altogether, in order to get clear of its mischievous effects.

Another mode of stimulating or exciting the whole system is, by putting into it a larger quantity of blood than it naturally contains. This is entirely similar to the breathing of oxygen; especially if arterial blood be used, which has already imbibed its spiritous part from the atmosphere. In the last century the transfusion of blood was proposed not only as a mode of curing diseases, but of restoring old people to youth; and Dr. McKenzie, in his Treatise on Health, quotes from the memoirs of the Academy of Sciences several instances of the blood of brute animals being infused into human veins, without any inconvenience. It seems, however, not only a bold but an unnatural attempt to use the blood of beasts for such a purpose; and, however lavish mankind may be of their blood upon certain occasions, it is to be feared that there are few who would be willing to spare any to relieve another from sickness; but indeed little can be said about the practice; as, on account of some bad consequences, or failures, it was forbidden by the king of France, and by the pope’s mandate in Italy, and has now fallen into disuse. In a paragraph at the end of Heister’s surgery (4to edition) it is asserted that the transfusion of blood was productive of madness. Dr. Darwin, however, in his Zoonomia, still proposes the transfusion of blood as a remedy, and even describes a convenient apparatus for performing the operation. In one part of his work he says, “Might not the transfusion of blood, suppose of four ounces daily, from a strong man, or other healthful animal, as a sheep or an ass, be used in the early state of nervous or putrid fevers?” In another place he mentions his having proposed it to a gentleman whose throat was entirely closed up by an incurable swelling, so that he could swallow nothing. This is a disease not very rare, and which always must be fatal; because the patients, though not affected by any sickness, die of hunger; and, to relieve them from this miserable situation, extraordinary attempts are not only allowable but laudable. The Doctor proposed to his patient, “to supply him daily with a few ounces of blood taken from an ass, or from the human animal, who is still more patient and tractable, in the following manner: To fix a silver pipe, about an inch long, to each extremity of a chicken’s gut, the part between the two silver ends to be measured by filling it with warm water; to put one end into the person hired for that purpose, so as to receive the blood returning from the extremity; and when the gut was quite full, and the blood running through the other silver end, to introduce that end into the vein of the patient, upwards towards the heart, so as to admit no air along with the blood. And, lastly, to support the gut and silver ends on a water plate filled with water of 98 degrees of heat; and, to measure how many ounces of blood were taken away, to compress the gut from the receiving pipe to the delivering pipe.” The gentleman desired a day to consider of this proposal, and then another; after which he totally refused it, saying that he was now too old to have much enjoyment of life, and that, being so far advanced in a journey which he must certainly accomplish sooner or later, he thought it better to proceed than return. The Doctor informs us that he died a few days afterwards, seemingly very easy, and careless about the matter. One experiment of this kind I have been witness to; not indeed on a human creature, but on a calf. This creature received into one of its jugular veins a considerable quantity of blood from the carotid artery of another, nearly of the same age (about a month, or little more.) It was impossible to say any thing about how much was transfused; only the bleeding was continued till the animal which lost the blood began to shew signs of faintness. The artery was then tied up, and the orifice in the jugular vein closed. The calf which had lost the blood appeared very languid and faint, but lived a few days in a drooping state; when it either died of itself, or was killed, as being supposed past recovery. The other, which had received the blood, appeared to be in every respect highly excited. It became playful, even in the room where the operation was performed, its eyes assumed a bright and shining appearance, and its appetite was greatly increased. Thus it continued for about a fortnight; appearing all the time to be in high health, and eating much more than usual; but at last died suddenly in the night. From these effects on healthy subjects, however, we cannot infer what would happen in such as are diseased; but it is plain that if the cure of diseases were to depend upon mere excitation, the means are in our power, without any local irritation, which always must take place in some degree by the use of ordinary medicines. This path is not absolutely untrodden: the pneumatic practitioners of the present day have tried oxygen in consumptions, and found it pernicious; and Dr. McKenzie informs us that the transfusion of blood was tried ineffectually in the same.

7. As all the medicines usually prescribed at present are only to be accounted partially stimulant, or as acting upon particular parts of the system, we see that some may promote one evacuation, and some another; while all produce some change in the organization, which may prove useful or detrimental, may increase the disease or cure it, or may produce another, according to the judicious or injudicious application. But for a knowledge of all this we must be indebted to experience: there is not a theory on earth that can lead us a single step.

Before we dismiss the consideration of medical theories, however, it will still be necessary to give some account of the new system as it hath branched out in various ways: for though the fundamental principle is now received by a great number of physicians, yet the superstructure is exceedingly different from what Dr. Brown himself erected and, indeed, from the very same principles we find conclusions made as directly opposite to one another as can be expressed in words. Drs. Yates and McLean, for instance, at Calcutta in the East Indies, have concluded that the plague “is a disease of a very high degree of exhaustion;” which Dr. Brown would have called debility. Dr. Rush at Philadelphia, proceeding also upon the Brunonian principles, determines it to be the most inflammatory of all diseases,[62] and which Dr. Brown would have called a disease of excitement. These two doctrines are, in every sense of the word, as distant from one another as east from west. Let us then consider both, if any consideration can avail us on the subject.

By the ancients it was supposed that diseases were occasioned by something either bred in the body or received into it, and that the power of nature produced, during the course of the disease, a certain change in this matter, called coction, or concoction; which, if we please, we may express by the English word cooking. The matter of the disease, called also morbific matter, thus cooked, was in a state proper for expulsion, and was therefore thrown out by sweat, vomit, stool, &c. or it might be expelled artificially, which could not have been attempted with safety before. Modern systems deny the existence of morbific matter, and resolve all into an affection of the nerves, according to Dr. Cullen by certain sedative causes, but according to Dr. Brown by an accumulation in some cases, and an exhaustion in others, of the excitability or excitement of the body. The Science of Life commences with stating what they suppose to be an improvement of the Brunonian principles, and from which the following account of the origin of diseases is extracted. “Upon the different states of excitability depend all the phenomena of health and disease. There are three states of the excitability. 1. The state of accumulation; when a portion of the usual stimuli is withheld. . . . When a portion of the usual stimuli is withheld, the excitability accumulates, and the body becomes susceptible of impression in the direct ratio of the subduction. This state constitutes diseases of accumulation, or of direct debility. 2. The middle state; when the excitability is such that the application of the accustomed degree of exciting powers produces tone or health. 3. The state of exhaustion. When the application of stimuli has been greater than that which produces healthy action, the excitability is exhausted, and the body becomes less susceptible of impression in the direct ratio of the excess. This state constitutes diseases of exhaustion, or of indirect debility. The states of accumulation and exhaustion of the excitability, in their different degrees, constitute all the diseases to which living bodies are subject.”

Here the chime runs on the word excitability, which is not defined. If we call this property life, then we are only informed, that, as life is more or less vigorous, the body enjoys a greater or smaller degree of health; which we know without any medical instructor. If, instead of the accumulation and exhaustion of excitability, we take the original doctrine of excitement and debility laid down by Dr. Brown himself, we are nothing better. The whole theory is lost for want of the definition of a single word. As long as excitability remains an unknown property, we can explain nothing by it. We may indeed vary our terms. We may call it nervous influence with Dr. Cullen, or sensorial power with Dr. Darwin; but we shall still be as much in the dark as ever; and all that can be made out of our theories, when our language is decyphered, must be, that sometimes people are well, and sometimes they are sick!

Dr. Rush, in his Treatise on the Proximate Cause of Fever, adopts in part Dr. Brown’s system pretty nearly as the author himself laid it down. “Fevers of all kinds (says he) are preceded by general debility. This debility is of two kinds, viz. direct and indirect. The former depends upon an abstraction of usual and natural stimuli; the latter upon an increase of natural, or upon the action of preternatural, stimuli upon the body. . . . Debility is always succeeded by increased excitability, or a greater aptitude to be acted upon by stimuli. . . . The diminution or abstraction of one stimulus is always followed by the increased action of others.” Here it is evident we are as much in want of definitions as ever. We know neither what excitability is, nor what debility is, and yet they are both held out as the causes, and proximate or immediate causes, too, of symptoms produced by things quite obvious to our senses. Thus cold and heat, with which we are daily conversant, are only called the predisposing causes of fever; while debility and excitement, words to which we have no meaning, are said to be the proximate cause. It would certainly be better to throw away such words altogether, and say that cold, heat, &c. cause fevers, without troubling ourselves farther about the matter.

It remains now to take into consideration the pneumatic theories, founded upon the discoveries made by Dr. Black, Dr. Priestley, Lavoisier, and others, concerning various kinds of aerial fluids, or gases,[63] as they are also called. Some of these, particularly that afterwards called fixed air, were discovered by Van Helmont. Considerable advances were made by a German chemist, named Mayow, in the last century; but his book had fallen into such oblivion that his name was scarce ever mentioned, until his discoveries were repeated, and still greater advances made by others. Dr. Hales obtained air from a great many different substances, but was unable to ascertain any thing concerning its nature. Dr. Black of Edinburgh laid the foundation of pneumatic chemistry, by discovering that a certain species of air is capable of being absorbed by earths of different kinds, and that many very heavy substances owe at least one half of their weight to this condensed air. The discovery was accidental. Wishing to obtain a very pure and white lime, he had recourse to the fine white earth called magnesia alba. Some of this he distilled with a heat sufficient to make the vessel red hot. Only a very small quantity of water came over, but the magnesia had lost almost two thirds of its weight. This immense loss was found to arise from an emission of air during the operation; and by other experiments it was likewise found that the air might be transferred from one portion of magnesia to another from which it had been previously expelled; that the existence of this species of air in certain bodies was the cause of that fermentation which takes place when any acid is poured upon them, as vinegar upon chalk or potash. Hence if any of these substances be deprived of its air, it will not any longer ferment in this manner. It must not be forgot, however, that when air thus unites itself with any terrestrial substance it no longer has its former properties. It is reduced exceedingly in bulk, and in proportion to this reduction only the body is increased in weight; and therefore though we say that the air is absorbed, we must still remember that only one part of it is so, and that by far the least considerable in bulk. A violent fire will always expel the air again, and restore it to its former bulk; and again the condensation or absorption of the air is always attended with the production of heat. This last property was not much attended to by Dr. Black, but others have observed it; and the late Dr. Charles Webster of Edinburgh published a theory in which he maintained that condensation was in all cases the cause of of heat. But, however true it may be that condensation of any kind is followed or accompanied by heat, it is evidently necessary to know the cause of the condensation also, otherwise we make no advance in solid theory.

The aerial fluid, discovered by Dr. Black, was one of those most commonly met with. He called it fixed air, from its property of adhering or fixing itself to different bodies. It was found to be the same with that which had been discovered by Van Helmont, and by him named gas sylvestre (spirit of wood)[64] or the fume of charcoal; it was found to be the same with the steam of fermenting liquor, and with that very frequent and dangerous vapour, met with in coal mines, called in Scotland the choke-damp. Like other discoveries, this was quickly pushed beyond its proper bounds, and applied to the solution of phenomena which it could not solve. Dr. MBride, particularly, supposed it to be the bond of union between the particles of matter, or in other words the principle of cohesion itself. It was also supposed to be the substance of those scorching winds, called samiel, met with in Asia and Africa, and which sometimes prove fatal to travellers. The pernicious vapours called mofetes, which sometimes issue from the old lavas of Vesuvius in Italy, were likewise supposed to be the same;[65] but of this, particularly with regard to the samiel, there seems to be no sufficient evidence.

The industry of other experimenters did not long leave theorists without abundance of materials upon which they might exercise their talents. It is impossible in this place to assign to each his proper rank in the way of discovery, or indeed to mention their names. Dr. Priestley has distinguished himself far above the rest. He not only repeated and improved Dr. Black’s experiments on fixed air, but likewise found out a number of other kinds; particularly that from animal substances in a state of putrefaction, which is so pernicious to living creatures, insects excepted; for these last will thrive amazingly in air that would prove certain death to a man. He also discovered that this kind of air, and some others, were absorbed by vegetables, and thence inferred the use of vegetables in purifying the atmosphere. He even analysed the atmosphere itself, and found that it consisted of two different kinds of fluids, one of which he called dephlogisticated, the other phlogisticated air. The former was found to support animal life for a time, the latter to destroy it instantly. Their effects upon fire were the same; the former exciting the most vehement heat and bright flame, the latter extinguishing a fire at once.

The fame of Dr. Priestley’s discoveries quickly reached the continent of Europe; the French chemists repeated his experiments with improvements, as they thought; and indeed certainly made many curious discoveries. Lavoisier was particularly remarkable for his numerous and accurate experiments; but, by his changing entirely the language of former chemists, and substituting a set of new terms of his own invention, he certainly entailed the greatest curse upon the science it ever met with. It belongs not to this treatise to give an account of his system farther than to say, that, from the immense proportion of condensed aerial matter found in most terrestrial substances, he and his followers were led to conclude, that different species of air constitute almost the whole of the terraqueous globe. Water particularly they have absolutely and most positively determined to be a composition of two airs condensed, viz. the dephlogisticated and inflammable, which they call oxygen and hydrogen. However, this doctrine is still opposed by Dr. Priestley and some others.

In the midst of so much theory, and so many new and surprising discoveries, it would have been wonderful indeed if the science of medicine had kept free from innovation. It did not: the new chemistry, with all its formidable apparatus of hard words, was introduced, and thus the study of the science, already very difficult, was rendered still more so. In passing this censure upon the modern nomenclature, as it is called, I am sensible that I must rank with the minority; nevertheless, I have the satisfaction of finding that I am not altogether singular. Dr. Ferriar, in the preface to his second volume, complains, “that, with every attempt towards the formation of a system, new applications of words are introduced, which, though desirable in the art of poetry, are very inconvenient in pathological books, especially when this is done to give an air of novelty to old theories and observations. For, between the ancient language, which practitioners cannot entirely reject, and the new dialect, which they cannot wholly adopt, the style of medical books is reduced to a kind of jargon, that the author himself may possibly understand, but which his readers find it very difficult to unriddle. Hence results a neglect of medical literature, and hence the pernicious habit of regarding as new whatever has not appeared in the publications of the last half century.” To the same or a similar purpose, in the preface to his first volume, he cites Quintilian.[66] “Some have such a multitude of vain words, that, while they are afraid of speaking like other people, by a kind of affected elegance, they confound every thing they have to say with their immense loquacity.”

The pneumatic system naturally arose from a consideration of the composition of the atmosphere we breathe. Finding this fluid to be composed of two others, the one of which would preserve life for some time at least, and the other instantly destroy it, it became natural to think that diseases might be produced by any considerable variation in the proportion of these ingredients. An instrument was soon invented by which any considerable variation in this respect might be discovered; but upon trial this was found to be of very little use. Dr. Priestley himself tried, by means of this instrument, some very offensive air which had been brought from a manufactory, and could find no remarkable difference between it and that which was accounted pure. Still, however, it was evident that by increasing very much the proportion of one of the ingredients, some considerable alteration might be produced, which could not but be perceptible in the human body; and this led to the application of aerial chemistry to disorders of the lungs. The mixture chosen for this purpose was pure dephlogisticated (oxygen) with inflammable air (hydrogen;) and, though this has not been known to effect a radical cure, it certainly has given relief in many cases. In fevers also the application of fixed air (carbonic acid) hath been found advantageous; but with regard to oxygen and some others we have not yet a decided instance of their good effects in any case. Dr. Beddoes indeed is of opinion that it would be of service in the sea-scurvy; but in this (whether his conjecture be right or wrong) the theory is certainly erroneous, as shall presently be evinced.

In considering the pneumatic system it is evident that modern chemists have fallen into the same error with their predecessors, viz. of supposing that every thing which by the force of fire or otherwise they could produce, from any substance, previously existed in it. Hence, as from a piece of bone for instance, a chemist can produce water, salt, oil and earth, it was supposed that these four were the principles or elements of the bone. But this was false reasoning; for if these were really the chemical principles, they ought to have been able to produce some kind of bony substance by mixing them together after they had been distilled. But no such thing could be done; and though we should add to the mixture the whole quantity of air emitted during the distillation, and which escaped the notice of ancient chemists, our success would be no better. In like manner, because in certain circumstances oxygen is obtained from the flesh of animals, it has been concluded that it necessarily exists as an ingredient in their bodies while living; and that, if this kind of air happens to predominate, the animal will be affected in one way, or if hydrogen prevail, in another. But though we have already quoted Dr. Girtanner with approbation as having obtained oxygen gas from fresh meat, yet this does not by any means prove to us that it exists in flesh as one of its component parts. Even in the Doctor’s experiment it was necessary to expose the flesh to the atmosphere in order to procure the gas by distillation; which undoubtedly must excite a strong suspicion that the air in question comes from the atmosphere itself; and, if this is the case, it is not reasonable to suppose that a disease could be cured by any addition of oxygen to the solid parts; because, though sound flesh may have an inclination to absorb this kind of air, we do not know whether it would have such a property of absorption in a diseased state. Indeed in the scurvy, which Dr. Beddoes chooses as an example, experiment seems to determine in favour of fixed air rather than any other. But let us hear Dr. Girtanner himself, who has at large discussed this subject in two memoirs; one upon the laws of irritability, and another on the principle of irritatibility.

In these memoirs we find the Brunonian doctrine set forth with such silence in regard to Dr. Brown himself, that some have not scrupled to charge Dr. Girtanner with literary theft; but this is a matter which belongs not to us to consider: the theory may be very good, whether stolen or not. He changes the word excitability, used by Dr. Brown, for irritability; but hath the misfortune of not being able to tell us what he means by it. He goes on, however, to distinguish the three states of tone or health, accumulation, and exhaustion, as other Brunonians do. Health, he says, in a fibre “consists in a certain quantity of the irritable principle necessary for its preservation. To maintain this state, the action of the stimulus must be strong enough to carry off from the fibre the surplus of this irritable principle which the lungs and the circulation of the fluids are continually supplying. For this a certain equilibrium is necessary between the stimuli applied and the irritability of the fibre, in fine that the sum of all the stimuli acting upon it may be always nearly equal; powerful enough to carry off from the fibre the excess of its irritability, and not so strong as to carry off more than this excess. . . . When the sum of the stimuli acting upon the fibre is not great enough to carry off all its excess of irritability, the irritable principle accumulates in the fibre, and then it is found in that state which I call the state of accumulation; the irritable principle accumulates in the fibre, its irritability is augmented, and the stimuli produce much stronger contractions than when the fibre only retains its tone. . . . When the sum of the stimuli acting upon the fibre is too great, the fibre is deprived not only of the excess of its irritability, but also of some portion of the irritable principle necessary for the tone of the fibre; or, more properly speaking, the fibre loses more irritability than it receives, and, of course, in a short time finds itself in a state of exhaustion; and this exhaustion will be either temporary, or irreparable.”

Here it is evident that we have nothing but Dr. Brown’s system, without the least explanation to render it more intelligible. A definition is still wanting. This invisible and incomprehensible property of irritability ruins our whole fabric; nor can the deficiency be supplied by human art or skill: of consequence we must abandon this part of the system entirely, and come to something more cognizable by our senses. It is impossible, however, to pass over in silence the amazing inattention of the author, in imagining that on such unintelligible principles he could explain other phenomena. “In the state of temporary exhaustion (says he) the fibre loses its tone, and fails for want of irritability. The application of a stimulus while it is in this state will not make it contract. Provided the stimulus be not very strong, it will produce no effect at all, but in a short time the irritable principle will accumulate afresh in the fibre, and then it will again contract. It is only by little and little that the fibre recovers its irritability. This truth, I dare venture to say, is as new as it is striking. It unfolds a vast number of phenomena hitherto inexplicable.” Here we have nothing but the pompous declaration of a fact already well known; viz. that not only a fibre, but the whole body, may be in a state of temporary insensibility, and yet recover either of itself or by the use of external means. How many people have fallen into a syncope, and yet recovered! How many limbs have become paralytic, and in time recovered their sense and motion! Yet this is all that we are informed of with so much parade and assumption of novelty. We know that when a person is in a faint he is insensible to ordinary stimuli, though very strong ones will rouse him; but what can we infer from this? Nothing; only we see it is so. Does it avail us any thing to be told that during the time of fainting the irritability is exhausted, and “in a short time the irritable principle will accumulate afresh;” in which case the patient will no doubt recover, unless he happens to be dead, which is the true meaning of an irreparable exhaustion of the irritability.

In speaking of the principle of irritability he expresses himself in the following manner. “I think that the oxygen is absorbed by the blood, and that the venous blood is oxygenated in the lungs during respiration. The most celebrated naturalists and chemists are of a different opinion: they think that the oxygen does not combine with the venous blood. According to them, this last loses carbon and hydrogen, and recovers the bright colour natural to it, without absorbing any thing from the atmosphere. . . . After having a long time attended the phenomena of respiration, and made many experiments upon this subject, I think it may be concluded that one part of the oxygen of the vital air combines with the venous blood, of which it changes the black colour, and makes it vermilion;[67] the second part of the oxygen unites with the carbon contained in the carbonic-hydrogen gas, which exhales from the venous blood, and forms carbonic acid air; a third part unites with the carbon of the mucus, contained in great quantities in the lungs, and which is continually decomposing; this part also forms carbonic acid air; a fourth part of the oxygen combines with the hydrogen of the blood to form water.”

On this theory I shall only observe, that though I lay claim to the former part, I allow the Doctor all the latter part to himself; particularly where he speaks of the formation of water to be exhaled during respiration. The air in question consists of two parts, like fixed air already mentioned. One of these is capable of being attracted, condensed, or united with certain substances; the other vanishes, leaving no other traces of its having ever existed, but heat, greater or less according to circumstances. When the air is taken into the blood, one part of it undoubtedly combines with something thrown out by the lungs, and forms fixed air, of which our breath contains a considerable quantity. We know certainly that the condensable part of fixed air is formed out of the condensable part of the oxygen, with certain additions. As therefore great part of this condensable oxygen is thrown out in fixed air at every expiration, it is natural to suppose that all of it is so: at least we cannot know the contrary without a series of very difficult and tedious experiments, which have never been made by Dr. Girtanner or any body else. But if the whole of this condensable part be thrown out, none can enter the blood by the breath; and consequently whatever true oxygen may afterwards be expelled from that fluid, must be a factitious substance, formed either during the artificial process, used for distilling it, or by a natural process In the body itself. It is not therefore at all probable that the oxygen which flesh emits in distillation can be derived from the air by respiration.

Another and more probable source is the food and drink we take; all of which are more or less impregnated with air of different kinds, particularly fixed air. This, we know, very readily condenses, and certainly will do so when taken into the body. In this state it not only may, but certainly will, pass into the blood, and through all the different parts of the body, until, having accomplished its purpose, whatever that may be, it is thrown out by insensible perspiration, as has been already explained.

The conclusions drawn by Dr. Girtanner from his experiments are, 1. That the change of colour which the blood undergoes during the circulation is not owing to its combination with hydrogen air[68]. 2. The deep colour of the blood in the veins is owing to the carbon it contains. 3. That the vermilion colour of the arterial blood proceeds from the oxygen with which the blood is conjoined during its passage through the lungs. 4. That respiration is a process exactly analogous to the combustion and oxydation of metals; that these phenomena are the same, and to be explained in the same manner. 5. That, during circulation, the blood loses its oxygen, and charges itself with carbonic hydrogen air, by means of a double affinity. 6. That, during the distribution of the oxygen through the system, the heat which was united with this oxygen escapes; hence the animal heat. 7. That the great capacity of arterial blood for heat is owing to the oxygen with which it is united in the lungs.

On these propositions, which constitute in a great measure the fundamental principles of the doctrine of oxygenation of the human body, we may remark,

1. Nobody can reasonably suppose that hydrogen air is the cause of the dark colour of the blood in the veins, because there is no source from which it can be derived; and, besides, it is certain that no kind of air can exist in its elastic state in the blood, without destroying the life of the animal. Some experiments proving this are given by Dr. Girtanner himself. It is true that an aerial vapour, of the nature of fixed air, exhales from the body by insensible perspiration; but there can be no doubt that this receives its elasticity only at the surface of the body, and is expelled the moment it is formed. It has indeed been proved, by undeniable experiment, that no air of any kind exists in the larger veins; because a portion of a vein, included between two ligatures, being cut out, and put under the receiver of an air-pump, does not swell in the least when the air is exhausted, which yet must be the case, did the smallest quantity of elastic air exist in it.[69]

2. When the Doctor asserts that the dark colour of the venous blood is owing to the carbon it contains, he is in the first place chargeable with the error of former chemists, who supposed that every thing which could be extracted from any substance by fire, existed previously in it, in that very form in which it is extracted by the fire; and in the second place he speaks entirely at random, without even a shadow of proof. Nay, he himself tells us, that he has repeated two of Dr. Priestley’s experiments, which in the clearest manner demonstrate, that neither the addition nor the abstraction of carbon, or any thing else, give this dark colour to the venous blood. “A small glass tube (says he) filled with arterial blood, of a bright vermilion, was sealed hermetically,[70] and exposed to the light. The blood changed its colour by degrees, and in six days became black as venous blood. The same experiment was repeated, with this difference only, that the tube was exposed to heat, and not to the light. The blood became black in a shorter time.” In these experiments it is plain, that if the blood contained oxygen at first, it did so at the last; the same with regard to carbon. How came it then to pass, that without either evaporation of the former, or addition of the latter, the change should be produced? If the oxygen imbibed by the blood in the lungs was sufficient to produce the red colour, why did it not preserve it? The case here is precisely similar to what happens with the calx of silver. When that metal is dissolved in aqua fortis, and again reduced to a solid form, it appears as a white powder, and will preserve its colour if carefully kept from the light; but if a vial be filled with it, and exposed to the sun, that side on which the light falls will in a short time become black, and this though the vial has been ever so carefully sealed.[71] Formerly, chemists had a method of accounting for this appearance, as well as that of the venous blood, by what they called the evolution of phlogiston: but now that the very existence of phlogiston is denied, we are deprived of this resource. But, whatever words we may use, it is plain that in neither case have we any ideas affixed to them which can make the matter at all more intelligible than it was before. But with regard to the blood, we are at a considerable loss to understand what the natural colour of it is; and indeed the question can only be determined by examining the blood of a fœtus which has never breathed. If the arterial blood of such a fœtus be of a dark colour, resembling that in the veins of a grown person, we must look upon this to be natural to it, and we may as well inquire why a rose is red, or an iris blue, as why the blood is of a dark, and not of a bright red. But, if we find this dark red change to a bright scarlet in the arteries, as soon as the child has breathed, we have as much reason to conclude that the air occasions this superior redness, as that an acid is the cause of a red colour in the syrup of violets, or an alkali of a green colour in the same. Experiments are yet wanting to determine this matter. Mr. Hunter has observed that “in such fœtuses as convert animal matter into nourishment, they most probably have it (the colour of the blood) influenced by the air, such as the chick in the egg, although not by means of the lungs of the chick, we find the blood, in the veins of their temporary lungs, of a florid colour, while it is dark in the arteries.”—The probability therefore is, that the blood is naturally dark; by the elastic principle of the oxygen that it is rendered brighter; and that, this elastic principle being expended in the course of circulation, the fluid reassumes its original colour.

3. Though enough has already been said to evince that the superior redness of the arterial blood is derived from oxygen gas, we shall still quote two instances from Mr. Hunter’s Treatise on the Blood, which set this forth in the clearest manner; and these instances are the more remarkable, because they demonstrate the phenomena not of the dead, but of the living body. 1. A gentleman in an apoplexy, who seemed to breathe with great difficulty, was bled in the temporal artery. The blood flowed very slowly, and for a long time. It was as dark as venous blood. He was relieved by the operation; but, on opening the same orifice in two hours, the blood flowed of the usual florid colour. 2. A lady in an apoplexy was treated in the same manner, and Mr. Hunter observed, that when she breathed freely, the blood from the temporal artery assumed a bright red colour; but when her breathing was become difficult, or when she seemed scarce to breathe at all, it resumed its dark colour, and this several times during the operation.

4. Respiration is not, as Dr. Girtanner says, a process similar to the combustion and oxydation (the calcination) of metals. Some of these by calcination, and all of them in the opinion of Dr. Girtanner, unite with the condensable part of the oxygen contained in the air, while the elastic part is dissipated in flame or heat. The reverse of this takes place in breathing; for here the elastic part of the oxygen unites with the blood, and makes it warm, while the condensable part, uniting with certain particles to be thrown off from the body, passes away in fixed air. Thus the process of respiraton does not resemble the calcination of a metal (at least according to our author’s opinion of that operation) but rather the inflammation of some combustible substance; for in both cases a certain quantity of carbon is found to be united with the basis of oxygen in the atmosphere, and thrown off from the place of combustion; and thus a quantity of fixed air is produced from every burning substance. Just so is it with respiration. If the condensable part of the oxygen combined with the blood, then no fixed air could be produced; or if any part of the oxygenous base was absorbed, it must certainly be known by a proportional deficiency in the quantity of fixed air produced. But there are no experiments made with accuracy sufficient to determine this point. It is true that many very able physiologists, as Borelli, Jurin, &c. have been of opinion, that part of the air is absorbed in respiration; but when we come to particulars nothing can be determined. Dr. Hales by experiment found the quantity absorbed to be a sixty-eighth part of the whole quantity inspired; but, on account of supposed errors, he states it only at an hundred and thirty-sixth part. Between these two the difference is so enormous, that we know not how to draw any conclusion from them. The French chemists are more decisive, and agree pretty well with one another. Chaptal calculates it at three hundred and fifty-three, and La Metherie at three hundred and sixty, cubic inches in an hour. Allowing these experiments to be just, the next question is, what part of the air is absorbed. Lavoisier says, that it is the oxygenous base, or the same with that which is absorbed in the calcination of mercury. But how comes he to know this? Surely not in the same way that he determines the absorption of it by mercury. In the latter case he takes a certain quantity of mercury, includes it in another known quantity of oxygen air, and heats the metal by means of a burning-glass or otherwise: the consequence is, that the air is absorbed, the mercury loses its fluidity, and is increased in weight. The metal gains the whole weight of the air absorbed; and, by another process, all the air and all the metal, or very nearly so, may be obtained in their original form. This experiment is so decisive, that nothing can be said against it with any shadow of reason; but who hath made, or who can make, similar experiments with the blood of a living man? Such experiments indeed might be made, if insensible perspiration did not stand in our way. Common atmospherical air is about eight hundred times lighter than water. A cubic inch of distilled water, according to Dr. Kirwan, weighs two hundred and fifty-three grains and a quarter. Oxygen air is somewhat lighter than common air: we shall therefore suppose that six hundred inches of it are equal to an inch of water. If then the blood absorb three hundred and sixty inches of air in one hour, it will in twenty-four hours have absorbed eight thousand six hundred and forty inches, equal in weight to fourteen inches of water and two fifths, which according to Dr. Kirwan’s estimate is between seven and eight ounces. But the quantity of matter insensibly perspired in that time is so much greater, that no calculation can be made. Here is one mode of determining the quantity of oxygen inspired totally impracticable in the human body, though quite easy and practicable in the case of mercury. The other mode of determining it by the expulsion of oxygen from the blood is equally impracticable. Dr. Girtanner indeed has expelled oxygen from flesh; but we know not in what proportion, nor can we determine whence it came. With regard to this last, indeed, there are two sources allowed by Drs. Beddoes and Girtanner themselves; viz. the absorption of oxygen by the lungs, and the quantity taken in with the aliment. A third source was also manifest from Dr. Girtanner’s experiments; viz. absorption from the atmosphere; for, by exposure to the atmosphere, flesh, which had once parted with its oxygen, became again impregnated with it. In this case therefore we must acknowledge that the uncertainty of the absorption by the lungs must be extremely great. A certain quantity of oxygen is undoubtedly thrown out in fixed air. How are we to determine this quantity? Certainly not by the first reverie that happens to occupy our imagination. It is a problem, the solution of which must be attended with the utmost difficulty. We must know, in the first place, how much oxygen was contained in the air inspired. In the second place we must know the quantity of fixed air expired. In the third place we must exactly know the proportion of oxygen contained in the fixed air thrown out by the breath. In the fourth place we must determine whether, by the conversion of oxygen into fixed air, any change is made in its bulk. For, if this shall be found to be the case, we should be led to suppose an absorption or augmentation of air when no such thing took place. This point therefore ought to be determined with the utmost accuracy. In the fifth place we must exactly know how much azote, septon, phlogisticated air is contained in the atmosphere inspired, and likewise in that expired. In the sixth place, we must be assured that there are no other fluids in the atmosphere capable of being absorbed by the lungs, excepting oxygen and azote. Whether there are any others or not, hath not been determined. From an expression of Dr. Fordyce, he would seem to be skeptical on the subject. “The atmosphere (says he) is found to consist of various vapours, of which air, or, as it has been called, pure air, or respirable air, (oxygen air) forms at present about a fourth. Gas (probably fixed air) forms some part;[72] but the greatest part consists of one or more vapours, which, without any positive quality, but from that indolence which makes mankind in their researches attempt to find a resting place, have been considered by many chemists as one individual species, under the names of phlogisticated air,” &c. In the seventh place we ought to know what quantity of pure oxygen, unconverted into fixed air, or whether any such, is thrown out by the breath. That a quantity of this kind of air is really thrown out, is probable, because we can blow up a fire with our breath, and by a blow-pipe excite a most intense heat, capable of melting the most refractory metals, platina excepted. It is true that the eolipile, by the mere conversion of water into steam, will blow up a fire also; though, if the access of external air be denied, the blast of the eolipile will put the fire out. Probably the breath would do the same; but even this cannot be accounted a decisive proof of the oxygen being totally exhausted; for the moist vapour with which the breath abounds may extinguish the fire, even though some small quantity of oxygen should remain in it. It is not, however, our business at present to enter minutely into such discussions. From what has been already said, it is evident, that the absorption of oxygen by the blood, instead of being indubitably established, is of all things the most uncertain; the requisites for determining it being absolutely beyond the investigation of any person, however accurate. We may indeed, with great labour and trouble, determine that some part of the air is absorbed in breathing; but what that part is, we are unable to discover from any chemical investigation. The opinion of the simplicity of metals, and their being reduced to a calx by the adhesion of oxygen, has been so implicitly, and in a manner universally, received, that it has given a new turn to physiology, so that, by a kind of analogical reasoning, the human body has been reduced to a mere chemical apparatus, the operations of which may be calculated as we can do the event of experiments in a laboratory. But, after a very long and tedious contest, Dr. Priestley seems at last to have overthrown this doctrine of oxygenation, even in the inanimate parts of the creation; so that we can much less apply it to the doctrines of life and animation. His experiments are published in the third number of the Medical Repository, volume II, and fully demonstrate, that, though mercury absorbs oxygen during calcination, this is not the case with all metals; that in many cases the oxygen will unite with other substances in preference to the metal, which last is nevertheless reduced to a calx as though it had united with the oxygen; that in many cases the addition of weight gained by the calx is owing to mere water, &c. He has likewise shown that phlogisticated air (azote) is not a simple substance, as has been taught by the new chemists, but consists, as well as fixed air, of an union of oxygen with carbon, or at least with the black matter of burnt bones, with which he made the experiment. These aerial fluids therefore being so easily convertible into one another, and the uncertainty of the changes in bulk which may occur in consequence of these conversions so great, it is impossible to say whether a portion of the atmosphere in substance, i. e. both oxygen and azote, is absorbed, as physicians formerly supposed; or whether a portion of oxygen air alone be absorbed, as Dr. Beddoes supposes; or whether only the elastic principle itself is absorbed, and the diminution in bulk made in consequence of the conversion of oxygen into fixed air; I say, these matters depend on circumstances so much beyond the reach of our senses, that if we come to any probable conclusion upon the subject, it must be by analogical reasoning from other known facts, not from experiments made directly upon the living body; which, in their own nature, must, always be extremely vague and uncertain.

5. That, during the circulation, the blood charges itself with carbonic hydrogen air, is an assertion which cannot be easily admitted. It has already been observed, that, by the air-pump, venous blood does not appear to contain any elastic fluid whatever; and it is also certain, that animals cannot bear any quantity of air injected into their veins. Dr. Girtanner himself tried several kinds, and all of them proved fatal. Having injected a considerable quantity of oxygen air into the jugular vein of a dog, the animal raised most terrible outcries, breathed very quickly, and with the utmost difficulty; by little and little his limbs became stiff, he fell asleep, and died in less than three minutes. On injecting into the vein of another dog a small quantity of phlogisticated air, the animal died in twenty seconds. With carbonic acid gas (fixed air) a third dog died in a quarter of an hour. A fourth was killed in six minutes by nitrous air.[73] From these experiments, had no others ever been made on the subject, it seems very probable, that no species of air can be safely admitted into the blood in its elastic state. If any such therefore should naturally be produced in the body, it must either be instantly thrown out, or disease must ensue. Such objections to the Doctor’s theory are so natural, that we might have thought he would have foreseen and provided against them. Instead of this he grounds the whole upon such slender evidence as could not be admitted in the most trifling matter. “An incision (says he) was made in the jugular vein of a sheep, and the blood which came from it was received into a bottle filled with nitrous air. When the bottle was half filled, it was closed. The blood coagulated immediately, and a separation of a great quantity of blackish serum took place. The day after, on opening the bottle, a very strong smell of nitrous ether (dulcified spirit of nitre) was perceived, the nitrous air having been changed in part into nitrous ether by the carbonic hydrogen gas of the blood. This experiment proves, beyond a doubt, that the venous blood contains carbonic hydrogen air; and that this air is not very intimately mixed with it, but may be expelled with the greatest ease.”

On reading the Doctor’s account of this experiment; it must be very obvious, that, however decidedly he may be of opinion that it proves beyond a doubt the existence of hydrogen air in the venous blood, yet there is not one solid reason; from what he says, for supposing any such thing. How can any man determine from the mere smell of sheep’s blood taken out of the body of the animal, and mixed with a poisonous vapour, what is the composition of human blood in the living body? In the case of any substance suspected to contain elastic air, the air-pump will always afford an experimentum crucis. But we know that venous blood does not yield any elastic vapour by the pump: if instead of blood, however; we should fill a portion of vein with beer, cyder, or other fermented liquor, it would instantly discover, by its swelling up, that it really contained air in an elastic state. If then from the tumefaction of the vein when filled with fermented liquor we conclude that the latter contains fixed air, why should we not, from the non-tumefaction of it when filled with blood, conclude that the vital fluid contains no air? If Dr. Girtanner was so well assured that the venous blood contains hydrogen air, he ought to have expelled some of it from a portion of the blood, noted the difference between the blood which had lost its air, and that which had not, and then, by adding the air to it again, restored the blood to its former state. Nothing less then recomposition can prove the truth of a chemical analysis; as division can only be proved by multiplication, or multiplication by division.

From all that has been said, we may fairly conclude, that no proof can be brought sufficient to prove the existence either of oxygen air or any other species of aerial fluid, in its elastic state, in the blood. Neither can we prove that any part of the condensable part of oxygen air is received by the breath in the lungs. It is, however, probable that this condensable part may be received into the stomach with our food; that having passed through the various channels of circulation, and arrived at last at the surface, it there resumes its aerial nature by combining with the superfluous heat of the body, and is evaporated through the pores of the skin by insensible perspiration. The aerial vapour which passes off by these pores indeed has been discovered to partake of the nature of fixed air; but we know that this species of gas always contains the basis of oxygen, being indeed composed of it; and whether the oxygen be taken into the body in its pure state or not, the result would undoubtedly be the same; for an union would be formed between it and the carbonic particles to be thrown off from the body. But thus we can never suppose the basis of oxygen or any other air to be a permanent part of the composition of our bodies; nor can the quantity of it be augmented by breathing any kind of air. The readiest way to increase the quantity seems to be by drinking fermented liquors. Thus, if the body is too hot, the superfluous heat will have a proper subject to act upon, viz. the condensable part of the fixed air; and hence we may perhaps account for the very grateful and cooling sensation produced by drinking these liquors in some diseases. With respect to the existence of carbon, charcoal or hydrogen in the blood, it is probable that it exists in equal quantity at all times, being indeed the fundamental material of the whole body, and probably only a modification of that dust from whence man was originally taken.[74] When the blood therefore grows very black, when the teeth are covered with a black sordes, the hands become foul, &c. we may say, indeed we too surely feel, that, in such cases, there is a propensity in the body to return to its original state of dissolution; but there is not one solid reason for supposing the proportion of its materials to be varied; that there is a collection of oxygen in one part, hydrogen in another, or in short that nature can admit of any such disproportion taking place.

6. We must now consider Dr. Girtanner’s account of the origin of animal heat, which is, that, “during the distribution of the oxygen through the system, the heat which was united with this oxygen escapes; hence the animal heat;” and, “that the great capacity of the arterial blood for heat is owing to the oxygen with which it is united in the lungs.”—This leads us to consider in a more particular manner the doctrine of heat, a subject hitherto much less investigated than the importance of the subject requires. What little we do know of this matter seems to be almost entirely owing to Dr. Black, who hath discovered some very remarkable phenomena unknown to former philosophers. His discovery here, as in that of fixed air, was accidental. Making experiments on the water of different temperatures, he found that the mixture would always be an arithmetical mean betwixt the two quantities mixed. Thus, on mixing water at 50 degrees with an equal quantity at 100, the temperature of the mixture would be 75 degrees; but if instead of using water only he took snow or ice for one of the quantities, the mixture was no longer an arithmetical mean betwixt the two temperatures, but greatly below it; so that a quantity of heat seemed to be totally lost and in a manner annihilated. His attention was engaged by this unexpected phenomenon, and, prosecuting his experiments, he found that, when water was converted into ice, it really became warmer than it was before; and, by keeping the fluid perfectly still during the time that cold was applied, he was able to cool it to 27 degrees of Fahrenheit’s thermometer, which is five degrees below the freezing point; but on shaking this water so cooled, it was instantly converted into ice, and the thermometer rose to 32. On reversing the experiment he found that mere fluidity in water is not sufficient to melt ice. A considerable degree of heat is necessary; and even when this is previously given to the water, the whole becomes as cold as ice by the time that the ice is melted. The result of his experiments in short was this: Water, when frozen, absorbs an hundred and thirty-five degrees of heat before its fluidity can be restored: that is, supposing a pound of ice at the temperature of 32 to be mixed with a pound of water at the temperature of 32, by adding 135 degrees, so that the temperature of the water is augmented to 167, the ice will indeed be melted, but the temperature of the whole quantity of liquid will be reduced to 32. In this case therefore the heat manifestly assumes two different modes of action: one in which it acts internally upon the substance of the body, without being sensible to the touch, while in its other state it hath no effect upon the internal parts, but affects bodies on the outside. The former state therefore the Doctor distinguished by the name of latent, the latter by that of sensible heat.

The same theory was applied to explain the doctrine of evaporation, and that in the most decisive and satisfactory manner. The Doctor found, that, in the distillation of water, much more heat was communicated to that in the worm-tub of the still, than could be supposed necessary to raise the water distilled to 212 degrees, which is the utmost that water can bear. In prosecuting the experiment he found the quantity of heat absorbed by the water, when raised into vapour, truly surprising; no less than a thousand degrees; an heat more than sufficient to have made the whole quantity of fluid that came over red hot. Some objections, however, were made to this theory, even by the Doctor’s friends. Mr. Watt, particularly, though he could not deny the theory derived from Dr. Black’s experiments, yet suggested one, which, had it proved successful, would have overthrown the whole. It was this: Let water be distilled in vacuo, where it boils with a heat of 97 degrees, and the operation must be carried on with much less fuel, and with much greater ease, than in the common mode. It was said that, in this experiment, Dr. Black was equally concerned with Mr. Watt; but, in a personal conversation with the Doctor himself, he assured me that he had no farther concern than foretelling that the experiment would not succeed, which it seems did not. The event was as follows: Mr. Watt, determining at all events to try the experiment, caused to be made a copper retort and receiver, joined together in one piece. In the receiver he pierced a small hole, and, heating both retort and receiver, plunged the latter into cold water. The consequence was, that a considerable quantity of water entered the vessel, and was easily poured back into the retort, as a subject for distillation. A fire being now applied, the water was soon raised into steam, which filled both retort and receiver, and in a great measure expelled the external air. The small orifice in the receiver being now closed, and the receiver itself plunged into cold water, the distillation went on in vacuo; for, as soon as any of the steam was condensed, the space which it had occupied (according to Dr. Black one thousand and sixty-six times more than the original water) was become absolutely empty, and more steam, rarefied, not by any quantity of sensible heat, but merely by that which it contained in a latent state, would occupy the place of the former. The event of the experiment showed the truth of Dr. Black’s theory. The water boiled, and steam was raised as well as if access had been given to the air; but with this difference, that the upper part of the distilling vessel was never heated above what the hand could easily bear. With the water in the cooler it was quite otherwise. It became hot as usual, and, by the quantity of heat it received, plainly demonstrated that the vapour, though destitute of most of its sensible heat, yet contained an immense quantity in a latent state. The saving of fuel therefore in the practice of distillation, which was Mr. Watt’s object in making the experiment, was quite trifling, and not equal to the trouble of filling the retort with liquid.

The doctrine of latent heat thus established, furnished a solution of many phenomena which could not formerly be explained in a satisfactory manner. Thus the melting of all kinds of substances was found to be owing to an absorption of heat, while their condensation was attended with the contrary. Fluidity in all cases was explained on the same principle; and the more heat that was absorbed, the more fluid the matter became. Thus water, when in a condensed or solid state, absorbs 135 degrees of heat before it becomes fluid. A thousand degrees more convert it into vapour, and at last, by passing through the intense heat of a glass-house furnace, it is converted into a brilliant flame, and augments the heat of the furnace to a great degree. Hence the practice in glass-houses of throwing water into the ash-hole, the vapour of which, by passing through the burning fuel, makes the furnace much hotter than it was. In a similar manner were explained the phenomena of crystallization, the ductility of metals, the heat produced by hammering them, and the hardness produced by the operation, as well as the operation of annealing, &c. One other phenomenon, a very curious one, shall be noticed, on account of its being connected with the subject of this treatise. It is this: Let a small vessel filled with vitriolic ether be put into a larger one of water, and both included in the receiver of an air-pump. On exhausting the air, the ether boils, and is converted into vapour, while the water freezes. This shows that heat does not always act equally upon surrounding bodies, but has a tendency to enter some in preference to others; and from other experiments it appears, that this property has a considerable connexion with the density of the bodies concerned.

Thus one step was gained, and it was universally admitted that heat, in some cases, entered bodies, and in others was thrown out of them; but now the question arose, What is heat; and by what laws is it regulated, or from what source is it derived? Here Dr. Black himself was at a loss; for, as he supposed cold to be a mere non-entity, and only to consist in a comparatively smaller degree of heat, some phenomena occurred which would not easily admit of solution upon such an hypothesis. With these Dr. Black did not meddle much, but others were bolder. Dr. Irving, Professor of Chemistry at Glasgow, undertook to explain the whole mystery of latent heat upon the single principle of attraction. One of the most puzzling phenomena in the way of Dr. Black’s theory had been, that in some cases heat and cold seemed to repel each other, and a very remarkable instance of this was, that, in the morning, a little before sunrise, when the rays of light pass through the atmosphere, a little above the surface of the earth, the air then becomes manifestly colder than even at midnight. Dr. Irving’s explanation of this was, that the sun’s rays attracted heat from the atmosphere, and thus rendered it colder. Such at least was the explanation given in an inaugural dissertation by Dr. Cleghorn, one of Dr. Irving’s scholars; for the Doctor himself delivered his opinions only to them. In other cases he supposed that different substances had different capacities for receiving heat; and, of consequence, should the form, or rather the internal constitution, of the body be changed, the capacity of it for receiving heat must also be changed; and as an attraction subsists, or is supposed to subsist, between heat and all other substances, it is plain that while this attraction subsists, if the capacity of any substance for receiving heat be augmented, it will imbibe much more than it would have done had its former constitution remained. Thus water in its liquid state contains a certain quantity of heat; we may therefore say that water has a capacity for receiving heat equal to one to ten, or what we please. Vapour has a capacity for containing heat ten times greater than water. Water therefore, when converted into vapour, will imbibe ten times the quantity of heat that the water contains; and, again, on being re-converted into water, the capacity becoming what it was before, the superfluous quantity must be thrown out, as in Dr. Black’s experiments. In like manner, when a metal is melted by the fire, the capacity of it for receiving heat is changed: of consequence a great quantity is imbibed, and again expelled by the change of capacity which takes place on its becoming solid; and thus, from the change of capacity, in different substances, every phenomenon was solved.

This doctrine of capacities did not give general satisfaction. Dr. Black himself said of it, that it was neither probable nor ingenious;[75] notwithstanding which, it continued to be received, and even very generally adopted. Dr. Crawford, so well known for his writings on this subject, has adopted the idea, and Dr. Girtanner, in the passage above quoted from him, appears to be of the same opinion. The doctrine, however, had several opponents, among whom were the Monthly Reviewers. In their account of Nicholson’s First Principles of Chemistry, they express themselves in the following manner: “We only wish, that, in the doctrine of heat, he had avoided, which he might easily have done, Dr. Crawford’s idea of bodies having different capacities for heat. In the melting of ice, for instance, a quantity of heat is absorbed, without any increase of the temperature, that is, without making the water sensibly warmer than the ice before its liquefaction; which is said to be owing to the water having a greater capacity for heat, or being able to hold more of it, than the ice; and, in like manner, when converted into vapour, its capacity is further increased, or it can hold more still. This appears to us a very unchemical, and a very inadequate idea of the matter: for, admitting water to have a greater capacity than ice, how is the change from one state to the other to be effected? Can the properties which a body is found to possess, after a change has taken place, be assigned as a cause of the change itself? Or will it be said, that the heat first enlarges the capacity, and then hides itself in that capacity so enlarged? We should think it much better to say, consonantly with the phenomena of other combinations in chemistry, that a certain quantity of heat, uniting with the ice, first liquefies it, as a certain quantity of acid only neutralizes an alkali; that if any surplus quantity must be introduced, that surplus, remaining free and uncombined, must act and be sensible as heat in the one case, and acid other; and that different bodies require different quantities of heat or acid to be combined with them, for producing the changes in question.”[76]

Thus the Reviewers, as well as others, reasoned a priori, and several facts were adduced to prove that no such changes in capacity could take place. But however strong the arguments adduced, or however plain the experiments might be, little or no notice was taken of them, and the enlargement or diminution of capacities has been repeated, seemingly by rote, from one author to another, without the least inquiry or investigation. Dr. Girtanner indeed says that “the oxygen united with the arterial blood in the lungs” is the cause of the great capacity of the arterial blood for heat. But this is assigning a very doubtful cause for a very doubtful effect. He ought to have proved in the first place that arterial blood really has this capacity; for its being hotter than the blood of the veins, only shews that it parts with more heat to surrounding bodies than venous blood does; which is a proof that it contains less heat, if there be any difference, than that of the veins. But the truth is, that the capacity for containing heat depends neither on the oxygenation nor hydrogenation of a fluid, but upon its density. The more fluid and the more easily expansible into vapour that any substance is, the greater quantity of heat it is capable of containing, and vice versa. This has been fully ascertained by Mr. William Jones, an English clergyman, whose observations on the generally received system of philosophy contain many particulars worthy of attention. From his experiments it appears that a piece of red-hot iron, thrown into water, imparts much less sensible heat to it, and is itself much more effectually quenched, than by throwing it into an equal quantity of quick-silver of the same temperature with the water. As the quick-silver therefore becomes much hotter to the touch than water does upon throwing a piece of red-hot iron into it, and as the iron itself is much more imperfectly quenched by the metal than by the water, it follows that the latter is capable of containing much more heat than the former. But such experiments are not applicable to the blood. Though that of the arteries may be somewhat hotter than the venous blood, yet the reason is obvious. The heat is communicated directly to the arterial blood in the lungs; but during the circulation a part of it evaporates, and the farther distant any part is from the lungs, the more cool will the vital fluid be, without regard to any alteration of capacity, which indeed never can be shown to exist.

But the most decisive experiments against any supposed alteration in the capacities of bodies for containing heat are those lately tried by Count Rumford, and related in the Philosophical Transactions for 1798. His attention to this subject was engaged by observing the great degree of heat acquired by a brass gun during the time of boring it,[77] and still more by the intense heat (much greater than that of boiling water) of the metallic chips separated from it by the borer. From a consideration of these things he was naturally led to the following inquiries. “Whence comes the heat actually produced in this mechanical operation? Is it furnished by the metallic chips which are separated by the borer from the solid mass of metal? If this were the case, then, according to the modern doctrine of caloric, the capacity for heat of the parts of the metal so reduced to chips, ought not only to be changed, but the change undergone by them be sufficiently great to account for all the heat produced. But no such change had taken place; for I found, that by taking equal quantities by weight of these chips, and of thin slips of the same block of metal, separated by means of a fine saw, and putting them at the same temperature, that of boiling water, and putting them into equal quantities of cold water (that is to say, at 59 1/2 of Fahrenheit) the portion of water into which the chips were put, was not, to all appearance, heated either less or more than the other portion in which the chips were put.”

From this experiment, several times repeated with the same result, Count Rumford inferred, that the heat could not possibly have been furnished at the expense of the latent heat of the metallic chips. He then proceeded to ascertain “how much heat was actually generated by friction, when a blunt steel borer being so forcibly shoved (by means of a strong screw) against the bottom of the bore of the cylinder, [of the machine in use] that the pressure against it was equal to the weight of about ten thousand lb. avoirdupois, the cylinder being turned round on its axis (by the power of horses) at the rate of about thirty-two times in a minute.” In this experiment the metallic dust or scaly matter detached from the cylinder by the borer weighed only 837 grains troy; but, says the author, “Is it possible that the very considerable quantity of heat produced in this experiment (a quantity which actually raised the temperature of above 113 lb. of gun-metal at least 70 degrees of Fahrenheit’s thermometer, and which of course would have been capable of melting 6 1/2 lbs. of ice, or making near five pounds of ice-cold water to boil) could have been furnished by so inconsiderable a quantity of metallic dust, and this merely in consequence of a change of its capacity for heat? As the weight of this metallic dust (837 grains troy) amounted to no more than one 948th part of that of the cylinder, it must have lost no less than 948 degrees of heat to have been able to raise the temperature of the cylinder one degree; and consequently it must have given off more than sixty-six thousand, three hundred and sixty degrees of heat to have produced the effects which were actually found to have been produced in this experiment.”

It was next considered whether the air did not contribute to the generation of this heat; and our author determined that this could not be the case; because the quantity of heat generated was not sensibly diminished when the free access of air was prevented. From another experiment it appeared that the generation of the heat was neither prevented nor retarded by keeping the apparatus immersed in water. Here the friction generated so much heat, that in one hour the temperature of the water surrounding the cylinder was raised from 60 to 107 degrees of Fahrenheit. In half an hour more it was raised to 142; at the end of two hours to 178; at two hours 20 minutes to 200; and in two hours and a half it boiled.[78] On the whole, Count Rumford concludes, that “the quantity of heat, produced equably by the friction of the blunt borer against the bottom of the hollow metallic cylinder, was greater than that produced equably in the combustion of nine wax candles, each three quarters of an inch diameter, all burning at the same time with a clear, bright flame.” From all these experiments, however, our author does not draw any certain conclusion. “What is heat? (says he.) Is there any such thing as an igneous fluid? Is there any thing that can with propriety be called caloric? The heat produced, in the author’s experiments, by the friction of two metallic surfaces, was not furnished by small particles of metal, detached from the larger solid on their being rubbed together. It was not supplied by the air, because the machinery in three experiments was kept under water, and the access of atmospherical air completely prevented. It was not furnished by the water which surrounded the machinery, because this water was continually receiving heat from the machinery and could not at the same time be giving to and receiving heat from the same body; and because there was no chemical decomposition of any part of this water.” At last he observes, that the source of this heat, whatever it is, must evidently be inexhaustible, adding, that “any thing, which any insulated body, or system of bodies, can continue to furnish without limitation, cannot possibly be a material substance; and it appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of any thing capable of being excited and communicated, in the manner the heat was excited and communicated in these experiments, except it be MOTION.”

On this last paragraph, however, it is obvious to remark, that the whole force of the argument rests upon an insinuation, that the cylinder and borer were insulated, or cut off from all communication with any other material substance. Had this been the case, then no doubt it would follow that an endless supply of any thing material could not be furnished by them; but if, as Dr. Boerhaave and many other learned and intelligent persons have supposed, fire be an element universally present, and which becomes sensible to the touch only in consequence of a particular mode of action, it will follow, that no substance in nature can be insulated with respect to it; but, in whatever place, and for whatever length of time, any substance shall be affected in such a manner as to agitate this fluid, there we shall perceive a production of heat without limitation, even though heat itself be no more than the action of a fluid essentially material, though invisible to us.

Considerations of this kind occurred long ago to the writer of this treatise, when by the nature of his employment it was necessary for him to speculate upon these subjects. It could not then but appear to him that the theory of Dr. Black was far superior to any that had been published. The opinion of those who supposed fire to consist in the vibratory motion of the particles of solid bodies, seemed altogether untenable. It is impossible to explain the phenomena of heat upon ordinary mechanical principles, because, with respect to all terrestrial substances, heat constantly appears as an agent, while they are merely passive; and no man can explain the nature of a cause from its effect. Thus one of the most obvious effects of heat is expansion, or enlargement of bulk, in such bodies as are heated. But if from this fact we infer that the parts of elementary fire are repulsive of one another, our reasoning is certainly erroneous. In like manner, when we are not sensible of heat, we are not authorised to conclude that it is not present; for Dr. Black has demonstrated that it may be present in very great quantity, though indiscoverable either by our senses or by a thermometer.

But, with regard to the theory published by Dr. Black himself, it is evident that, though one part of it rests on the solid basis of experiment, the other is founded entirely upon hypothesis, and that too an hypothesis which cannot admit of being proved by any experiment, viz. that cold is a mere negative, and hath no real existence in nature. Among many phenomena which militate against this opinion, the following experiment of M. Geoffrey seems to be the most remarkable. He took a small bason filled with water, and set it on a support in the middle of a large tub of water, in such a manner that the temperature of the water in the tub might communicate itself to that in the bason. This being ascertained by a thermometer placed in the bason, he threw a quantity of burning coals into the tub. The effect of this, on the supposition that cold is a mere privation of heat, ought to have been, that the heat of the coals, communicated to the water in the large tub, would in a short time pervade the small bason, and affect the thermometer there. The latter would therefore rise; but instead of this it fell several degrees before it began to rise; for which it doth not appear that any other reason can be assigned than that the cold is partly repelled by the heat of the coals, and therefore, entering into the small bason of water, it causes the thermometer to sink previous to its rising. To the same purpose we may urge the phenomenon already taken notice of, viz. that the sun’s rays, when passing at some distance above the surface of the earth, cool the lower part of the atmosphere. The natural solution is, that the heat of the sun partly repels the cold downwards; and as for the doctrine of attracting heat from the atmosphere, Count Rumford has shown that this does not happen in a case where we might with much more probability expect it; not to mention the violence done to the common perceptions of mankind by supposing the sun’s rays, which are most evidently the source of heat, to have any occasion to attract heat from the atmosphere or any thing else.

Lastly, with regard to the capacities of bodies for containing heat, the doctrine appears to involve a radical error, of such enormous magnitude, that it is impossible to make any thing of it. This is no less than confounding the heat which flows out from bodies with that which they contain as an essential part of their composition, and which they cannot emit without being changed into some other form. Thus the capacity of aqueous vapour for containing heat, according to Dr. Black, is 1000 degrees; yet without decomposing the vapour it would have been impossible to have known this; for vapour is often extremely cold to the touch, and a thermometer immersed in it will sink greatly. In short, all that we can know about the capacity of bodies for retaining heat is, that they either continue to absorb it, or we may continue to force it into them, till they be reduced to vapour. It is doubtful whether they can receive more; for from the experiment with Papin’s digester, formerly mentioned, it appears that the additional quantity of heat, which the water was made to receive, very quickly left it as soon as the steam had room to expand.

But, to come to a conclusion upon this subject: If we will investigate the nature of heat, we must do it as in other cases, viz. by making the igneous fluid, caloric, or what we please to call it, the object of our senses; for we cannot reason fairly, or indeed come to any rational conclusion at all, by doing otherwise. In this investigation it is necessary to attend to the particulars mentioned by Count Rumford. The fluid must be omnipresent in its nature, infinite in its quantity, and equable, uniform and incessant in its action; as far as these epithets can be applied to any material being. There are only two fluids which we know that can answer to these characteristics. The one is the light of the sun, which pervades all the celestial spaces; the other the electric fluid, which penetrates every terrestrial substance. Both of these produce heat, unlimited in quantity, as well as in duration, provided their action be continually kept up. The mode in which both produce heat is exactly the same, viz. by converging into a focus; and the greater the quantity, the greater is the heat, and that without any limitation either as to intensity or duration. With regard to the solar rays, it has long been known that by concentration they would produce heat; nevertheless it was unaccountably doubted whether the rays themselves were the matter of heat. One objection to this was, that on the tops of high mountains the air is exceedingly cold, though the sun shines very bright. But this objection was founded upon an erroneous notion that, wherever the matter of heat exists, there we must feel it; which doth not follow any more than that wherever air exists there we must feel a wind blowing upon us. Wind is air in motion, and heat is a more subtile fluid in motion. One demonstration of this is, that, on the tops of the highest mountains, a burning lens or mirror will set fire to combustible bodies as readily as in the vallies at the foot of them. Neither has heat, properly so called, anything to do with air. The focus of a burning-glass will heat bodies in vacuo as well as in the open air; and Sir Isaac Newton has observed, that if a thermometer be included in the vacuum of an air-pump, it will acquire the temperature of the room nearly in the same time that another will when included in a similar glass without any exhaustion.

The science of electricity is but of late date; and most violent and hypothetical disputes have taken place concerning the nature of the fluid. Its luminous and burning properties naturally led a number of people to suppose that it was elementary fire; but this was opposed by others with as much violence as if there had been something criminal in the supposition. The opposition, however, was founded upon the same error with that about the solar light. It was imagined that wherever elementary fire existed, there heat must be felt; and it was especially urged, that electricity, though it produced light, did not produce any heat, except when it exploded with such violence as to penetrate the internal substance of bodies, agitating their particles, and by this agitation producing heat. It has now, however, been found, that the electric aura, as it is called, when made to converge in great quantity to the point of a needle, will heat it to such a degree as to set fire to gun-powder. This shows that heat is occasioned by the convergence of this fluid to a focus, and to its divergence from it. In the focal point, heat will always take place. From the experiments of Hauksbee, Beccaria and Priestley, it likewise appears, that electricity will render transparent the most opaque bodies, such as sealing-wax, pitch, &c. which even the most intense light of the sun cannot do. As to the intensity of the heat produced by it, experiments have shown, that it cannot be exceeded even by that of the most powerful mirror. Globules of gold have been vitrified, platina melted, and the most infusible substances reduced to glass, by means of the electric shock. From so many evidences, therefore, it appears to me impossible to conclude otherwise than that the light of the sun and the electric fluid are the same thing; and, according to the different modes in which they act, they produce the phenomena of heat and light in all their varieties, besides a multitude of other effects of which we cannot have any perception. We may indeed, if we please, suppose that some other thing exists which is heat itself, and that the light or electric fluid sets in motion, attracts, repels, or acts otherwise upon this unknown something; just as it comes into our heads to fabricate our system. But, until our senses can discover in some way or other this hidden substance, reason will always suggest that it has no existence. We may say that without such a supposition we cannot solve the phenomena of heat. But do we ever expect to solve these phenomena; or do we know all that the solar light and electric fluid can perform? If we do not know what they can do, neither do we know what they cannot; and the invention of other fluids must be accounted not only chimerical but useless.

But, to be more particular: on the subject of heat people have embarrassed themselves more with philosophical reveries than by any real difficulty, and rendered the matter more obscure than nature has made it. We have already observed, that by the convergence of light, or of electricity, heat is always produced. Here we can see the mode in which the fluid acts, viz. first by converging, and then diverging. When the light falls upon a solid body, it is evident, that if it be allowed to flow out as easily as it flows in, no internal agitation of the parts, or of any fluid contained in them, can take place. Transparent bodies therefore are never heated. Again, if the light be not allowed to enter the substance of a body, but is entirely reflected, the body cannot be heated; and hence it is very difficult to melt a polished metal even by a strong burning-glass. M. Macquer’s burning mirror, which vitrified flints, could not melt silver. But, when the light falls upon a body capable of allowing it to enter its substance, at the same time that it cannot get out without difficulty, it is plain that the force of the fluid will be exerted in order to overcome that difficulty; the body will be expanded in all directions; the fluid will be thrown out in the same manner, and the more that the internal action of the light prevails over that power by which the parts of the body cohere, the more will the phenomena of heat be perceptible.

Again, let us suppose that the etherial fluid enters the substance of any body capable of being dilated to a great degree, it is equally plain that the action of the fluid must for some time be directed only upon the internal parts, and consequently will be imperceptible on the outside. This then is called latent heat; and where the pressure on the outside balances that on the inside no heat will be perceptible to the touch. But by whatever means this balance is broken, heat will instantly be perceptible; and experiments show that the balance may be broken either by an increase of cold or heat. Thus, in the case of water, the internal pressure remains equal to the external, until the fluid is cooled to a few degrees below 32. The balance is then broken, and the internal action prevails; a quantity of what is called sensible heat escapes, and the water is converted into ice. Again, at the temperature of 32, little or none of the water evaporates; but by the addition of heat, by which the internal action of the subtile fluid we speak of becomes greater than the external, the water is converted into vapour; and it is remarkable that the same effect takes place on greatly augmenting the degree of cold; for the evaporation from ice, even in frosty weather, is found to be very considerable.

On the whole, from innumerable experiments it appears, that there exists in nature a certain invisible fluid, by the action of which, when diverging from a centre, heat is produced in the central point. By a certain other power this diverging force is limited, so that in some cases it is not perceptible beyond the surface of the body in which it acts, and then it is called latent heat. In other cases it is perceptible in a certain degree, and the degree in which it is perceptible hath been called the temperature or sensible heat of the body. On mixing different substances together it is found, that very often the proportions between the external and internal actions are varied. This has been already observed, when giving an account of Dr. Black’s discovery of latent heat, viz. that when snow and warm water are mixed together the temperature of the mixture differs very considerably from the arithmetical mean between the temperatures of the two substances employed. Dr. Crawford prosecuted the experiment further, and found that there were few substances which, on being mixed, did not shew a temperature different from that of the arithmetical mean between the temperatures of the two originally employed. This difference he unfortunately used as the foundation of a rule for determining the capacities of different substances for containing heat, and upon this erroneous principle has raised a superstructure, which upon no occasion can be of service to science, but must always produce obscurity and confusion wherever it is introduced.

With regard to the power which sets bounds to the expansion of the fluid acting as heat, it is natural to think that it can be no other than the same fluid acting in a contrary direction, or from a circumference towards a centre; and thus we shall always find that the same fluid, by limiting its own operations, may produce those phenomena which have been hitherto deemed so difficult of explanation. In what manner this limitation is in all cases effected, or indeed in any case, we cannot pretend to explain. It is sufficient to observe, that wherever there is a perpetual efflux of any thing, there must be also a perpetual influx at the same time, and in proportion to the one the other will be. These two are directly contrary to one another, and, as we suppose the fluid to be universal, it is evident, that if any part of it be put in motion in a particular direction, the rest will press towards that part where the motion is, in order to keep up the equilibrium. Hence we may easily account for the heat produced by percussion or by friction. By hammering a piece of iron, as Dr. Black justly observes, the fluid is forced out from between the parts of the metal. The emission of this fluid in all directions is heat itself; and no sooner is one quantity thrown out than another supplies its place with great rapidity, and so on, until the pressure of the rest in some way or other counteracts the emission of any more, and the heat ceases. Just so with friction. The heat produced by it is always in proportion to the pressure employed. By this pressure the parts of the two substances are forced into such close contact, that an agitation and emission of the fluid pervading their substance takes place. This agitation, as we have already noticed, is heat itself, and, as long as the friction is continued, more and more heat will be produced, without any limitation, as Count Rumford has observed.

Some bodies have a greater disposition than others to emit this subtile fluid; and these we say are naturally of a warmer temperature than others. The temperature is nothing else than the efflux of the fluid from them, continually kept up by the action of the surrounding fluid. By mixture with different substances the temperatures of various bodies may be changed; by some the influx, and by others the efflux, may be augmented. In the former case we say the body becomes colder, in the latter hotter, than before; and in not a few cases the agitation of the fluid becomes so great that the matter actually takes fire. In all these cases, however, we can discover nothing more than the bare fact, that so and so is the case. We know that the bodies do grow hot by the convergence of the etherial fluid towards them, and its emission from them; but why it should converge or diverge we know not.

Thus much with regard to heat in general. We must next consider another fluid which has very generally been accounted the source and fountain of heat, viz. air. This is indeed so much the source of heat in all our operations, that it was natural to think it the only one; but experiments have now determined that air itself is a mere creature of heat and light;[79] for, by employing these in a proper manner, airs or gases of all kinds have been produced. Thus, by exposing water in a glass vessel for some time to the rays of the sun, a quantity of very pure oxygen air may be obtained; by concentrating the sun’s rays upon charcoal, inflammable air may be had; and by distilling, with a strong heat, substances of various kinds, we may obtain a great variety of aerial vapours. From all this we may reasonably conclude that heat, attached to some other substance, dissolved in it in such a manner as to become invisible, forms the substance of air. Heat therefore being the agent in the composition of air, it is reasonable to suppose that it is the agent in its decomposition also, or in its transformation from one species to another, of which the conversion of oxygen into fixed air by combustion is an instance. When air is taken into the lungs the blood is warmed by the action of that invisible fluid, which has already given elasticity to the air. In consequence of a considerable quantity of this fluid being then converted from a latent into a sensible state, part of the elastic principle must be lost, and the air diminished in bulk. The reason why this must constantly take place is, that part of the heat evaporates from the surface of the body, during the course of circulation. Were it not so, the quantity thrown out by the lungs would be exactly equal to that which the blood received, and consequently there could be no diminution between the bulk of the air expired and that which was inspired; but, on account of the waste just mentioned, the blood must always receive somewhat more than it gives out by the breath. Thus, while the air we breathe continues the same, and the organization of the body is not changed, the natural operations will go on smoothly, and health will continue; but, as we have formerly observed, by an alteration of either of these, disease must ensue; and we must now endeavour, from the principles laid down, to examine the mode in which epidemic diseases, and particularly the plague, may be produced.

The air is so evidently connected with human life, that it has been from the earliest ages accounted the source of pestilential diseases, though, as none of the more obvious qualities of it, such as heat, cold, moisture, or dryness, appeared to be connected with them, they were generally supposed to proceed from the action of some unknown natural cause, or from that of the Deity himself. Some, however, have also been of opinion that plagues might originate from the obvious qualities of the air in conjunction with certain effluvia from putrid vegetable or animal bodies. Thus, in several plagues mentioned in ancient history, we find swarms of dead locusts, grasshoppers, the carcases of those slain in battle, crowded houses, and filth of all kinds, assigned as causes. This opinion was adopted by Dr. Mead, and he gives the following account of the origin of the plague in Egypt. “Grand Cairo is crowded with inhabitants, who for the most part live very poorly and nastily; the streets are narrow and close; it is situate in a sandy plain, at the foot of a mountain, which, by keeping off the winds that would refresh the air, makes the heats very stifling. Through the midst of the city passes a great canal, which is filled with water at the overflowing of the Nile; and, after the river decreases, is gradually dried up: into this canal the people throw all manner of carrion, filth, &c. so that the stench which arises from this and the mud together is insufferably offensive. In this posture of things, the plague every year preys upon the inhabitants, and is only stopped when the Nile, by overflowing, washes away this load of filth; the cold winds, which set in at the same time, lending their assistance by purifying the air.” He then proceeds to account for the plagues in Ethiopia in the manner above related, viz. by the prodigious swarms of locusts, which sometimes occasion a famine by devouring the fruits of the earth, and, when they happen to be cast by the winds into the sea, occasion a pestilence; the putrefaction being heightened by the intemperance of the climate, which here is so great that it is infested with violent rains for three or four months together; and it is particularly observed of this country, that the plague usually invades it whenever rains fall during the sultry heats of July and August. He next takes notice of what the Arabians say of the origin of the plague in Ethiopia, viz. that it is brought on by unseasonable moistures, heats, and want of winds. But, whatever truth may be in the account given of the Ethiopic plagues, the testimonies already produced in this treatise are sufficient to render it very doubtful, at least, whether the plague ever does originate in Cairo, or any other place in Egypt. Besides, if we once admit the existence of any thing as a cause adequate to the production of a certain effect, wherever that cause exists the effect ought certainly to follow, unless where we plainly perceive something which prevents its action. It is not fair reasoning to say that the action of the cause is prevented by something unknown, for we might as well say that this unknown something is the cause originally, and acts only upon certain occasions, of when it thinks proper. Now, if the filth of the canal of Cairo be the cause of the plague in that city, it ought to recur annually at the season when that filth exists in greatest quantity, and in the most putrid slate. Nevertheless we have the express testimony of Mr. Eyles Irwin, that at the time he was in Cairo there had not been any plague for seven years. The account he gives of it is a kind of contrast to that above quoted from Dr. Mead. “Misir al Kaira, says he, or the City of Anguish, so called from the frequent visits which it has received from the plague, but commonly called Grand Cairo by us, is situated in lat. 30 degrees 3 minutes N. on an artificial branch of the Nile. Old Cairo nearly faces the river; but the new city is removed above a mile from it, and approaches to the range of mountains which runs through Upper Egypt, and abruptly breaks off here. It is undoubtedly one of the finest cities in the east; which, from the present style of architecture that reigns among the orientals, is but a faint commendation. The houses are in general built of stone, and, being elevated to several stories, would make a grand appearance, notwithstanding the inelegance of their structure, were not the effect destroyed by the excessive narrowness of the streets. This is one of the causes to which the ingenious Dr. Mead ascribes the birth of the plague in this capital; but experience evinces that it arises from foreign and adventitious causes. There has not been a plague here these seven years; which is rendered more remarkable by the commencement of the Russian war at the date of its cessation. No one can account for this; though a year seldom passed by before without a visit from it.”[80]

From this it plainly appears, that, however these putrid effluvia may concur with other circumstances in producing the plague, they are by no means the only cause; otherwise not a single year could have passed in Cairo without a pestilence; and the very same thing we shall find to hold good in every other, let us choose for a cause what we will. In order to investigate this matter fully, we must now consider what causes have been assigned by physicians for other epidemical diseases; and here, to avoid prolixity, we shall chiefly confine ourselves to those enumerated by Dr. Fordyce as the causes of fever; a gentleman whose very extensive experience must give the greatest weight to his testimony.[81] The principal causes assigned by him are,

1. Infection, or “a peculiar matter generated in the body of a man in fever, which is carried by the atmosphere, and applied to some part of the body of a person in health, and which causes fever to take place in him.” That such a cause exists, he proves from observing that “of any number of men, one half of whom go near a person ill of a fever, and the other half do not, a greater number of the former will be infected, in a short period afterwards, than in those who do not.” He says he has known, in such circumstances, seven out of nine infected with the disease. This infection is not discoverable by smell or any other organ of sense; neither can the greatest attention to cleanliness disarm it of its malignity. Of this the Doctor says that he has known instances; nay, of a person going into a room where a feverish patient was, and bringing with him the infection, which was communicated to others in the room to which he came. He owns, however, that by allowing the air to stagnate in which feverish patients are, the infection will become extremely violent and fatal. This may naturally be supposed, even without having recourse to putrid effluvia; because, independent of these, the imperceptible infectious matter itself will undoubtedly be accumulated in the atmosphere of the room, and act more powerfully than it could have done had it been partly carried off and diluted by attention to cleanliness and ventilation. He also says, that “when a number of persons live in a small space, supposing even that they are kept as clean as possible, it happens frequently that fever arises in some, often in many of them. It has been in this case supposed, and is extremely probable, that some peculiar species of matter is produced, capable of producing fever, on being applied to the body.”

2. Effluvia from putrid animal or vegetable matters. Of this our author seems to be less fully ascertained than of the former, as he does not say that he has observed any instances of fevers arising from this cause; and he concludes by observing that “either the cause of fever, consisting of matter produced in the body of a person affected with this disease, seems probably different from that produced by putrefaction, or might be generated without any putrefaction taking place.”

3. Cold. Our author “is not disposed to allow that sudden exposure to cold occasions fever to take place, unless some symptom of the disease follows immediately. If a man had been suddenly exposed to cold, and continued in perfect health for twenty-four hours, the author would never allow that fever, or any other disease, was occasioned by it. In this case (exposure to cold) the evidence is much stronger than in that of infection; for the author (Dr. Fordyce) has seen many instances where, from exposure to cold, the commencement of the attack was instantaneous; and many are to be found in the records of medicine.”

4. Moisture. On this subject the Doctor observes, that the application of water to the body is not a cause of fever, unless the air has particles of water floating in it; in which case fever has ensued more frequently than in other cases. Water may exist in the atmosphere in three states. 1. In small drops suspended in it like dust in water. 2. In vapour. In this case the transparency of the air is not impaired, and a chemical combination, as it is called, between the air and water takes place. If the atmosphere be hot or dense, it is capable of combining chemically with a larger proportion of water. If therefore the atmosphere should in this manner be saturated with water, at any particular degree of heat or density, by diminishing either of these the vapour will be condensed, and the water reduced to the former state of suspension in small particles. 3. Water, heated to the boiling point, emits a steam, which combines chemically with the atmosphere, till the latter be saturated, after which it assumes the form of small particles; and this last is the only state which has been found to produce fever.

Moisture will also produce fever when applied to the body by wearing wet clothes. Those which imbibe or part with heat most slowly, are least apt to produce fevers on being heated. The warmer the atmosphere, the more liable people are to fevers from moisture.

It has been observed, that moisture from marshes, stagnating canals, or where the water runs very slowly, is more apt to produce fevers than what proceeds from the sea, lakes or rapid rivers. “This (says the Doctor) has given occasion to suppose that some other vapours proceed from such marshes beside water, and produce the disease. It certainly often happens, that a considerable degree of putrefaction takes place in marshy grounds, and more especially in warm climates; but it is by no means to be concluded that moisture in the atmosphere always produces fever in consequence of putrefaction. Putrefaction can only take place in vegetable or animal substances. If water therefore, not impregnated with either, should be in such a situation as to produce moisture in the atmosphere, no putrefaction can take place; therefore, if fevers ensue, they are certainly in consequence of moisture, not putrefaction. Many instances of this may be brought, as in the war which took place in Flanders, between the tenth and eleventh year of the present century, an army encamped upon sandy ground, in which water was found in digging less than a foot deep, and occasioned a great moisture in the air, which produced in a few days numbers of fevers, although the army was perfectly healthy before, and no more fevers were produced on shifting their ground. There are a vast many other instances of the same thing having taken place. Besides, fever has often arisen immediately in persons sitting in rooms, the floors of which had been just moistened with pure water.”

5. Certain kinds of food. On this Dr. Fordyce observes, that, though food of difficult digestion undoubtedly produces a number of diseases, he has never seen it productive of fever excepting once. Dr. Girtanner relates, that the emperor of Germany, having forced a number of his subjects to serve as soldiers, and sent them into an unwholsome part of Walachia, where he fed them with a kind of paste made of bread and water instead of meat, many of them died of the scurvy. The Doctor, however, does not ascribe this to any positive cause, but to three negatives, viz. the abstraction of the stimulus of nutriment, by feeding on the paste just mentioned; of the stimulus of oxygen in the corrupted atmosphere of Walachia; and lastly of the nervous stimulus, the most powerful of all; the greatest part being engaged by force against their will. This corroborates what Dr. Fordyce has said, that bad food is very seldom the cause of fever; for among so many, who used the imperial paste just mentioned, some would certainly have been affected by fevers, had it been capable of producing them; but, as it did not, it is most evident that the deficiency of stimuli is not the cause of fever.

6. Passions of the mind. These are looked upon by Dr. Fordyce to be among the less frequent causes of fever, though it is certain that they have been productive of multitudes of diseases, and even of sudden deaths; and Dr. Falconer, in his Prize Dissertation, ascribes to the passions very considerable effects in fevers, and even in the plague itself. “Contagious fevers (says he) afford strong instances of the influence of mental affections, both as prophylactics and remedies. The plague is a remarkable example, and the same reasoning extends to other disorders of a febrile, contagious nature. Fear, it is well observed by Dr. Cullen, by weakening the body, and thereby increasing its irritability, is one of the causes which, concurring with contagion, render it more certainly active, which he ascribes to its weakening effect on the body, by which its irritability is increased. Against this therefore he directs the mind to be particularly fortified, which is best done by giving people a favourable idea of the power of preservative means, and by destroying the opinion of the incurable nature of the disorder, by occupying the mind with business or labour, and by avoiding all objects of fear, as funerals, passing-bells, and any notice of the death of particular friends. Even charms might be used with good effect, could we promote a strong prepossession of their efficacy, either by the confidence they inspire, or by their engrossing the attention of the mind. It is no less certain, that a studious regard to promote hope and confidence in recovery, is equally necessary for the cure as for the prevention of such disorders. We know that contagious fevers have a peculiar tendency to diminish the energy of the brain, and of course to debilitate the whole system; and that this is especially the case with the plague, which produces the most considerable effects in weakening the nervous[82] system or moving powers, and in disposing the fluids to a general putrescency; and Dr. Cullen is of opinion that to these circumstances, as the proximate causes of the plague, regard should chiefly be had, both for the prevention and cure of this disorder. It must therefore be highly necessary, during the course of this disease, to attend to the support of the spirits, as on these the vital principles greatly depend; and they can by no means be so effectually kept up as by inspiring a confidence of recovery.”

Dr. Zimmerman presents us with a great number of examples of the influence of the passions in producing diseases, or death itself; some of the most remarkable of which follow. “All the passions (says he) when carried to excess, bring on very formidable diseases. Sometimes they occasion death, or bring us at least into imminent danger. The most reputable physicians agree in opinion that terror may occasion apoplexy, and death; and indeed they consider apoplexy as the most common effect of violent passion. Without being carried to excess, a passion will sometimes occasion a difficulty of breathing, together with a sense of stricture in the breast, and an hesitation to speak; the tongue remaining as it were immoveably fixed on the palate. Hysterical and hypocondriacal affections are sometimes the effects of grief in the most healthy people. Joy is much more dangerous to life than sudden grief. Sophocles died through joy at being crowned on account of a tragedy he had composed in his old age. The famous Fouquet died on being told that Louis XIV had restored him to liberty. The niece of the celebrated Leibnitz, not suspecting that a philosopher would hoard up treasure, died suddenly on finding under her uncle’s bed a box containing sixty thousand ducats. Violent anger has sometimes produced hæmorrhages and subcutaneous extravasations; or, some vessel of the brain being ruptured by these transports, a fatal apoplexy has taken place. There have been instances of excessive anger being succeeded by epilepsy, colic, or a violent degree of fever. Sometimes it has occasioned an increased flow of bile. In some this produces vomiting; in others it goes off downwards, and causes diarrhœa; or being retained, from a stricture of the gall-ducts, will perhaps be absorbed, and occasion jaundice. In cases where anger has been succeeded by extreme grief, obstructions have taken place in the liver. The effects of terror are similar to those of anger, but in general more violent. Sometimes excessive terror seems to give to men a preternatural strength, as is the case with madmen and drowning persons. In some cases it has not only excited immediate convulsions, but caused them to return periodically. Fear has been said to make the hair stand upright, and to contract the pores from which the hairs issue in the same manner as cold does. There are instances in authors even of the colour of the hair being changed by excessive fright. Philip V died suddenly on being told that the Spaniards had been defeated, and, on opening him, his heart was found ruptured. Timid people are more liable than others to fall sick. A firmness of mind is one of the best preservations against contagion. Willis has very well observed, that they who fear the small-pox the most are generally the first to be attacked with it. Cheyne assures us that fear is extremely prejudicial in all epidemical diseases. Dr. Rogers remarks, that fear constantly increases the ravages of a contagious disease. Rivinus attributed the propagation of the plague at Leipsic wholly to fear. The French physicians, who wrote on the plague at Marseilles, went so far as to deny its being contagious, and ascribed its propagation chiefly to fear.”

As for the cause of the plague itself, Dr. Fordyce supposes it to be produced by an infection of a particular kind. That which takes place in Syria and Egypt, he says, has only been clearly described by Dr. Russel; and it cannot be gathered from the accounts whether this may be originally produced without having been propagated as the first class of infections above mentioned are. “That disease (says he) called the plague, which ravaged this country (England) on considering the histories of the disease, seems to have been a fever,[83] produced by infections of the first class which have been enumerated.” Dr. Moore has given an account of the origin of a plague, which, if it could be depended upon, would decide the question concerning the origin of this dreadful distemper without previous infection. This passage is extracted from the History of the Royal Medical Society for the years 1777 and 1778. “Dr. Mitchell, physician to the hospital at Smyrna, appears, according to a memoir of which he is the author, sent by M. le Baron de Tott to the Medical Society to believe in the spontaneity of the plague (or that it arises of itself without any predisposing cause in the body) for proof of which he cites the following circumstance: A solitary shepherd, having no communication with any body, fell sick while he was tending his flocks; he went into an inhabited part, where he communicated the plague with which he found that he was attacked. This circumstance would prove much, if it was certain that the shepherd had no communication with others; if it were known how long, and with what precaution, he had been secluded from company: but the proofs of these are too difficult to be established to allow of any conclusion to be drawn from the fact. We are obliged therefore to acknowledge [it to be a doubtful matter] whether it is in fact a country that is the cradle of the plague; what country this is, supposing that such an one exists; or, finally, whether it sometimes appears spontaneously, and whether the first whom it attacks becomes the focus from whence it emanates.”

Dr. Fordyce, in treating of the origin of fever, seems inclined to think that it may arise without any predisposing cause; and after having enumerated the various causes already mentioned, and fully considered them, gives it as his opinion, that “there must undoubtedly be other causes than those which give occasion to the disease, but which are at present totally unknown.” In like manner Dr. Moore, speaking of the nervous fever, sums up what may be known concerning the cause of it in the following words. “Upon the whole, we know that people of delicate, exhausted and sickly constitutions, and those whose minds are saddened by depressing passions, are greatly predisposed to this disease, the immediate seeds of which, we also know, may be generated in places where human effluvia are collected and confined. And this is the most essential part of our knowledge respecting the cause of this disease; and even this little is disturbed with uncertainty: for we sometimes meet with instances of people of robust constitutions, who are seized with the disease in all its malignity, when they are under no depressing passion, when the disease is not epidemic, to whom we cannot trace it from any place where the human effluvia could be confined in any uncommon degree, or from any person in the disease, of which perhaps there is no other person ill in the neighbourhood for several miles round; and, in short, when we cannot connect it with any of the causes supposed to be the sources of the distemper. On extraordinary occasions of this kind we have nothing for it but to suppose that, notwithstanding the apparent vigour of the patient, his body has been peculiarly predisposed to catch the infection, and that some contagion, not forcible enough to infect any other person, has by some means, unobserved, been conveyed to him; or, if so many suppositions displease, we may suppose at once that there is in some cases a source of this fever which has not been suspected. For, although the numerous observations that have been made give us the strongest reason to think that human effluvia produce this disease, we have no right to infer that it cannot arise also from some other source.”

To the same purpose I subjoin the very respectable opinion and testimony of Dr. Patrick Russel. “In some epidemical distempers, the sudden alternations of the air have constant and manifest influence; in others, though the influence of the air must be equally admitted, it seems not to depend on sensible alteration or succession in the common properties of the atmosphere, but on some inexplicable combination, some occult, new, unknown quality. Amongst epidemics of this last kind must be reckoned the plague. . . . Should ever that state of the air, without the concurrence of which the contagion of the pestilence never spreads, or ceases to act, be discovered, and ascertained by unequivocal marks, the dread of the plague, universally prevalent, would be greatly diminished; more effectual means of preservation would be found out, and the application of them might safely be limited to certain seasons.

“Experience in Turky, where, generally, no precautions are taken in the times of pestilence, clearly evinces, that, in a certain state of the air, a communication with infected places may subsist without any material consequence. The return of the plague at Aleppo happens at irregular periods; the intervals are of considerable, but unequal, length; and in those the commerce with Egypt, Constantinople and Smyrna remains uninterrupted. In the intervals between 1744 1760, and from 1762 to 1780, the plague raged several times in the places now mentioned, without affecting Aleppo; and even in two or three years subsequent to 1762, though it was at Marash, as well as other places not far distant, with which Aleppo has continual intercourse, no instances were discovered of communicated infection: if such happened, they must have escaped my utmost vigilance; and the daily exercise of my profession led me to be very much among the natives of all ranks. At the same time I have reason to suspect that infected families from some of those places took refuge in Aleppo; and I know, with certainty, that not only some merchants of that city, who happened to be at Marash when the plague broke out there, returned to their families in the summer of 1763, but that caravans of various merchandise arrived in the course of the same summer.

“I consider it therefore as an established fact in the Levant, that commerce and intercourse with infected towns is sometimes attended with no bad consequence. The same thing may perhaps be asserted, without restriction, of all countries; but till the signs indicating a pestilential constitution be ascertained, no particular year can be declared exempt from danger. Predictions founded on planetary conjunctions have been long exploded; and signs derived from the known properties and alterations of the air, are almost equally fallacious. The seasons concomitant with plagues in England, as well as elsewhere, have been very dissimilar; and the same visible concurrence, usually deemed pestilential, has often, in the revolution of years, been observed to return, in various countries, without producing the dreaded consequences. Upon the whole, from all I have been able to collect, the pestilential constitution seems hitherto to be known only from its effects; neither its approach nor its retreat can be predicted and its nature remains wrapped up in MYSTERIOUS DARKNESS.”

Having thus seen, that, of the causes commonly assigned for epidemical diseases, not one can be accounted certain and determinate, it now remains to consider one more, and that is

Contagion. Though this has been generally accounted the same with infection, yet by some it has been reckoned otherwise; and indeed there seems to be a necessity for such a distinction; for, though we should prove, ever so clearly, that a disease once communicated to one person should from that person be communicated to another, yet the difficulty is to know from whence the first person had it. This source, if any such can be found, is what we may with the greatest propriety distinguish by the name of contagion, and is the sense in which it shall for the future be used in this treatise, the matter communicated from one person to another being always called infection. This indeed differs from what many celebrated physicians have said upon the subject; but the distinction certainly must exist. Dr. Cullen speaks rather indistinctly upon the subject. “We have supposed that miasmata are the cause of intermittents, and contagions the cause of continued fevers, strictly so named; but we cannot with propriety employ these general terms. The notion of contagion properly implies a matter arising from the body under disease, miasma, a matter arising from other substances. But, as the cause of continued fevers may arise from other substances than the human body, and may in such cases be called a miasma, and, as other miasmata also may produce contagious disorders, it will be proper to distinguish the cause of fevers by using the terms marsh, or human effluvia, rather than the general ones miasma, or contagion.”

From this it is not very easy to determine what the Doctor means when he speaks of specific contagion as the cause of the plague. Dr. Russel plainly ascribes it to human effluvia. “The plague (says he) is a contagious disease; that is, an emanation from a body diseased, passing into one which is sound, produces, in time, the same disease,” &c. There must, however, undoubtedly have been something originally distinct from the human body which gave rise at least to the first plague that was in the world; and some plagues recorded in history are said to have arisen in this way. Thus, Ammianus Marcellinus says that the plague which broke out in the Roman army in the time of Marcus Aurelius arose from a pestilential vapour confined in a golden coffer dedicated to Apollo. Upon opening this, the contagion diffused itself all around, and the infection spreading from one to another, produced an almost universal pestilence. Ammianus indeed is the only historian who relates this; another account of its origin is given, p. 14, but whether we believe the account of Ammianus or not (which indeed does not appear probable) it is sufficient to show what were the received opinions at the time. In like manner every one has heard of pestilential effluvia breaking out from the earth, from graves, &c. so that we certainly look upon this doctrine of contagion as the cause of diseases to have been pretty generally received. We are also informed by Dr. Mead, from M. Villani, who wrote the history of those times, that the great plague of 1346 began in China, where, according to the report of some Genoese sailors, it was occasioned by a great ball of fire that either burst out of the earth, or fell down from heaven. This is thought incredible by Dr. Mead, and no doubt is so, but it shows the general opinion, that the original cause or contagion which produces a plague is distinct from the infection which is afterwards communicated from one to another. In the French Encyclopedie, we have this account of the ball of fire, or fiery vapour, without any comment.

As to the opinion of pestilential vapours arising out of the earth, though we are assured that people have been suddenly killed by explosions, probably of the electrical kind, or by lightning issuing from under their feet, yet we are not furnished with any well authenticated accounts of a plague having arisen from any such cause. About 19 years ago a violent fever raged epidemically through a small district in the north of Scotland, which was said to have originated in the following manner. Some young men having heard that a certain place in their neighbourhood had, in the time of a plague been a burial ground, took into their heads to dig into it. They did so, and one of them immediately fell sick, but recovered. The father of two of the young men, exceedingly displeased at the conduct of his sons, and apprehensive of the consequences, filled up the hole they had dug in the ground, soon after which he fell sick and died, and the fever continued to rage in the neighbourhood for some time. The mother of another of the parties concerned also died, and boils broke out on various parts of the bodies of the sick. This was the account given in some of the news-papers of the time, and had the matter been thoroughly investigated and attested, would have been decisive in favour of pestilential contagion being capable of taking up its residence in the earth. As it stands at present, it can only draw our attention to what may happen in another case, should any similar one occur.[84]

With regard to epidemics occasioned by the action of electricity, we cannot indeed produce any instance; but we have one of a distemper more dreadful than even the plague itself; and that is of a person suddenly struck by an electric flash (generated either in his own body, or in the room where he was) and by this stroke reduced to a most deplorable condition, which soon ended in death. The account stands on the authority of Mr. Joseph Battaglia, surgeon at Ponte Bosio, who transmitted it to Florence, and is as follows.

“Don G. Maria Bertholi, a priest residing at mount Valere in the district of Livizzano, went to the fair of Filetto, on account of some business which he had to transact, and after spending the whole day in going about through the neighbouring country, in order to execute commissions, in the evening he walked towards Fenille, and stopped at the house of one of his brothers-in-law, who resided there. No sooner had he arrived, than he desired to be conducted to his apartment, where he put a handkerchief between his shoulders and his shirt, and, when every body retired, he began to repeat his breviary. A few minutes after, a loud noise was heard in Mr. Bertholi’s chamber; and his cries having alarmed the family, they hastened to the spot, where they found him extended on the floor, and surrounded by a faint flame, which retired to a greater distance in proportion as it was approached, and at length disappeared entirely. Having conveyed him to bed, such assistance as seemed necessary was given him. Next morning I was called, and after examining the patient carefully, I found that the teguments of the right arm were almost entirely detached from the flesh, and hanging loose, as well as the skin of the lower part of it. In the space contained between the shoulders and the thigh, the teguments were as much injured as those of the right arm. The first thing, therefore, to be done, was to take away those pieces of skin; and, perceiving that a mortification was begun in that part of the right hand which had received the greatest hurt, I scarified it without loss of time; but notwithstanding this precaution, I found it next day, as I had suspected the preceding evening, entirely sphacelous. On my third visit, all the other wounded parts appeared to be in the same condition. The patient complained of an ardent thirst, and was agitated with dreadful convulsions. He voided by stool bilious putrid matter, and was distressed by a continual vomiting, accompanied with a violent fever and delirium. At length the fourth day after a comatose sleep of two hours, he expired. During my last visit, while he was sunk in the lethargic sleep of which I have spoken, I observed with astonishment, that putrefaction had already made so great progress, that his body exhaled an insupportable smell. I saw the worms which issued from it crawling on the bed, and the nails of his fingers drop of themselves; so that I thought it needless to attempt any thing farther, while he was in this deplorable condition. Having taken care to get every possible information from the patient himself, respecting what had happened to him, he told me, that he had felt a stroke, as if somebody had given him a blow over the right arm, with a large club, and that at the same time, he had seen a spark of fire attach itself to his shirt, which in a moment was reduced to ashes, though the fire did not in the least injure the wrist-bands. The handkerchief which he had placed upon his shoulders, between his shirt and his skin, was perfectly entire, without the least appearance of burning, his drawers were untouched, but his night-cap was destroyed, though a single hair of his head was not hurt. That this flame under the form of elementary fire, burnt the skin, reduced the shirt to ashes, and entirely consumed the night-cap, without in the least touching the hair, is a fact which I affirm to be true: besides, every symptom that appeared on the body of the deceased, announced severe burning. The night was calm, and the circumambient air very pure: no bituminous smell could be perceived in the chamber, nor was there the least trace of fire or of smoke. A lamp, however, which had been full of oil, was found dry, and the wick almost in ashes. We cannot reasonably suppose this fatal accident to have been occasioned by any external cause; and I have no doubt that if Maffei were still alive he would take advantage of it to support an opinion which he entertained, that lightning is sometimes kindled in the human body and destroys it.”

Another account, to the same purpose, is given in Mr. Battaglia’s paper. “On the 21st of April, 1781, the first battalion of the brigade of Savoy set out from Tortona, in order to go to Arti, when the weather was excessively hot. On the 22d, having made rather a forced march, the soldiers suffered a great deal from the ardour of the sun, so that, at the village of Serre, where they halted, one of them, named Bocquet, a man of twenty-five years of age, whose skin being very hard and thick had not perspired, sent forth a loud cry, which seemed to announce some extraordinary commotion, and instantly fell down. Mr. Bianet, surgeon major to the regiment, found the patient in convulsions. When he was carried to the hospital the upper part of his body, to the thighs, appeared to be withered and black, and in a gangrenous state. Mr. Bianet employed scarifications, but without effect; it was impossible to make him swallow any thing; and it was found necessary to abandon him to his dismal fate. His body soon exhaled a putrid smell, and he died at the end of five hours. That his disorder might not be communicated to others, he was interred together with his clothes. Upon inquiry, after his death, it was found that this man was addicted to the constant use of spiritous liquors, and that he had even drank of them to excess upon the march.”

Other instances there are, still more terrible, of people actually taking fire and being consumed to ashes by some internal cause; but, as nobody was present either at the beginning or during the continuance of these extraordinary inflammations, nothing certain can be said about them. That such things, however, have happened, is certain, of which one of the most remarkable instances is that of Signora Corn. Zangari, an Italian lady. She retired to her chamber in the evening somewhat indisposed, and in the morning was found in the middle of the room reduced to ashes, all except her face, legs, skull and three fingers. The stockings and shoes she had on were not burnt in the least. The ashes were light, and on pressing them between the fingers vanished, leaving behind a gross, stinking moisture, with which the floor was smeared; the walls and furniture of the room being covered with a moist cineritious soot, which had not only stained the linen in the chests, but had penetrated into the closet, as well as into the room overhead, the walls of which were moistened with the same viscous humour. This lady had been accustomed to use a bath of camphorated spirit of wine when indisposed.

Dr. Zimmerman, from the 64th volume of the Philosophical Transactions, relates the case of a poor woman who perished in this miserable manner at Coventry in England in the year 1772. “She fell out of bed, and was found next morning burnt to death, though the fire in the grate had been small, and the furniture in the room had suffered but little. Except one thigh and leg, there were not the least remains of any skin, vessels or viscera; and the greater part of the bones were completely calcined, and covered with a whitish efflorescence.”

On these unfortunate people it has been observed that they were generally intemperate in the use of spiritous liquors. Of the poor woman at Coventry, whose case has been just now related, it is said, that she had been in the practice of drinking from half a pint to a quart of rum every day, and this she continued, notwithstanding her being affected with jaundice and other complaints. Mr. Wilmer, who communicated this case to the Royal Society, concludes it with these words: “That her solids and fluids were rendered inflammable by the immense quantity of spiritous liquors she had drank, and when she was set fire to she was probably soon reduced to ashes.”

On other cases of a similar nature it has been remarked, that the miserable sufferers were “for the most part advanced in years, remarkably fat, and had been much addicted to the use of spiritous liquors, either in their drink, or applied in friction to the body; whence it has been concluded that these people perished by their whole substance spontaneously taking fire, the principal seat of which had been the entrails, or the epigastric viscera; and that the exciting cause was naturally found in the phlogiston of the humours, called forth by that of the spiritous liquors combined with them.”[85] But solutions of this kind cannot by any means be admitted. We have not the smallest reason to think that either the solid or fluid parts of the bodies of hard drinkers are more inflammable than those of other people; neither is it credible that any person could live with his body in such a state. Besides, the most inflammable bodies will not begin to burn unless fire actually be applied to them, while others much less inflammable to appearance, will yet take fire spontaneously. Thus, even spiritous liquors themselves, though they flame violently when thrown into a fire, or when a burning body is applied to them, yet there is not an instance of such liquors taking fire of themselves; nay, they cannot even be set on fire by pouring them upon a red-hot iron, while, on the other hand, heaps of wet vegetables, which we should think scarce at all inflammable, do yet very frequently take fire spontaneously. The author lately quoted, however, justly observes that M. Bartholi, the unfortunate priest above mentioned was plainly struck first by electricity from without, a spark of fire attaching itself to his shirt, and a faint flame surrounding his body; so that the fire did not seem to have been generated in his body, but in the atmosphere. There are instances of people being surrounded with these luminous appearances without being hurt; particularly of a woman at Milan, whose bed was surrounded with a light of this kind. Mr. Loammi Baldwin, of this country, was also surrounded by an electric light, while raising a kite in the time of a thunder storm, and Dr. Priestley makes mention of a gentleman, who, after having worked an electric machine for a long time in a small room, perceived, on leaving it, a luminous vapour following him. But the instances most to our present purpose are some recorded in the Philosophical Transactions, of luminous vapours coming from the sea, attaching themselves to corn-stacks, and setting fire to them. One of this kind is particularly mentioned in Lowthorp’s Abridgement of the Transactions, as having taken place in Ireland, coming repeatedly from the sea, and setting fire to corn and hay, so that the people were greatly alarmed. At last they found that it might be driven off by making a great noise, and that it would avoid any sharp-pointed iron instrument. Had such a vapour attached itself to a human body, it is possible that it might have set fire to it as well as to the stack of corn or hay. Whether these accounts render the story of the Genoese sailors concerning the ball of fire occasioning the plague of 1346 more credible, we leave the reader to judge. They certainly show, however, that the electric fluid will sometimes interfere with the human body in a very terrible manner, producing, where it does not kill instantaneously, symptoms equal to those of the very worst plague, as in the case of the priest and soldier above mentioned.

Another hypothesis concerning the origin of pestilential diseases is that of swarms of little animals invisibly existing in the atmosphere; which, being taken into the body by the breath, are supposed to corrupt or otherwise vitiate the blood and other parts of the body, as we see in the plague and other epidemic disorders. This hypothesis, so generally exploded, and so apparently improbable, seems to receive some support from a discovery of an insect made by Mr. Henry Baker, F. R. S. and published in his work entitled “The Microscope made Easy.” He called it the insect with net-like arms. “It lives (says he) only in cascades, where the water runs very swift. Some of them being kept in a vial of water, most died in two days, and the rest, having spun themselves transparent cases, which were fastened either to the sides of the glass, or to pieces of grass put into it, seemed to be changed into a kind of chrysalis; but before they assumed this form, they altered their shape (in a manner he represents by a figure.) None of them lived above three days; and, though fresh water was given them two or three times a day, yet in a few hours it would stink to a degree scarce conceivable, and that too at several yards distance, though, in proportion to the water, all the included insects were not more than as one to one million, an hundred and fifty thousand. This makes it probable that it is necessary for them to live in a rapid stream, lest they should be poisoned by the effluvia issuing from their own bodies, as no doubt they were in the vial.”

From this account it is not difficult to conceive that animals, though exceedingly small, may yet emit such poisonous effluvia as will destroy much larger ones in their neighbourhood. It will by no means be incredible that, had one or two such offensive animals been thrown into a jar containing gold-fishes,[86] the whole of these beautiful inhabitants would have perished at once. Let us suppose such a thing to have actually happened; that a malicious person had put them in over night, and in the morning the proprietor of the fishes finds them all dead, and the water offensive to the last degree. He sends for a neighbouring philosopher, who, happening to be ignorant of the existence of such animals, endeavours to account for the phenomenon upon some of the received principles of philosophy. How much theory would here be wasted, and what endless disputes might ensue without even a possibility of arriving at the truth! Just so it is with epidemic diseases. The cause is invisible, and, until it becomes discoverable by our senses, it can never be known; for, as has already been observed, a cause never can be known merely by its effects, unless we have seen it, or somebody who has seen it gives us information. And this will certainly be found to hold good in every instance, even from the Supreme Cause himself to the diminutive insect just mentioned.

Lastly, I shall consider another possible source of epidemics, which has been hinted at by others. Allowing that infectious matter proceeds from the body of a diseased person, as much must issue from a single patient as is sufficient to bring the disease upon thousands, and with regard to the small-pox and some other distempers we certainly know that it is so. This infection is dissipated in the atmosphere, and intimately combined with it, so that it becomes imperceptible and harmless; but we have no reason to suppose that it is annihilated, or cannot be re-produced in its pristine state. Water, though perfectly dissolved, and to appearance deprived of existence in the air, may yet be precipitated from it, and pour down upon us in deluges. What happens in one case may happen in another. The infectious matter, dissolved in the air, may by some natural cause be precipitated from it, overshadowing whole regions, and, if it be not powerful enough to produce the epidemic of itself, may certainly predispose to it in such a degree, that the slightest additional cause will bring it on.

Something indeed of this kind would seem really to be the case, otherwise we cannot well conceive why there should be such a distinction of diseases. Thus the infection of the small-pox is the same all over the world. The variolous matter will never produce the measles in any country, nor will the typhus produce a pleurisy. The plague manifests itself to be the same distemper in all its various degrees of malignity, though even this dreadful disease is sometimes so mild that it does not confine the patient to his bed. There must therefore be some certain constitution in the nature of the cause which produces such and such diseases, as certainly as in the seed of particular vegetables, which gives to each its proper appearance and shape. The cause of the disease so modified we may call, with Dr. Cullen, its specific contagion.

Having thus treated so largely upon contagion of different kinds, it now remains to consider the objections that have been made to the doctrine altogether. It is indeed surprising that in so great a length of time, after the world hath so often and so dreadfully suffered from the violence of plagues, the simple fact, whether it be infectious or not, should not have been determined: nay, that it should still be questioned by physicians of no mean reputation whether such a thing as contagion or infection can possibly exist. Dr. Mosely in his treatise on tropical diseases treats the whole doctrine of contagion with the utmost contempt; calling it “a field for speculation, which has long amused the pedantry of the schools, and should never be entered into by practical writers.” Notwithstanding this, however, he doth enter into it, and with such bad success, that in the very first paragraph he is obliged to derive the cause of diseases from the stars! “There are some diseases we know, (says he) which follow the changes of the atmosphere; but there are others which make their revolutions, and visit the earth, at uncertain periods; for which we can trace no cause, depending on combinations, in which, perhaps, the influence of the planets may have some share.” Here we have a still wider field for speculation than even the schools have given us; for the Doctor ought to remember that the influence of a planet, producing a disease, is as truly contagion as the effluvia of a dunghill; and if we have a wide field to traverse when tracing it through the earth, we have one infinitely more extensive in pursuing it through the heavens. But we may be assured that planetary influence does not produce diseases; for, if it did, they would in all times of pestilence overspread the face of the earth, as the influence of the planets, if they have any, certainly does.

The arguments used by this author against terrestrial contagion are,

1. “It has often happened that hundreds of men in a camp have been seized with the dysentery, almost at the same time, after one shower of rain, &c. People under similar circumstances must be subject to similar diseases: and yet it often happens that dysentery begins with a few people, and spreads itself by degrees until a multitude are affected.”

This argument rather militates against himself; for, if dysentery or any other disease was occasioned by an evident general cause operating upon persons in similar circumstances, all of them ought to be taken ill at once; but Dr. Mosely owns that they frequently are not. There must, of consequence, be something less evident which determines the disease to particular persons, while the general cause operates equally upon all. This less evident cause we call contagion.

2. “It is incredible that the smelling a little human blood, that had stood some months in a phial, gave the man a dysentery mentioned by Pringle; or that the person Forestus speaks of got the plague by only putting his hand into an old trunk; or that the shaking an old feather-bed, which had lain by seven years, raised a plague at Wratislau, which destroyed five thousand persons in twelve weeks, as related by Alexander Benedictus, &c.—Such things may be true, but, when probability is shaken, reason always inclines to skepticism.”

Here our author most evidently contradicts himself; for in the beginning of the paragraph he tells us that the things related are incredible, and in the end of it, that they may be true. The argument, if it may be so called, is mere assertion. It is incredible that the smell of putrid human blood in a vial should produce the dysentery. Why should this be more incredible than that smelling to a charged vial should ensure an electric shock to the person who did so? This is entirely a question respecting a matter of fact, not of speculation. The same is the case with the rest. It is not more incredible that, if the infection of the plague was in a trunk, a man should get the plague by putting his hand in it, than that he should be burnt if he put his hand into a trunk full of hot ashes. Before the Doctor decided in such a positive manner, he ought to have proved that no infection could be contained in a trunk; but this, though the very point in question, he takes for granted, first telling us that the contrary is incredible, and then that it may be true!

3. “We observe in camps and hospitals, that those people whose dirty employments subject them in a particular manner to a depravation of their habits, seldom escape the present epidemic; and this gives rise to the vulgar expression, and very incorrect notion, of catching the disease. And we observe that others from the slightest deviation from regularity lose the power by which the body resists diseases, and they are also attacked. But these attacks are not to be attributed to infection: for those people who keep the vital and animal powers in uniform confederacy, by temperance and calmness of mind (for fear, by lowering the vital energy, subjects the body to disease) nourishing diet, proper clothing and cleanliness, and keeping a free and regular passage for all excretions, are proof against the assaults of foul and pestilential air. Such people seldom suffer even by the plague itself: while all around them perish.”

The first sentence of the above paragraph is so obscurely worded, that it is difficult to know the author’s meaning. I know not of any lawful employment so dirty that it necessarily subjects the person who practises it to a depravation of habit. The next ascribes every thing to intemperance and fear; from which, it seems, we are to infer that none but drunkards, cowards, and dirty, naked ragamuffins, are ever seized with epidemic diseases. But of this we are able to bring a direct disproof. I suppose Dr. Mosely will not say that the celebrated Prince Eugene of Savoy was either a coward or a drunkard; that he had a dirty employment, wanted proper food or clothes, or was deficient in personal cleanliness; yet, when in the marshy parts of Hungary, he was in danger of death from an epidemic dysentery, notwithstanding that he was so careful in respect of diet, that he had pure water brought him every day, probably from a considerable distance. How came he to be affected by the distemper under such circumstances, while Count Boneval, though as an inferior officer he probably enjoyed fewer advantages, remained free from it, taking only a small quantity of Peruvian bark daily? It is uncertain whether the bark did really preserve him or not; but the case of Prince Eugene plainly shows that sobriety, temperance, valour and cleanliness are not sufficient to ward off an epidemic disease, if people come in the way of infection.

4. “It should follow, if contagion were supported by infected bodies, that no person should ever escape infection (as at Oxford assizes in 1577[87]) who was within the sphere of its action; and that those who were entirely secluded from it, and free from all contiguity to infected people, or substances, as the collegers were in the town of Cambridge, when the plague was last in England, should be exempt from it.

“But, in opposition to this, Rhazes lived 120 years, an often practised in plagues. Hodges remained in town, and attended the sick, during the great plague in 1665. Kaye was in the midst of practice in the sweating sickness in 1551, without any inconveniency. Procopius informs us, that during a terrible plague at Constantinople, in 543, which almost destroyed the whole city, no physician nor other person got the plague by attending, dressing or touching the sick. Yet most of the Capuchins, the Jesuits, the Recollets, the Observantines, the Barefooted Carmelites, the Reformed Augustines, all the Grand Carmelites, the Grand Trinitarians, the Reformed Trinitarians, the Monks of Loretto, of Mercy, the Dominicans, and Grand Augustines, who kept themselves secluded in their several convents, and took every precaution to avoid the plague, while it raged at Marseilles, perished by it.

“There are no epidemical nor contagious diseases that attack every person who breathes the same air, or that is in contact with the infection, else whole regions would be depopulated. The habit must be graduated, or adapted, for the reception of a disease. In some constitutions of body the access is easy, in some difficult, in others impossible. But where the revelation of this mystery is to be found, none can tell.”

In this, which our author seems to have designed as his grand argument, it is plain that the deficiency is as great as in any of the rest. If we suppose the plague, or any other epidemic disease, to arise from some general cause, let that cause be contagion or any thing else, it ought to operate upon all who come within its sphere of action, as Dr. Mosely observes of infection. If experience shows that it does not, the argument will hold equally against a constitution of the atmosphere, putrid effluvia, heat, cold, or any thing else; and in fact the Doctor fairly gives up the point at last, by resolving the whole into an unrevealed mystery. With regard to what he says about the plague at Marseilles getting into the convents, of which he presents us with such a catalogue, it is impossible to know what precautions were used, and we are assured that in Turky it is thought necessary for the Europeans not only to guard against a communication with their own species, but some of the brute creation also. Cats particularly are dreaded so much, that a general massacre of them commences among those who use precautions, the favourites of that species must be sent to a distance, and M. Volney mentions two merchants who had shut up their houses, and yet had the plague imported by a cat. In short, considering that infection is supposed to be altogether invisible and imperceptible, it is impossible to say how it may be conveyed, or to what extent it may occasionally act when once brought into a country. Dr. Fordyce is of opinion that the distance at which infection may act depends on the disposition of the air at the time; and he observes, that a difference in this respect is observable in the odoriferous effluvia of vegetables. “If the air be loaded with moisture, they reach to a much greater distance. Vapour arising from a field of beans, for instance, or a putrid ditch, is sensible to the nostrils at a greater distance if the air is moist.” He observes indeed that this has never been verified with regard to infection; but as it is evidently the case with putrid effluvia, which very often accompany infection, we may reasonably conclude that it is the case with the latter also.

Let us next take a view of what is advanced by the authors of The Science of Life upon this subject. Mr. McLean, who puts his name to this part, informs us of his conviction “that no general disease, which affects a person more than once during life, can ever be communicated by contagion;” and he defines contagion “a specific matter, generated in a person affected with disease, and capable of communicating that particular disease, with or without contact, to another.” It would here be no improper question, by what means he comes to know that a contagious disease can affect a person only once. But even this question is unnecessary. Dr. Guthrie gives an account of a gentleman who had the courage to inoculate himself for the plague, in consequence of which he had the disease with the concomitant symptoms of buboes, &c. Here then we see the plague communicated by “a specific matter generated in a person affected” with the same disease, i. e. by contagion, according to Mr. McLean’s own definition. The dispute therefore might stop, as this fact seems to be decisive on the subject; but as he has at great length insisted upon the argument last quoted from Dr. Mosely, it seems necessary to follow him a little farther.

“If a person (says our author) be affected with any disease, it will necessarily be communicated to every other person who comes within the infectious distance, and is not at the same time labouring under some disease higher in degree.” This proceeds upon a supposition that his theory is absolutely perfect and infallible; which, however plain it may appear to himself, will not probably be admitted by others without some proof. Indeed he himself afterwards adduces some facts which decisively overthrow it. “A child (says he) here and there is exempted from small-pox, even though exposed to its contagion.” How comes this to pass? The disease, we are told, is contagious, the child is exposed to the contagion, and yet is not affected. In all such cases it would be ridiculous to suppose the subjects labouring under a disease higher in degree than the contagion could produce. In numbers of instances of this kind the children were evidently in good health, and yet would perhaps be seized at an after period when no more exposed to contagion than they had been at first.

“Small-pox, measles, and other general diseases, which occur only once during life, never disappear, until the whole of those who have been within the infectious distance, and were not at the time labouring under some disease higher in degree, have received the infection. As these diseases are very mild, children sometimes resist the power of contagion from the superior force of some other diseases, although they may be so slight as to escape common observation.”

In this paragraph we have the favourite maxim of our author repeated, twice indeed, without a single fact to support it. Instead of this we find hypothesis heaped upon hypothesis, as the giants are said to have heaped mountains upon one another in order to get up to heaven. He first supposes that the infection of the small-pox seizes on the whole of those on whom it falls. The exceptions to this maxim he explains by another supposition, viz. that the contagion of the small-pox is counteracted by another disease. The second hypothesis is supported by a third, and that a very extraordinary one, that the small-pox (a disease which has destroyed innumerable multitudes) is very mild; and this third by a fourth, that the diseases which counteracted the contagion were so slight as to escape common observation. It was incumbent on Mr. McLean to have pointed out some of those diseases, and to have informed us how they came to counteract this contagion. But it is needless to argue with one who writes so extravagantly. Far from the mode of reasoning followed by Dr. Fordyce, who decided from the majority of facts, our author determines every thing by his own preconceived opinions. “That the power which occasioned disease at the Oxford assizes (says he) was not contagious matter, is proved by its producing diarrhœa in some, while it produced fevers in others.” But, if it was not contagious matter, what kind of matter was it? Or how comes our author to know that those who were affected by the diarrhœa were not likewise affected by fever? How many fevers are attended by diarrhœa, or how many cease when diarrhœa comes on! It would have been equally conclusive to say that the matter was not contagious, because some died and some recovered.

I shall only take notice of one assertion more, it being both tedious and unnecessary to follow him through the whole. “From every record of epidemic and pestilential diseases, it would appear, that they have their stated periods of recurrence; that these periods are such months as are most remarkable for vicissitudes of the atmosphere; that they become general only in those years in which these vicissitudes are extreme; that they do not occur in seasons when the heats or colds, however intense, are equable; nor in years when the state of the atmosphere is tempered throughout; and that they uniformly cease with the establishment of an equable state of the atmosphere, whether the weather be cold or hot. . . . In Aleppo, according to Dr. Russel, the Europeans regularly shut themselves up in their houses every year, at some period between April and July; and the rich natives begin to adopt the same plan, &c. . . . From this fact it appears, that the plague occurs at Aleppo, in a state more or less mild, almost annually, and that it commences and ceases at certain known periods. But it has been remarked that, in its most severe state, this disease recurs only at periods of ten years, or thereabouts: a regularity which cannot, upon any known principle, be attributed to a power of such casual application as contagious matter.”

In the beginning of this paragraph our author makes a bold appeal to every record of epidemic and pestilential disorders; but here we may ask, Has he consulted every record of these disorders? That he has not, we may readily believe; but even those which are hinted at seem either to have been very inaccurately consulted, or wilfully misrepresented. To evince this I subjoin the following abstract of what Dr. Alexander Russel says of the plague in general, with the annotations of his brother, Dr. Patrick, taken from Russel’s Natural History of Aleppo.

The inhabitants of Aleppo suppose that the plague visits them once in ten years, and that it is always imported; and the most severe plagues are thought by some to come from Damascus, while others contend that they come from the northward. Dr. Alexander Russel thinks this popular opinion of the return of the plague not altogether unfounded; and he thinks it also probable that it never invades Aleppo without having previously attacked either Damascus or Khillis, Aintab, Marash or Uufa. He thinks that its appearance always is in one of the maritime towns of Syria; if in Sidon, Byroot or Tripoli, Damascus is commonly the channel by which it reaches Aleppo; but, if it shows itself first at Scanderoon or Byass, its approach is by the way of Khillis or Aintab.

On this Dr. Patrick Russel observes, that the account of Aleppo being visited only once in ten or twelve years is confirmed by a letter from an English gentleman, in 1719, who had resided there for 30 years. The dates of the plagues which Dr. Patrick had procured were, 1719, 1729 and 1733. Another began in 1742, and terminated in 1744; from which time there was no return till 1757 or 1758, when it continued at Aleppo till 1762, and did not entirely quit the country till 1764. The plague of 1719 was said to come from the northward, but this appeared to want confirmation; but all accounts agree that it raged at Tripoli, Sidon, &c. two months before it appeared in Aleppo. Egypt was ravaged by the plague in 1728, as was also Byass and the neighbouring parts in the same summer; and next year it appeared at Aleppo. In 1732 it raged at Sidon, Tripoli and Damascus; next year it seized Aleppo.

Dr. Alexander goes on to inform us, that the disease never spreads much in winter. It advances with the spring, comes to its height in June, declines in July, and terminates in August. “None (he says) are ever seized with in September and October, not even in the plague of 1742, which returned three years successively;” but Dr. Patrick says that this was not confirmed by his experience in 1760, though he owns that the distemper declines remarkably at that period; and the natives are greatly inclined to have it believed that the distemper has totally ceased, and to deceive the Europeans in this respect. The times at which the Europeans shut up and come out of their confinement show only the increase or decrease of the disease, but not its beginning or ending. The plague of 1719 made terrible havoc. Europeans then shut up about the middle of March, and kept confined till the middle of July. In 1729 they did not shut up till the middle of May, and were not confined above a month, the number of sick being small. In 1733 they were confined from the middle of March to the middle of July, but the distemper was less violent than in 1719. In 1742 the time of confinement much as in 1729. In 1743 shut up April 11, and opened the middle of July. The plague violent, but less so than in 1733. In 1744 few shut up, the number of sick being inconsiderable. In 1760 they shut up on the 30th of June, and continued about a month. In 1761 shut up May 28, rode out Aug. 1, and opened completely the 10th of that month. In 1762 they were confined from the last week in May to the first of August. From 1762 to 1787, a larger period than usual, the city was free from the plague. In 1787 it broke out among the Jews in the month of April, increased in May, raged violently in June, and terminated in July.

From these accounts it appears, as Dr. Alexander Russel informs us, that the plague of one year differs remarkably from that of another; but he says, that, at Aleppo, it is never attended with such scenes of horror as have been known in European countries; for which Dr. Patrick assigns the following reasons: 1. The markets are constantly supplied with provisions. 2. The dread of the contagion is much less. 3. The sick are less liable to be deserted by their attendants (but this, according to his own observation, is not always the case) and 4. The regular, speedy interment of the dead prevents a spectacle far from uncommon in the European plagues, and which of all others is the most shocking to humanity.

“Extreme heat (says Dr. Alexander) seems to check the progress of the distemper. July is a hotter month than June, and the season wherein the plague ceases at Aleppo is that in which the heats are most excessive.” His experience did not confirm a popular opinion at Aleppo, and which has likewise been adopted by many medical writers, that the moon has any influence on the distemper. To have had the distemper once does not secure a person against future attacks. Numbers of people who were alive when he left Aleppo had it twice or oftener; and he had instances of some being infected thrice in one season. Dr. Patrick Russel has observations to the same purpose.

From this it appears, that the popular opinion at Aleppo, which Mr. McLean wishes to establish as a certainty, is by no means so well founded that we can build any theory upon it. The misfortune is, that, wherever a theory is built upon any thing said to be constant and invariable, a single failure overturns the whole. Now, in the dates of plagues above mentioned, the variations are so great that it is impossible to draw any certain conclusion from them. In the first three instances of 1719, 1729 and 1733 there is indeed a coincidence of the first two, but the last falls short by no less than six years. What then does Mr. McLean mean by his “ten years, or thereabouts?” Can thereabouts imply a difference of more than half? The English gentleman’s testimony who resided 30 years in that country could extend no further than to three plagues, and even these are not mentioned. The fourth instance in 1742 is deficient in one year; the fifth in 1757 or 1758 exceeds by three or four years, and the sixth from 1762 to 1787 by no less than fifteen years.

An anonymous writer in a Scots periodical publication entitled “The Bee,” has partly adopted the above opinion, but adds others for which he has not thought proper to adduce any authority. “It visits most parts of Asia once in ten or twelve years, and carries off an eighth or tenth of the inhabitants. There have been plagues which have carried off one fourth of the inhabitants. The farther east you go, the less frequent it is—every 20th, 40th, and, even at Bassorah, every 90th year; but then this scourge is most dreadful. The last plague at Bassorah, which had not visited the city for 96 years, carried of more than nine tenths of the inhabitants.”[88] It is astonishing that people will write in such a manner as to subject themselves to endless criticism on account of their inconsistency. The plague, this writer says, visits most parts of Asia once every ten or twelve years, and yet it goes no farther east than Bassorah; a space scarce equivalent to the twentieth part of Asia! Even in this small space, it varies from ten or twelve, to twenty, forty, or even ninety years; and, to complete the whole, instead of giving any instance of the periodical return of the plague at an interval of ninety years, we have one of its disappearance for ninety-six years!

From all this it is evident, that no dependence can be placed on such vague accounts with regard to the periodical returns of the plague. Even the time of shutting up the houses in Aleppo is not accurately related, for, from the above abstract it is plain, that they are sometimes shut up in March; while Mr. McLean would have us to believe that it is always between April and July. It is needless to wade through a jumble of unsupported assertions, which, being backed by no evidence, fall to the ground of themselves. “I will venture to assert (says he) that no person in perfect health ever was or can be exposed to the power of contagion, without receiving the specific disease which that contagion produces; excepting in small-pox, measles, &c. when the person has previously had the disease.”—How comes he to know all this? Or, though our author ventures to assert, must we of necessity venture to believe? When he ascribes the origin of epidemics, and the plague itself, to the vicissitudes of the atmosphere, not a single fact is adduced in support of his hypothesis. One very strange proof indeed he brings from Dr. Rush, viz. that the latter had been informed by a gentleman who resided in tropical countries, that, in the month of July, several weeks before the yellow fever became general, he had observed a peculiar and universal sallowness of complexion in the countenances of the people of Philadelphia, such as he had seen in those of the more southern countries before the appearance of bilious fevers in them. Surely it is a very strange mode of argument to tell us of the colour of people’s countenances instead of the states or vicissitudes of the atmosphere, which we are made to believe were the causes of that change. Another quotation is made from the same author in which a warm, dry, stagnating air is conjectured to have been the cause of diseases; but he does not even quote Dr. Rush saying that it was the cause of yellow fever, much less of all epidemic diseases. Besides, to say that any thing is occasioned by a state, or vicissitude of the atmosphere, is such a vague mode of expression, that it must either mean nothing, or be contradictory to itself. A state of the atmosphere we must suppose to mean that it continues for some time either to be wet or dry; a vicissitude, when it changes from one to the other. If an epidemic then is produced by a state, it cannot also be produced by a vicissitude, of the atmosphere: or, if some epidemics are produced by states, and others by vicissitudes, we ought to be informed which produce one kind, and which another. But throughout the whole of this dissertation we have neither distinctness nor regularity, nor indeed any thing but assertion, supported only by an imaginary theory.

Dismissing at length therefore these conjectural theories, let us endeavour to deduce from certain and undoubted facts the connexion between the state of the body, and the operations upon it of other causes, invisible indeed to our eyes, but discoverable by our rational faculties, and in some measure capable of being made the objects of our senses also.

1. From the account given of the structure of the human body, it undeniably follows, and has already been observed, that all parts of it are so connected together, that none can suffer any very grievous injury without affecting all the rest.

2. The life of man depends immediately on the air. From this element the blood receives heat and a vital spirit diffusing itself from the blood along the nerves, and thence expended in the operations of life and sensation.

3. From undoubted experiments[89] it appears, that this vital spirit possesses in a great degree the properties of electricity, insomuch that many suppose them to be the same. This is indeed denied by the celebrated anatomist, Dr. Monro, but he allows that the nervous fluid is similar to electricity, and it is certain that the electrical fluid can affect it in such a manner that we may reasonably believe them to be the same.

4. The air acts upon the blood by the latent heat it contains. The air itself is composed of something volatilised by heat. In some cases this is evidently a terrestrial substance, as in that of inflammable air, or hydrogen, which is formed of charcoal volatilised by heat, with the addition of a little water. In the case of oxygen, or dephlogisticated air, the combination seems to be the matter of heat (which I shall hereafter distinguish by the name of the ethereal fluid) with water deprived of its carbonic principle. This coincides with the opinion of Dr. Priestley, who says that the basis of dephlogisticated air seems to be dephlogisticated water. But, let the basis be what it will, the ethereal fluid which volatilises it is the agent; the basis is entirely passive, and only modifies or restrains the action of the other fluid, so that it does not exert itself except in particular cases. Fixed air, or carbonic acid, is composed of the base of oxygen united with a certain portion of carbon, and the whole volatilised by the ethereal fluid. Phlogisticated air, azote, or septon, according to Dr. Priestley, consists of the basis of dephlogisticated air along with a certain proportion of carbon different from that which produces fixed air, volatilised by the same agent;[90] and so we may determine concerning every other species of air.

5. In certain cases the ethereal fluid quits those substances with which it is united: the air is then decomposed, the substance into which the other fluid enters is heated, or rendered more fluid than before (perhaps both) while the basis either unites itself to the moisture of the lungs, or is thrown out by the breath. Whether in any case the basis can pervade the membranes, and thus mix itself with the blood, notwithstanding the positive assertions of Dr. Girtanner and others, is very doubtful, and does not admit of any positive proof.

6. The blood, being a fluid, must be subject to the same laws with other fluids. A certain quantity of latent heat must be contained in it, in order to give the degree of fluidity naturally belonging to it. If this quantity be augmented, the fluidity will be augmented, and the blood will become thinner; if it be diminished, the contrary will take place; and if we suppose a great proportion of this latent heat to be abstracted, it is not unreasonable to suppose that something like a congelation may take place, and the blood be changed into a solid substance of such a nature as cannot any more be made to resume its former qualities.

7. By augmenting the sensible heat, the blood is affected in the same manner as any other fluid; it suffers expansion, by which the vessels are dilated in proportion, and, if this expansion and dilation be carried to a certain length, a rupture of many of the small vessels, and apoplexy, or some other grievous disease, may ensue.

8. By breathing certain kinds of air, the fluidity, heat and expansion of the blood, and of consequence the dilation of the blood-vessels, are affected. Thus, when a person breathes a quantity of the fume of charcoal, containing much fixed air, he feels himself affected with pain and a sensation of fulness in his head; he becomes sleepy, and, if the quantity be sufficiently great, he falls into an apoplexy, and dies. From dissections it appears that such as die in this manner have the capillary vessels greatly distended, and even ruptured; the heat of the body is vastly augmented, and even continues some time after death. Hence it is evident, that, by breathing this kind of air, too much sensible heat is conveyed to the blood. In like manner when we breathe the steam of water, if any quantity of that steam be condensed in the lungs, the whole quantity of latent heat contained in that steam discharges itself upon the lungs, and increases the sensible heat of the body; and from this we may learn why on some occasions our sensations should so ill correspond with the thermometer, and why a warm air almost saturated with moisture should always appear much hotter than a dry one, though the thermometer stand at an equal height in both. Oxygen air seems to convey to the blood a much larger quantity of what we have called vital spirit, than any other kind. Whether this vital spirit be the same with the latent heat of the blood, we know not; but, as this kind of air is evidently capable of supplying the blood both with latent and sensible heat, it seems most probable, that, by breathing a considerable proportion of it, both these kinds of heat, as well as the vital spirit itself, will be augmented. In this case, wherever the air naturally contains a larger quantity of oxygen than usual, the blood ought to be mere fluid, as well as warmer, than usual, provided there be no evident cause why it should be otherwise. Accordingly in warm climates it is always found that the blood is thinner and more fluid than in such as are colder; but at the same time the temperature of the body is colder than in other countries. Zimmerman tells us, that, “at Curassau, Europeans gradually lose their fresh colour and vivacity: their natural heat even becomes three or four degrees less than it was at their arrival.” The reason of this last, however, is evidently the excessive perspiration, which is more than sufficient to carry off the superabundant quantity of sensible heat thrown into the body, either by the rays of the sun, or by the superior quantity of oxygen naturally existing in the atmosphere; for it is now found, contrary to the opinions hitherto received, that in the warmer climates the atmosphere contains a larger proportion of oxygen than in the more temperate.[91]

From this discovery it appears, that, whatever may be the cause of the frequency and violence of epidemics in warm climates, it is not the want of oxygen. Nay, we should rather be tempted to think that they were produced by too great an abundance of it; and this the more especially when we know that animals confined in oxygen air are supposed to die of a burning fever; and it is likewise known that this kind of air is prejudicial to consumptive people, and even brings on the disease on those who had it not before. From the experiments mentioned in the note, it seems probable that there are but few even of swampy places in hot climates, where oxygen does not predominate; and in these the heat thrown into the blood must still be augmented by that produced from the quantity of vapour decomposed or condensed in the lungs, which, as the condensation depends upon unknown circumstances, can never be foreseen, or ever prevented, but by a removal from the place.

With regard to other kinds of air, such as inflammable, phlogisticated air, &c. experiments are yet wanting to determine their effects upon people who breathe them habitually. The proportion in which they occasionally exist in the atmosphere on particular occasions has not been ascertained, and from the experiment made by Dr. Priestley with offensive air taken from a manufactory, as well as from Dr. Chisholm just mentioned, the probability is, that, even in the most offensive places, the proportion of azote is by no means so great to the oxygen that we could suppose the excess capable of producing a disorder of any consequence, much less a violent epidemic. Fixed air is always produced in the putrefactive process, and from its quality above mentioned of rarefying and heating the blood, might reasonably be supposed to have some share in producing epidemics, were it not that this kind of air is so readily absorbed by water, as well as a number of other substances, that, except at the very moment of emission, we can scarce suppose it to have any considerable effect.

Mr. Watt in a letter to Dr. Beddoes gives an account of a kind of air, seemingly more noxious than any yet discovered, which he produced by distillation from flesh and from wool. The effects upon himself were so disagreeable that he determined to make no more such experiments, lest he should to his own hurt discover a mode of producing some grievous disease. But we cannot, from an artificial air of this kind, argue to a natural one; as the one produced by Mr. Watt was totally different from any species of air naturally known. All that we can say is, that, as far as we can trace the connexion between our bodies and the different kinds of air which may be breathed, the latter act chiefly by the heat they contain, and which they impart to the body in various proportions; by which means the latent or sensible heat of the blood, and consequently of the whole body, may be occasionally augmented or diminished. Thus the body may be considerably altered in its constitution, and rendered more liable to diseases than it was before; but still it is found that diseases continue to appear at uncertain intervals, though all the causes we are able to discover, or at least all that are constantly evident to our senses, continue to operate without intermission. Though the obvious qualities of air and climate therefore may predispose to an epidemic, we cannot affirm any thing farther: the direct cause is always different, and hath hitherto so much eluded our researches, that we can have little hope of discovering it, except by reasoning from facts less obscure.

8. In all the operations of nature which we have access to investigate, the action of electricity is so much concerned, that we can scarce suppose it to be wanting in any of them. That it is concerned in preserving the health of the human body is likewise certain, if it be the fluid which acts in the nerves, as most probably it is. But whatever preserves health will also bring on disease, if it be applied to that purpose; and we have already seen that this fluid is capable of bringing on the most dreadful symptoms, viz. mortification in its highest stage, fever, convulsions, bilious discharges, lethargy, &c. If it be capable of producing all these, can we say that it is not capable of producing those of an inferior kind, or of varying diseases and symptoms without end, according to the immense diversity of its action? It may be said that this disease was occasioned by a violent stroke of electricity, similar to lightning; but how many people have declared, that, in the beginning of some violent epidemics, they have felt a sudden stroke at the time of seizure! Dr. Hodges mentions this in the plague of 1665 at London, but treats the accounts as effects of a distempered imagination. Procopius relates the same of the plague in his time, viz. that many of the diseased felt a stroke. It is true that they said such strokes were given by spirits in human shape, in which we know they must have been deceived; but, though they were mistaken in supposing that they had been struck by a spirit, it does not from thence follow that they felt no stroke at all. The people mentioned by Dr. Hodges did not say that they were struck by a spirit, yet he treats their accounts with as great contempt as though they had. Where people have no interest in deceiving, we ought certainly to look with a favourable eye upon their testimony; for, even although some part of it should be incredible, we have still reason to believe that there is some foundation for what they say. Thus, the poor sailor, so much frightened at the sight of a large bat in New Holland, was certainly mistaken in saying that he had seen the devil; he was even mistaken in saying that he had horns;[92] but from all this it would have been doing him great injustice to say that he had seen nothing. In like manner, when numbers of people in Procopius’s time said that they were struck by spirits, when we find others in Dr. Hodges’s time saying that they were struck by some invisible agent, when we know that electricity can strike in an invisible manner, it certainly is more reasonable to conclude that violent diseases sometimes do begin by an electric stroke, than that all who said they were struck in this manner were madmen or liars.

It may now again be asked, if the plague, or violent epidemics, be produced by electric strokes, why are they not much more frequently felt, or by what are those milder diseases produced which are not accompanied by any sensible stroke? Here we can be at no loss to say, that whatever produces the highest disease, may also produce the lowest. But, besides this argument, we have positive evidence that commotions in the electric fluid will not only produce sickness, but very extraordinary and seemingly miraculous effects upon inanimate bodies. It has frequently been remarked that people are sick during the time of earthquakes, when the electric matter is in violent agitation. This has been accounted for from the motion of the earth, as the motion of a ship produces sea-sickness. But Dr. Hillary mentions a slight earthquake in Barbadoes where people were affected with sickness and vomiting for some hours after the phenomenon had ceased altogether; which undoubtedly shows, that a certain state of this fluid will disorder the human body, independent of every other circumstance, either of the heat or cold of the atmosphere, or the oxygen, hydrogen or azote contained in it. Again, we find that a certain state of the electric matter is not only capable of producing very extraordinary effects by itself, but also of communicating a power to the human body to do the same. A good number of years ago, a powder-mill near London was blown up. The explosion, as might be expected, was violent and tremendous; but the most remarkable circumstance was, that the electric matter, for a great way round, was thrown into unusual, though invisible, commotions, which discovered themselves by the rattling and breaking of china dishes though sitting apparently undisturbed upon their shelves. This phenomenon did not suddenly cease, and, during the time of it, some people appeared to be infected by an electric contagion; the power of breaking china seemed to reside in their bodies, so that if they approached or touched this kind of ware, it would instantly fly to pieces. Accounts of this extraordinary circumstance were published in many of the periodical works of the time, particularly in Dodsley’s Annual Register; and the fact seems to be established beyond controversy. It proves that what has been advanced by Dr. Priestley concerning electrical operations, on a small scale, holds good also on a large one, viz. that the fluid, when once set in motion, is not easily quieted. It establishes the fact, also, that by great explosions of gun-powder the electric matter is violently agitated; and the consequence of these agitations we cannot know. It may be said, indeed, that in the operations of nature the electric matter is often violently moved without any sickness taking place; neither in fact did any ensue at the time the powder-mill in question was blown up. But it must be remembered, that, in the ordinary course of nature, if the electric matter is moved, a receptacle is also provided for it. In a thunder-storm, where immense discharges of electricity are made from one cloud, there is another cloud of an electricity opposite to the former ready to receive them, or if not, the earth itself is frequently struck. In eruptions of volcanoes, the smoke receives the electricity discharged, and becomes charged with lightning of a more dangerous kind than that of ordinary thunderstorms; and Sir William Hamilton relates, that in the great eruption of Vesuvius, in 1794, lightning of this kind proceeded from the smoke for no less a space than seventeen days. But in artificial commotions of this fluid, where nature has not provided any receptacle, the phenomena must be quite different; and though we may with safety to ourselves interfere with the operations of fire and electricity to a certain degree, yet we may at last rouse these terrible elements into such action as will prove fatal to great numbers. Hence possibly may arise in part some of those sicknesses which take place after battles, in violent sieges, &c. An instance of this is said to have happened at Valenciennes, when last besieged by the Duke of York. A disease prevailed chiefly among women, children, and persons of a weak constitution; great numbers of whom died so suddenly that it was at first thought to be a plague, until it was found not to be infectious. The blood was found greatly dissolved, and the physicians ascribed it to the monstrous bombardment and cannonading which took place during the siege. Such was the account published in some of the newspapers of the time, and from the subsequent considerations it will not seem improbable that such things may take place.

From the experiments of Mr. Bennet (an English gentleman who has made several discoveries in electricity) it appears, that we can neither brush a piece of chalk, open or shut a book, or do several of the most trifling actions, without agitating this subtile fluid in a perceptible manner. It is well known that in some cases we cannot stroke a cat’s back without making the electric matter visible, and in some positions, by putting our fingers near the ears of the animal, very pungent sparks will be received. If then we can neither open or shut a book, if we cannot stroke a cat’s back, or approach a finger to her ear, without agitating the electric fluid, is it reasonably to think we could burn a book, or kill a cat, without doing the same? Certainly it is not. If we cannot burn a book or kill a cat without affecting this fluid, it cannot be supposed that we can burn a house or kill a man without producing a still greater commotion; and in proportion to the extent of our devastations, and the multitude of our massacres, the invisible agitation of this element must become still greater and greater. In all these transactions it must be remembered that the fluid is forced out of its natural mode of action; for electric matter is made for the preservation, not the destruction, of life: but if, by long continued and extensive application of its power to a contrary purpose, we in some measure pervert its action, no wonder that we then feel the consequences of our own proceedings by its partly turning its power against the human race altogether.

Again, the human body is not made for the habitation of an infernal spirit, but for one of a quite different character. The boisterous passions of fury, discord and hatred ought never to disturb the mind, which is made for the habitation of endless peace and joy. The tumultuous passions are enemies to health; and this is so well known to physicians that they are very careful to prevent their patients from being any way ruffled or disturbed by violent passions. It is true these passions act upon the rational soul, which we may suppose to be distinct from that merely animal spirit, probably no other than the electric fluid, which runs along the nerves; but experience shows that each of these can act upon the other; a disorder in the body, particularly in the nervous system, will sometimes disturb the rational soul in such a manner as almost entirely to deprive it of all its faculties; while on the other hand a violent commotion in the rational soul may at once extinguish all the powers of life, as has already been shown from Zimmerman. Now, let any one consider what must be the sensations of those who engage in war. Whatever pity or humanity may be pretended, it is evident that in the day of battle all these sensations must give way to horror and fury on the part of the conquerors, and terror and dismay on that of the vanquished. That these passions never do entirely subside, is evident from the treatment of conquered countries and conquered people. When Jenghiz Khan beheaded his prisoners by hundreds of thousands, when Tamerlane pounded them in mortars, when Khouli Khan caused those who offended him to be carried from place to place, and a piece of flesh to be cut from their bodies at each stage, what must have been the sensations of these miscreants, and those whom they employed in such horrid scenes? On the other hand, what must be the sensations of those who see their dearest relations torn from them and slaughtered or treated even worse than if they were; themselves driven from their peaceable abodes to wander like beasts, while their cruel enemies exult in the miseries they have brought upon them, and glory in doing all the mischief they can, and spreading devastation as wide as possible? Thus, every passion, inimical to health, must, on both sides, be carried to its utmost height; and if these horrid scenes overspread a great part of the earth, for hundreds of years together, is it any wonder that plagues should ensue? If man, forgetting the dignity of his nature, converts the habitation assigned him by his Maker into a kind of hell, and himself into a devil, can we wonder that, in such circumstances, the spirit of life, originally appointed for his use, should become to such a being the spirit of death? Dr. Moseley seems to speak slightly of Helmont for assigning moral causes to fever; but if we consider the matter attentively it will certainly be found that the moral conduct of the human race in general has more connexion with the diseases which befal them, than we are perhaps willing to believe.

Most authors speak of some hidden, unknown and unsearchable power in the atmosphere as the occasion of plagues and other epidemics; and, from what has been already laid down, it seems by no means improbable that this hidden power resides in the electric part of it. But we know that electricity proceeds from the earth, as well as from the air; so that in some countries the evaporation of electric matter from the earth may affect the health of the inhabitants, as well as the constitution of the atmosphere. Hence some spots may be naturally unhealthy, and incurably so, independent of either the perceptible or imperceptible properties of the air; their healthiness may occasionally increase or decrease by means entirely beyond the reach of our investigation. Here then our inquiries must stop. We may indeed make a general conjecture that such differences are produced by the action of the electric matter; but, unless this action be pointed out, and some connexion traced between the situation of the country and a particular mode of action of the fluid, we may as well own our ignorance at once.

9. From all that has been said, then, we may conclude, that none of the obvious properties of the atmosphere, or of any constituent part of it, or of any variation in the proportion of its ingredients, can be accounted the cause of epidemic diseases; that the hidden constitution of the atmosphere may with probability be attributed to the agency of the electric fluid, and that by the action of this secret cause, along with the other more obvious properties of the air, such as heat or cold, moisture or dryness, &c. the human body may be so predisposed to diseases, that they will readily break forth; and that the conduct of mankind themselves may greatly contribute to this predisposition; the question then is, supposing every thing to be thus laid, like a train of gun-powder, what is the spark which first sets it on fire. Does the disease arise spontaneously in the first person affected by it, or does it come from without?

In answer to this we must in the first place observe, that the accounts of all plagues mentioned in profane history trace their progress from one place to another; whence the probability is, that at its origin the disease was confined to a few, perhaps to a single person. In very few cases, however, has it been possible to trace it to an individual; and, even when this has been done, the unfortunate individual is always said to come from some other place. The instance quoted from Dr. Moore is perhaps the only one upon record where the plague arose spontaneously in any person separated from society; and from a single instance little can be inferred. In those terrible examples we have given of people being burned to death without any accident from terrestrial fuel, the agent seems almost certainly to have been electricity. In the plague of Procopius, said not to have been infectious, the strokes complained of by many patients seem to indicate an action of the same fluid. The same in the plague at London, which was infectious, and likewise of others. But, in cases of plagues which are not infectious, another question arises—By what means do such diseases spread from place to place? for even this dreadful pestilence of Procopius did not overspread the earth at once, but is said to have begun at Pelusium in Egypt. To this no answer can be given. To suppose an omnipresent contagion in the atmosphere, proceeding either from contagion or any thing else, cannot be admitted; for upon this supposition the whole world must have been infected at once. The cause, whatever it was, plainly moved from one place to another, or was successively generated in different places. Recourse may be had to the precipitation of the contagious matter of former plagues from the atmosphere; but to account for this in succession will be found very difficult; and the same difficulty will attend every other solution which may be attempted. Mr. Gibbon indeed censures Procopius for supposing it not to have been infectious; and perhaps the spreading of the disease by infection is the only way by which we can account, in a satisfactory manner, for the way in which it diffused itself over the world, which was, by first infecting the maritime places, and afterwards those which were more inland; always visiting the second year those whom it had spared the first.

10. Lastly, to form some idea of the nature of contagion, or infection, as it is more properly called, we must consider, that as the ethereal fluid, acting as heat, pervades the human body, so doth it likewise under that particular modification which we call electricity. Some kinds of air, indeed most of those with which we are acquainted, seem to act by augmenting or diminishing the latent or the sensible heat of the body. Such, when taken in moderate quantity, may produce slight diseases, as head-ach, &c. and, when taken very largely, may even put an end to life at once, either by rarefaction of the blood and rupture of the small vessels, as is the case with fixed air, or by oppressing the lungs entirely with their basis, which cannot be thrown out by the breath as in ordinary respiration. Others may affect the electricity of it, or what in this treatise has been called the vital spirit, as well as the latent or sensible heat. The consequence of this will be diseases of a more serious nature; for upon this principle in all probability depend not only the secretion and proper regulation of the nervous fluid, but what has been called the crafts, or proper consistence of the blood and other fluids. Hence it is possible that such an instantaneous shock may be given to the body, as will not only injure the organization in an irreparable manner, but may be felt throughout the whole body like an electric stroke, even though there be no visible fire, or sensation of burning, as in the case of the Italian priest and others, who perished in such a miserable manner.

Formerly all acute diseases were supposed to depend on morbific matter taken into the body, and absorbed by the blood: the cure was thought to be accomplished by the expulsion of this morbific matter from the body by sweat, or some of the other natural evacuations. The doctrine was attended by many difficulties, and in many cases did not admit of a satisfactory explanation. It was therefore laid aside, and the debility or excitement of the nervous system arose in its place. But this new system admitting of miasmata and contagion, it was plain that morbific matter still kept its ground. With a view, it would seem, to render the nervous theory more complete, it has been found necessary to deny the doctrine of contagion and infection entirely. This has been done, wherever there was a possibility; but the phenomena of the small-pox and measles, as well as those arising from poisons, still militated strongly in favour of morbific matter. To avoid the force of arguments drawn from these sources, the doctrine of absorption was denied, and contagions of all kinds were said to act immediately upon the nervous system without affecting the blood or other fluids. At last the matter seemed to be decided by the experiments of the Abbe Fontana on poisons. He found that some proved fatal by being mixed with the blood, others by being applied to the nerves, and others by being taken into the stomach. Even this did not give satisfaction. It was contended that the effects of poisonous bites were too quick to be accounted for on the principle of absorption; that, after the most violent symptoms had commenced, they might be removed by cutting out the part affected; and consequently that, instead of any absorption by the blood, we were only to believe that the nervous system was irritated.

“Poisons, (says Dr. Girtanner) remedies, and, in general, all surrounding bodies, acting only on the irritable fibre, it follows that they act upon the system in a similar manner, and that every substance capable of producing the greatest possible effect upon the fibre, that is to say, every substance capable of exhausting all the irritability both of the fibre itself and of the system, in an instant, as for instance, laurel water, or white arsenic, is also capable of producing all the inferior degrees of action, either by acting on a fibre less irritable, or by acting upon the same fibre, but in a less quantity. Laurel water, opium, white arsenic, ammoniac, are of course both medicines and poisons capable of healing, as well as of producing, all maladies whatsoever, without exception.[93] And this is confirmed by a number of experiments which I have made upon different animals. This truth seems to me of the utmost importance; and the Abbe Fontana, who made more than six hundred experiments to prove that ammoniac is no remedy against the bite of a viper, would have saved himself the trouble, had he known it. If, instead of applying the venom of the viper to so many animals, and afterwards applying ammoniac to the wound, he had made a single comparative experiment, and applied ammoniac to a wound made by a lancet that was not poisoned, he would have found that ammoniac itself, applied in this manner, would have produced a disease exactly analogous to that caused by the venom of the viper; and, consequently, so far from removing the malady, must necessarily increase it, by exhausting the irritability of the fibre in a much less time than the venom of the viper by itself was capable of doing. Mr. Fontana has made more than six thousand experiments upon the poison of the viper; he employed more than three thousand vipers, and caused to be bit more than four thousand animals; and the conclusion he drew after this truly enormous number of observations was, that the poison of the viper kills all animals, and produces the disease by its action on the blood. But why did Mr. Fontana neglect to make the decisive experiment, the experimentum crucis of Bacon? It is well known that frogs, and many animals with cold blood, live a long time without the heart, and entirely deprived of blood. If therefore the poison of the viper kills animals by its action on the blood, it will not destroy frogs without blood. But experiment contradicts this reasoning. The poison of the viper will kill frogs without blood in as short a time as it kills those animals who have not lost their blood. It is not therefore by its action upon the blood that the venom of the viper destroys animals; and thus does it happen that a single experiment frequently overturns all that six thousand other experiments have apparently established. According to my experiments, poisons operate upon the blood just as they do upon the muscular fibre, by depriving it of its principle of irritability, or of its oxygen. After having made this observation upon the experiments of Mr. Fontana, I must do him the justice to add, that I have found all his experiments very accurate, and that in all those which I have repeated, the result has been exactly conformable to the account given by him; it is in his conclusion only that he appears to be deceived.”

On this I must in the first place observe, that since philosophers and truth seem to be so far distant from each other that even six thousand experiments cannot bring them together, it were greatly to be wished that in their researches they would pay a little more regard to humanity. If the Author of Nature has set man at the head of the creation, if inferior animals must patiently resign their lives to preserve ours, are we therefore authorised to torment and put them to death by thousands for every idle whim that comes into our heads? After Spallanzani, Fontana, Girtanner and a multitude of other learned barbarians had cut in pieces, boiled alive, poisoned and tortured thousands of inoffensive animals, new massacres it seems must be made, and new tortures inflicted, because an experimentum crucis is still wanted! If knowledge is to be obtained only by such means as these, it certainly must be derived from a very polluted source.

2. The experiment on which Dr. Girtanner builds so much is far from being above suspicion. Though we may cut the heart out of an animal, and let it bleed as freely as possible, yet we certainly overrate our abilities if we say that all the blood is taken out of it. The more perfectly an animal is bled, the less irritability it has; which gives a reasonable suspicion, that, if all the blood could be taken away, the irritability would cease entirely. In frogs, and all other cold blooded animals, the blood contains fewer red globules than in such as are warmer; the circulation is more languid than in such as have warm blood, and, of consequence, the blood will retain its irritability for a longer time, and it will likewise be more difficult to deprive the body of all its blood. In making this experiment, therefore, Dr. Girtanner ought to have brought unexceptionable proofs that he had deprived the frog of all the blood it contained. But, as this was not done, we shall be ready to suspect that some was left; in which case we should be still as uncertain as before whether the poison acted on the irritable fibre, or on the blood. But the decisive experiment, or experimentum crucis, seems to have been made by Fontana himself, by injecting a little of the diluted poison of the ticunas into the jugular vein of a rabbit. Here the poison was applied to the blood itself. It could get at no other part of the fibre but the inside of the vein, which is not accounted very irritable; and the quantity injected was so small, that the Abbe thought his experiment had failed; yet the animal died as if by lightning. The moment he turned his eyes towards it, it was absolutely dead, without discovering the least convulsive agony, or other sign of some little life remaining, generally observable for some time in animals killed by the common methods. On applying the same poison to a large nerve of another animal of the same species, no injury followed.

3. The dispute is of no consequence, and the experiment will prove the same thing whether we suppose the poison to act upon the irritable fibre (the nerves and muscles) or upon the blood. The only important point to be ascertained is, whether there be in nature any substance which, applied to the internal parts of the body, or to a wound, will instantly disorder the whole in such a manner as to bring on a violent disease which may prove mortal in a short time. If any such there is, that substance, whether solid or fluid, visible or invisible, may with propriety be called contagion; and if any such proceeds from the body of a diseased person to one in health, the vapour so proceeding is infection. As to the mode of its operation we are little concerned; the sudden manner in which people are affected shows that poisons kill by suppressing in a very short time the principle of life, which seems to be analogous to electricity, or rather the very same with it; neither is it more incredible that the poison of a serpent should kill by disturbing the natural electricity of the body, than that the stroke of a torpedo, or electrical eel, should kill by the same means. The only difference is, that, in the case of poisons, the pernicious substance is introduced into the body itself; in the torpedo, it comes with violence from without. The former we may compare to the silent discharge of an electrified jar by a point, the latter to its discharge with a violent flash by a knob. But that in poisonous bites the blood is greatly affected, and that in a very short time, we certainly know. There are some kinds of serpents whose bites are so suddenly fatal, that no cure can be applied: one of these, called the small laharra, is mentioned by Mr. Bancroft in his Natural History of Guiana. Mr. D’Opsonville, in his Philosophic Essays, takes notice of one in the East-Indies, which he calls the poison serpent or serpent poison, which seems to be as bad as the laharra mentioned by Bancroft. This too is but small, viz. two feet long, and very slender. Its skin is freckled with “little traits of brown, or a pale red, and contrasted with a ground of dirty yellow: it is mostly found in dry and rocky places, and its bite proves mortal in less than one or two minutes. In the year 1759, and in the province of Cadapet, I saw several instances of it; and, among others, one very singular, in the midst of a corps of troops, commanded by M. de Bussy. An Indian Gentoo merchant perceived a Mahometan soldier of his acquaintance going to kill one of these reptiles, which he had found sleeping under his packet. The Gentoo flew to beg its life, protesting that it would do no hurt if it was not first provoked; passing at the same time his hand under its belly, to carry it out of the camp; when suddenly it twisted round, and bit his little finger; upon which this unfortunate martyr of a fanatic charity gave a shriek, took a few steps, and fell down insensible. They flew to his assistance, applied the serpent-stone, fire, and scarifications, but they were all ineffectual; his blood was already coagulated.[94] About an hour after I saw the body as they were going to burn it, and I thought I perceived some indications of a complete dissolution of the blood.”

The bite of the brulan or burning serpent, according to the same author, is almost as terrible. “This is nearly of the same form with the last, its skin is not quite so deep a brown, and is speckled with dark green spots: its poison is almost as dangerous, but it is less active, and its effects are very different. In some persons it is a devouring fire, which, as it circulates through the veins, presently occasions death; the blood dissolves into a lymphatic liquor resembling thin broth, without apparently having passed through the intermediate state of coagulation,[95] and runs from eyes, nose and ears, and even through the pores. In other subjects the poison seems to have changed the very nature of the humours in dissolving them; the skin is chapped and becomes scaly, the hair falls off, the members are tumefied, the patient feels all over his body the most racking pains, then numbness, and is not long in perishing.”

From these accounts it is plain that poisons do operate very powerfully on the blood; and if they do so in one case it is reasonable to think that they do so in all. According to the degree of strength of the poison, however, we are sure that the effects will be more or less visible to us; but, though we should not be able to perceive any alteration whatever in the consistence or colour of the vital fluid, we cannot positively say that it has not undergone any change; for the spirit which operates in it is too subtile for our observation. In the beginning of almost all diseases, perhaps, blood drawn from a vein will not be perceptibly different from that of a person in health; and Dr. Fordyce particularly takes notice of this in fevers; but as the disease goes on, an alteration becomes very perceptible, which gives just ground for suspicion, that there had been some alteration from the very first, though invisible to us.

After all our disputes, however, we shall find that the controversy, though ultimately important, begins more about words and trifles than any thing else. Dr. Brown used the word excitability, Dr. Girtanner uses irritability, and the author of this treatise, the words vital spirit and electricity, to express something equally unknown to them all. The only difference is, that Drs. Brown and Girtanner speak of their excitability and irritability as a kind of power essentially inherent in living bodies, acted upon indeed by certain substances, but incapable of deriving any supply from without; the author of this treatise considers it only as a modification in the human body, or an organization, if we please to call it so, of that fluid which he believes to be universally diffused, under the names of heat, light and electricity. Hence that portion modified or organized in the human body must be under an entire and absolute dependence upon the immense mass of surrounding fluid, and, by any alteration in the motions of it, must be often very perceptibly affected; nevertheless as this fluid was originally created to preserve and not to destroy human life, there is much less danger from a natural than from an artificial commotion in it. In some visible bodies, such as poisons, the fluid acts in such a manner as to counteract the operation of that part which is organized in the blood or nerves, or both. Hence on the introduction of such into the body the disorder flies like lightning through all parts of it, and in a very short time brings on death. In those vapours properly called contagions, the opposite action is less violent, and therefore the disorders they produce are in proportion. Hence such diseases may either be promoted or retarded by the perceptible properties of the atmosphere, which in poisons have little or no effect. There is indeed a remarkable difference in the strength of the poison secreted in the bodies of serpents at certain seasons of the year, or according to their food. M. D’Opsonville observes that the poison of serpents is in general more powerful, the more they live in hot and dry places, where they feed upon insects that are full of saline, volatile and acrimonious particles. But, notwithstanding this difference in the strength of poisons according to the circumstances of time and place, there is not the least reason to suppose that poison of a given strength would not produce the very same effects, let the state of the atmosphere be what it would.

If therefore we certainly know that there are some kinds of aerial vapours which when applied to the human body do exert a power directly opposite to the vital principle, there is no reason to doubt that such vapours may be confined among certain soft substances, such as cotton, wool, &c. and remain there for an unknown length of time, again exerting their malignant powers, when a fresh object comes in their way. Besides, as all kinds of air with which we are acquainted consist of a basis united with the ethereal fluid and volatilised by it, there is reason to suppose that contagions themselves are formed in the same manner. Some kinds of air also are very easily decomposed, in which case the basis attaches itself to some terrestrial substance, the ethereal fluid which volatilised it diffusing itself around in an invisible manner, but generally with a perceptible heat. Fixed air affords a notable example of this; for, by exposing it to lime-water, or even dry lime, alkaline salt, volatile alkali, or common water, a decomposition of the air very readily takes place, and its basis is found to be attached to those substances. What happens to fixed air may also happen to contagion. The basis of it may have a tendency to unite itself to cotton, or such like substances, and thus may not only infect them, but concentrate itself to such a degree as to produce a disease much more violent than that of the person who gave the infection; and something of this kind has even been observed with regard to infected cotton. But now another question occurs: As fixed air, by being attached to terrestrial substances, loses its aerial property, why should the basis of contagious effluvia still retain its malignant quality though in a state of decomposition? Here we are again helped out by analogy. Fixed air is known to be capable of resuming its aerial properties occasionally, from causes unknown to us, though we cannot suppose them to be any thing else than the invisible action of the ethereal fluid so often mentioned; which, being guided by laws unknown to us, we cannot possibly comprehend. The fact, however, is certain, that the basis of fixed air does very often quit the substances to which it is attached, and assume an aerial state in great quantity, and with very mischievous effects. Thus the old lavas of volcanoes, if chemically tried will be found at all times to contain great quantities of the basis of fixed air, but it is only at some times that the mofetes which are supposed to be the air itself, break forth.[96] In like manner the strata under ground always contain great quantities of the aerial basis, but the damps in mines, which are certainly known to consist mostly of fixed air, do not always appear; neither do they gradually accumulate, but come suddenly, spreading unexpected destruction among those who unfortunately come in their way. The same may take place with contagion. After remaining some time in a state of decomposition it may have a tendency to become volatile again, or it may lie dormant entirely; and this last will explain what is quoted from Dr. Russel, p. [178], that sometimes commerce may be carried on with infected places without danger.

Thus we see that the dispute, originally begun about a word, involves at last a matter of the utmost importance; for, if it be found unreasonable to believe that any such thing as contagion exists or can exist, it follows of course that it is also unreasonable to take any precautions against it. Mr. McLean even goes a step beyond those who deny the existence of contagion; for we find him also denying that putrid effluvia can produce epidemics; according to which doctrine, it seems, we may not only safely visit places accounted the most dangerous on account of infection, but live in all manner of filth and nastiness with impunity. It is plain that no person can ever prove that it is impossible for contagion or any thing else to have an existence. Indeed if nothing had ever induced people to believe that it did exist, it would have been superfluous to say any thing about it. But when we have innumerable testimonies to the contrary; when the opinions of the greatest physicians, as Dr. Lind, Dr. Clarke, Dr. Mead, Dr. Sydenham, Dr. Fordyce, Dr. Russel, &c. agree that not only the plague, but every kind of fever, is infectious; when we know from the analogy of nature that contagion may exist; when we know that there certainly are powers in nature able to produce it; is all this to be thrown aside merely on the strength of a theory, and a theory too which can never be proved? for it is impossible to prove the non-existence of any thing, much less the impossibility of its existence. The lives of mankind are too precious to be sported with on philosophical theories; and prudence will always suggest, that wherever danger may at any time arise, there it is proper to be on our guard.

Dismissing at length the subject of contagion in general, we now enter upon the question, Whether doth it appear from fair investigation of testimony, that the plague has, at any time, been communicated by contagion or not? And here I shall confine myself to what has been adduced by Dr. P. Russel on the subject; for, if we find that the disease has only once been introduced by contagion, it signifies nothing though we were able to prove, which we never can do, that it had been an hundred times bred in some other way. The matter is of too great importance to allow even a chance of its importation by the neglect of the precautions necessary to prevent it.

Our author begins with observing, that though the infectious nature of the plague had been a question much agitated in the schools, “it was less to be expected that physicians who had been engaged in practice among the infected should have persisted in the opinion that the disease was never communicated by contagion.” Such, however, has been the case. In 1720 some French physicians laboured exceedingly to prove that the plague which then raged at Marseilles and throughout Provence arose from corrupt humours bred in the body in consequence of irregularity in the seasons, and bad aliment; that it was spread by the same means, in concurrence with terror, grief, despondence, or other debilitating affections of the mind; but was neither bred nor disseminated contagion. Dr. Russel mentions in a note, seemingly with surprise, that “so late as the year 1778, Dr. Stoll of Vienna should have written expressly against the doctrine of pestilential contagion.” To this professor he thinks it a sufficient answer to quote the following passage from Mr. Howard on Lazarettos, “It must appear very strange, that he should go back to Livy’s Roman History for proofs to establish his point, totally neglecting all the facts concerning the numerous visitations of the plague recorded in modern medical books, or which had happened during his own time. I suppose professional men will lay very little stress upon all that can be said on pestilential diseases, in general, which happened in wars and sieges two thousand years ago, as applied to the plague properly so called, a disease then confounded with various others from which the accuracy of latter observations have sufficiently distinguished it.”

Dr. Russel complains of the French physicians at Marseilles having made unfair representations; particularly that while they produce as irrefragable arguments against contagion their own escape unhurt, amid circumstances of supposed danger, they pass slightly over, or omit all mention of numbers of the medical assistants whom they saw perish in the exercise of their profession. M. Dedier, however, who at first opposed the doctrine of infection, at last renounced his opinions so far as to allow that the disease might be communicated to dogs by injecting pestiferous bile into their veins; and he likewise admitted that it might be communicated from one human creature to another, by drawing in for a considerable time the breath of a diseased person, putting on his shirt, lying in the same bed-clothes, and touching the wounded parts of one’s own body with hands embrued with the sweat or blood of one infected. He affirms, however, that the atmosphere of a person in the plague is no more to be dreaded than that of a venereal patient; and that the touching or dressing of buboes or carbuncles is not attended with any danger. He restricts the infectious quality of the humours to the bile; but the inoculation of a person by the matter of a pestilential ulcer[97] undoubtedly decides this point against him.

On the subject of contagion Dr. Russel observes, that the vague manner in which the word has been used has given rise to much confusion. Some, taking advantage of the inaccurate mode of expression on this subject used by Dr. Mead, attacked him with sophistical nonsense. The following may serve as a specimen, from a pamphlet entitled “Distinct Notions of the Plague, &c. by the Explainer.” This explainer observes, that, according to Dr. Mead, “air and his other causes propagate and spread contagion, not the plague; and therefore either contagion and the plague are the same, or else the plague is not considered; if the first, then his causes propagate the plague; and the plague accompanies the plague; an excellent defence! But, if the plague is out of the play, then contagion accompanies nothing.”—From writers like this we certainly can expect nothing.

The opinion of Dr. Cullen concerning contagion has been already noticed, p. [179]; but though he supposes it to be a matter floating in the atmosphere, he observes that contagions are never “found to act but when they are near to the sources from whence they arise; that is, either near to the bodies of men, from which they immediately issue, or near to some substances which, as having been near to the bodies of men, are embued with their effluvia, and in which substances these effluvia are sometimes retained in an active state for a very long time. The substances thus embued with an active matter may be called fomites; and it appears to me probable, that contagions as they arise from fomites, are more powerful than as they arise immediately from the human body.” This opinion concerning the great power of contagion imbibed by certain substances is conformable to what was above laid down by reasoning a priori on the nature of contagion.[98] It is doubted by Dr. Russel, but Dr. Lind adopts it, and Van Swieten gives his opinion to the same purpose. “I am convinced, that the body of the diseased, kept exactly neat and clean, is not so liable to impress the taint, as his late wearing apparel, dirty linen, and uncleanliness of any sort about him long retained in that impure state. I say, these last contain a more concentrated and contagious poison than the newly emitted effluvia or excretions of the sick.”

With regard to the original cause, our author observes, “that the plague is bred or produced originally from vitiated human effluvia, is a matter which has by no means been established on proper authority.” Setting aside therefore inquiries of this kind, he thinks it sufficient to inquire whether the infection be not communicated from a sick to a sound person by immediate contact; whether it be not also communicated at some distance through the medium of the air; and whether substances of various kinds do not imbibe the infectious effluvia, and retain them for a considerable time. So far as these points admit of proof from the experience of times past, the question concerning pestilential contagion will admit of a solution, independent of all theoretic reasoning whatever.

2. On the subject of contagion people have been embarrassed by confounding the true plague with other malignant diseases. This has been done, not only by the ancients, but by some moderns; and our author quotes Dr. Pye, saying “that any epidemic sickness, which rages with more than ordinary violence, and which occasions extraordinary mortality amongst mankind, may be, and is, properly termed a pestilence, or the plague.” By not attending to the proper distinctions, in these cases, circumstances belonging to what are commonly termed malignant or pestilential fevers will often come to be very improperly applied to the true plague.

3. “It may be remarked, that those who contend in favour of contagion, from zeal for accumulating proofs, have collected a number of facts from historical records of very unequal authority, and often with little critical skill in discrimination. Of this error their antagonists availing themselves, have selected from the mass the instances most liable to doubt or objection, and have endeavoured, by their manner of arranging them, to place the whole in a ridiculous light; while more important instances are either evasively past over, misstated in the representation, or invalidated by general declamation on the little credit due to historians in matters of physic, or the prejudices prevalent in ancient times of ignorance, and on contradictions to be found in the arguments of those who support the system of contagion.”

To this the Doctor adds the great quantity of hypothetical reasoning which has been introduced into the controversy, and above all the unfair dealing of the parties in carrying on the dispute, which has reduced the matter from “a calm inquiry in pursuit of truth, to a wrangling contest for victory.” Lastly he insists, that, had it not been for the misrepresentations and sinister dealings of those who have written against contagion, “the question seems to have been properly resolved in the affirmative;” and he complains greatly of the conduct of the Montpelier physicians in this respect, insomuch that “their misstating of circumstances, and the partiality so evidently discoverable in their narrative of cases, will serve more effectually to remove doubts on the subject, than any arguments that could be used against their hypothesis.”

On the subject of contagion our author observes, that some difficulties still remain; but these, though proper subjects of future inquiry, “do not appear to be of force sufficient to invalidate facts already established. It is well known, that the same person who has been inoculated two or three times for the small-pox without effect, even in an epidemic season, has afterwards received the infection upon repeating the operation at a distance of time when the disease was hardly sporadic. The cause of this remains unknown; but ignorance of it was never produced as an argument against the reality of variolous contagion. . . . If, of one hundred persons exposed to the infection of the plague by a near aproach to the sick, ninety should fall sick, shall human inability to assign satisfactory reasons for the escape of the other ten be converted into a positive proof against the disease having been caught by contagion? If persons retired from all commerce with the infected and their attendants, breathing the same air with the rest of the inhabitants, and nourished by the same aliment, remain untouched during the ravage of the plague, as long as they continue secluded, but, upon unguarded communication, are taken ill like others; can any rational doubt be entertained about the cause of their former security? Or if through stealth, or neglect of requisite precautions, substances tainted by the sick should be conveyed into these secluded retreats, and persons living temperately as before, ignorant of what had happened, and consequently in the midst of imaginary security, happen to be seized with the distemper; can it with any show of reason be ascribed, not to contagion, but to terror, or to colluvies in the stomach and bowels, produced by intemperance and bad aliment? The instances here alluded to are not the creation of fancy, but strictly consonant to repeated experience in Turky; to say nothing at present of what has been observed at Marseilles and in various cities in Europe.”

“But a greater difficulty than that of all persons not being equally susceptible of the infection arises from the cessation of the plague, at a period when the supposed contagious effluvia, preserved in apparel, furniture, and other fomites, at the end of a pestilential season, must be allowed to exist, not only in a much greater quantity than can be supposed to be at once accidentally imported by commerce, but in a state also of universal dispersion over the city: the fact, however unaccountable, is unquestionably certain; the distemper seems to be extinguished by some cause or causes equally unknown as those which concurred to render it more or less epidemical in its advance and at its height. In Europe something may be ascribed to the means employed for the cleansing of houses and goods supposed liable to retain the latent seeds of infection; but, at Aleppo, where the distemper is left to take its natural course, and few or no means of purification are employed, it pursues nearly the same progress in different years: it declines and revives in certain seasons, and, at length, without the intervention of human aid, ceases entirely.”

On this we shall remark in general, that the failure of contagion in some cases to produce the usual effects may proceed from some constitution of the body, disposing it not to allow the cause to produce its usual effects at one time, though at another, the constitution may be so far changed as very readily to admit it. This opinion has been very generally received among medical people, who have, to this singularity of constitution given the name of idiosyncrasy. It is, however laughed at by Mr. McLean. “As the fact (says he) cannot be denied, that a great majority have escaped after contact with persons ill of diseases supposed to be contagious, attempts may perhaps be made to account for it by supposing a certain peculiarity of constitution, which exempts from, or disposes to, disease. Is it the many who escape that have this happy peculiarity of constitution; or the few who are seized that are so unfortunate as to possesses it? The former are evidently too numerous to admit such an hypothesis. The property must therefore, I conclude, be given to the latter. But a child here and there is exempted from small-pox, although exposed to its contagion. In order to preserve a consistency, this fact must be accounted for by the same or another peculiarity of constitution. Peculiarities of constitution, then, exempt from contagion in one case, and dispose to it in another; and thus a term, which in reality means nothing, may be made to account for any thing. For my own part I confess my inability to comprehend any other peculiarities of constitution, or idiosyncrasies of habit, than what are constituted by the different degrees of health and disease; the different states of the excitability.”

In the same manner that Mr. McLean argues with regard to disease, let us argue concerning bodily strength. Some men are able to lift a weight of 6 or 700 pounds, but a great majority cannot lift above 300. Whence proceeds the difference? Is it the few who lift the great weight that by nature have more strength, or is it the many who can lift only the smaller that by nature have less? This is precisely his argument, and there needs no other refutation than stating it in this manner. What he calls the states of excitability are as much idiosyncrasies at the time as any thing else. Mr. McLean will not deny that a person debilitated by certain causes is more liable to be seized with typhus fever than one who is not. What does this proceed from, but that the body of the one is prepared for the disease, is constitutionally disposed to receive it, or has an idiosyncrasy of habit disposing to it, which the other has not? It is true, that unless we point out the circumstances which constitute this idiosyncracy we do nothing; but Mr. McLean’s scheme, of resolving every thing into excitability, would forever prevent us from doing so. This is the great deficiency of the Brunonian system altogether; for, by attending only to the animal life of the body, he seems to have absolutely forgot that we had any thing in common with vegetables. The bones, for instance, or indeed any part of the body, cannot be formed by the power which governs it after it was formed. The growth of the human body is as strict vegetation as that of a tree; and therefore we find that after the excitability is entirely gone, after death has taken place for a considerable time, the body still retains its form, and would do so forever, did not other powers interfere with it. Human life therefore is a compound of the vegetable and animal life, the former being the basis of the latter; and it is the vegetable life which is much more commonly the subject of disease than the animal life. In vegetables we observe an idiosyncracy of habit, as well as among animals. Some, even of the same species, are much more vigorous than others, and, among some, diseases are much more common than others. In like manner among the human race some are strong, others weak; in some the blood is much more confident, and coagulates on exposure to the air much more firmly than in others. Excitability, or excitement, is common to all, and the degrees of it (though enumerated by Yates and McLean in a kind of thermometrical scale) must be merely imaginary, because excitability is not the object of our senses. The obvious properties of the body itself, independent of any excitement whatever, are principally to be considered in medicine. These constitute the peculiar constitution, or the idiosyncracy of habit, belonging to each individual. Yet, in defiance of every confederation of these obvious properties, which all have access to observe, the new system leads us only to consider an invisible and unknown being called excitability. Hence diseases peculiar to certain constitutions more than others are said to be occasioned only by certain degrees of excitability common to all, or perhaps to consist in these very degrees themselves. Thus a peculiar mode of practice has been introduced, in which almost the whole materia medica is rejected. We have already quoted Dr. Girtanner, saying that all diseases whatever may be cured, as well as produced, by only four articles; but in the following quotation he goes still farther. “The art of pharmacy and the science of prescription will become useless; a phial of alcohol or laudanum will supply the place of that enormous quantity of drugs which crowd the shops of apothecaries. The trade of the druggist——but hold; if I continue this prophetic language, I shall only expose myself to ridicule,” &c. Reveries of this kind certainly deserve the most severe reproof. People may no doubt amuse themselves with theories as well as any thing else, while these theories continue inoffensive; but when the belief of them leads to a rejection of what has been established by the experience of many ages, they begin to assume a consequence which they originally had not. We have already seen that a disbelief of the doctrine of contagion leads people into a practice accounted dangerous by many, and which cannot be proved to be safe. A total rejection of medicines, the efficacy of which have been attested by thousands, and which never can be proved to have no efficacy, must be attended with still worse consequences, as thus we should be deprived of the means of curing those diseases which our imprudence in rejecting the former doctrine might have brought on. But, to return to the subject of the plague.

The disappearance of the disease, while all the causes that we suppose capable of producing it remain in full force, is a demonstration that it depends on something entirely distinct from the human body, and from all those powers which perceptibly act upon it. It proves that this unknown power has only a temporary existence, coming to perfection at one season, and dying away in another; sometimes capable of being revived, and sometimes not. This corresponds entirely with what has been laid down concerning contagion itself, viz. that like other aerial vapours it is capable of decomposition, and remaining for an uncertain length of time in a dormant state; but that occasionally it may revive, and appear unexpectedly, as mofetes arise from lavas, or damps in mines. After a city has been thoroughly infected with a pestilential disorder, therefore, there can be no security against its re-appearance; it being impossible to know whether the contagion may not be still existing and capable of being revived by some unknown cause, though it has been dormant ever so long. In such cases it may with propriety be said to have arisen spontaneously, though, had it not been there at a former period, there could be no reason to think that it would have appeared at that time.

Dr. Russel next takes into consideration the plague at Marseilles in 1720, of which he says the accounts “are more full, and circumstances better authenticated, than most of the accounts of anterior plagues to be met with in books.” From the opposition to the doctrine of contagion at the time, he also supposes that the facts relative to its introduction would be severely scrutinized, and falsehoods detected: “but (says he) if, instead of such detection, the most material have been passed over in silence, and little more than hypothetical reasoning opposed to others, the main facts may be considered as established, if possible, more firmly than they were before.” These facts are stated as follows: “1. That the plague did not exist in France before the 25th of May, 1720. 2. That it was imported in goods from the Levant, by a ship which left the coast of Syria the beginning of February, and arrived at Marseilles the 25th of May. Two days after her arrival one of the sailors died; an officer of quarantine who had been put on board died on the 12th of June, and a cabin boy on the 23d. Some porters employed in opening the merchandise at the lazaretto also died about this time. Three others were taken ill in the beginning of July, with buboes in the groin and axilla. This alarmed the surgeon of the lazaretto; a consultation was held with two other surgeons on the 28th; the disease was unanimously declared to be the plague, and the three patients died next day: the surgeon of the lazaretto, with part of his family, and the priest who attended the sick, were also taken ill and died.”

From the lazaretto the disease made its way into the city, and began to appear about the 20th of June. By what means it was introduced is not directly said; but it seems to have been by smuggling infected goods. In the beginning of July it began to spread; but a kind of pause having taken place between the 12th and 23d, the physicians were reproached with having mistaken the distemper. During this supposed interval, however, it was discovered on the 18th of July that the disease had spread in a certain part of the city. A surgeon, employed to examine into the matter, declared the distemper to be the worm-fever; and about the 23d the council of health were informed of the death of fourteen persons in that quarter, and of several others falling sick. The surgeon still adhered to his opinion, but a physician declared it to be the true plague. About the end of the month it had got into the suburbs; four physicians declared it to be the true plague, but their report was not believed; they were insulted in the streets, and it was not until some of the inhabitants of better rank were taken ill, that the true state of the matter gained credit.

“Such (says Dr. Russel) was the rise of the plague at first, and its progress afterwards in the months of June and July; whence it appears, that persons on board the suspected ship, those employed in airing the goods, a surgeon and a priest, who attended the sick, were among the first infected; that the passengers from the several ships, all of which ships, the first excepted, brought foul patents, were, together with their baggage, admitted into the city, after preforming a quarentine of little more than eighteen days; that the distemper from the 20th of June till towards the end of July advanced very slowly, and sometimes seemed to pause; that it attacked chiefly the poorer sort of people, and was found in distinct quarters of the city; and lastly, that, during the first forty days, few or none of the infected recovered; a circumstance entirely consonant to what was observed in the beginning of the plague at Aleppo.”

Three other facts are mentioned by our author, viz. that the disease was evidently communicated by infection; that those who were careful to seclude themselves from all communication with the sick and with infected goods, were not infected; and lastly, that the disease, which began to rage violently in August, continued to do so through that and the following month, but declined fast in the months of October and November, and seemed to cease in the middle of winter. Some accidents happened in 1721, between the months of February and July, which gave occasional alarm; but the distemper did not spread, and ceased entirely after the summer solstice of that year.

To all this, however, objections have been made. 1. That the irregular seasons of the former year, a bad crop, and unwholesome aliment, had produced a malignant epidemic, all which, joined to the popular dread of contagion, were sufficient to produce the plague without any imported infection. To this Dr. Russel replies, that these positions, assumed as facts, had no existence; for which he refers to the publications of the times. 2. It was objected that there were instances of the plague in Marseilles before the 25th of May. These instances are only five in number, produced by M. Deidier, “who saw not the cases himself, yet (says Dr. Russel) from the very imperfect accounts he had been able to glean, he thought himself justified in declaring they bore all the marks of the true plague. Nothing (adds the Doctor) but extreme partiality to an hypothesis could have led any one practised in the plague, into such a declaration; the cases bearing every internal mark of belonging to a different class from the plague. I shall endeavour to show this in a few words.

“Of the five supposed infected patients, three recovered, two died, and all had eruptions. One who died had a parotis (the most ambiguous of all pestilential tumours) without any concurrence, so far as appears, of pestilential symptoms. The tumour had appeared six days before the woman’s death, but how long she had been sick remains unknown. The other died the 16th or 17th day, a very unusual period in the plague. She also had a parotis, which did not make its appearance till the 10th or 11th day of the disease. No pestilential symptoms whatever are mentioned. Of the three who recovered, one was very ill with a fever and carbuncle; but neither the invasion nor the duration of the disease are mentioned. Another had a carbuncle and a small tumour on the thigh; and the third (which bears the nearest resemblance to a very slight infection) had also a bubo in the thigh; but the tumours in neither of these patients are described in such a manner as distinguishes them from ordinary tumours; and the apothecary, who gives the account from memory, had in all likelihood never seen a pestilential bubo before.”

“Of the persons infected for some time after the arrival of the ships from the Levant, none had eruptions, and all perished after a few days illness; which agrees entirely with what was observed at Aleppo in the beginning of the plague: hardly any of the sick recovered, and the major part died in three or four days, without any appearance of buboes. Upon the whole, therefore, I think it very clearly established, that the plague did not exist in France before the month of May, 1720. Prior to M. Deidier, however, I find a M. Pons had endeavoured to prove that the plague was in Marseilles, not only before the month of May 1720, but even in the preceding year. I have not had an opportunity of examining that gentleman’s book.”

3. It is objected that the disease was not brought from the Levant by infected goods. “Captain Chataud’s vessel, supposed to have brought the infected goods, arrived with a clean patent, or bill of health, having left the coast of Syria before the plague broke out there; she consequently cannot reasonably be thought to have transported the plague, which was not in the ports from whence she came.”

To this Dr. Russel answers, that on commercial accounts the Turks carefully conceal the appearance of the plague from the Europeans. Should reports of accidents get abroad, they are variously and contradictorily represented, and pestilential marks and tumours fraudulently concealed. Though Chataud obtained a clean patent, the plague broke out soon after his departure, and three vessels with foul patents arrived at Marseilles a few days after Chataud. “To this (says Dr. Russel) it may be further added, that, notwithstanding his clean patent, persons acquainted with the Levant will think it far from improbable, that the plague might actually have been in Sidon when he sailed, though unknown to the magistrate, by whom the patents are granted. . . . A clean bill of health imports that the place has been free from plague, and all suspicion of plague, for a certain space of time; but the clean patents of the two first arriving from the Levant, after the cessation of the plague, are, according to Mr. Howard, deemed foul at Marseilles, and the passengers are obliged to perform a quarantine of thirty-one days. The French consuls lying under an obligation to insert in their patents a detail of circumstances, it must appear strange, when the condition of Syria at that time is considered, how Captain Chataud should have obtained a clean patent.”

Though this must certainly be deemed a sufficient answer to the objection, Dr. Russel goes on to give an account of what had happened the preceding year, when the plague had raged violently at Aleppo; and shows that, from the condition of the whole coast of Syria, a return of the plague was certainly to be expected; that the French consuls could not be ignorant of this, neither could the council of health at Marseilles be unacquainted with what had happened at Aleppo the preceding year. “The facility with which the patents seem to have been issued in Turky, and the partial indulgence of the council to Chataud’s ship, notwithstanding the very extraordinary mortality which had avowedly happened on the voyage, together with their easy confidence afterwards in the reports of the surgeon of the lazaretto, can only be accounted for from the prevailing influence of private commercial interest over a sense of official duty.”

Our author next proceeds to take notice of what happened during this ship’s voyage to Marseilles. On the 31st of January he left the coast of Syria with a clean patent, before the plague broke out. On the 25th of May he arrived at Marseilles, from Sidon, Tripoli and Cyprus. On the voyage, or at Leghorn, he lost six of the crew; but, by the certificates of the physicians of health at Leghorn, these died only of malignant fevers caused by unwholesome provisions. These last words in the Traite de la Peste are said to have been interpolated at Marseilles. At any rate, as Dr. Russel observes, they could relate only to those who died at Leghorn, not to the others, whom the physicians had not seen.

The other account is much less favourable. According to it, Chataud “left Sidon the 31st of January with a clean patent. The plague discovered itself there a few days after his departure. Having sustained some damage by bad weather, he put into Tripoli, where he embarked some merchandise; he took in also some Turks, passengers for Cyprus, together with their luggage. Soon after the ship had left Tripoli, one of these passengers fell sick and died. Two of the sailors employed to throw the corpse overboard desisted at the desire of the pilot, and the rest of the ceremony was performed by the other Mahommedan passengers; the ropes with which the body was lowered down, being by way of precaution thrown into the sea. Within a few days the two sailors who had handled the corpse were taken sick and died. At Cyprus the ship put her remaining passengers on shore, and made a very short stay. Soon after her departure from that island, a third sailor and the surgeon died of an illness of a few days duration. The captain, justly alarmed by these accidents, ordered the bedding and other things used by the deceased to be thrown into the sea; and kept himself carefully separate from the crew during the remainder of his voyage. Some time after this three more sailors fell sick, and, there being no surgeon on board, the vessel put into Leghorn, where the three sick men died, and the physician and surgeon of the lazaretto declared the disease to be a malignant pestilential fever.”

Our author considers the above account as a full proof of the plague being imported by Chataud’s vessel: he declines entering into the question about the possibility of importing contagion in merchandise. How this might take place has already been explained; and the present instance of its having been imported is as clearly proved as can be expected. A collateral proof, with regard to the contagion of the small-pox, we have from Dr. Huxham. A beggar, ill of that disease, approached a certain town in England, but was not suffered to enter, for fear of infection. The beggar died, and the infected clothes were burnt at some distance from the town; but the smoke being blown upon it by the wind, the small-pox in a short time made its appearance, beginning in that part upon which the smoke was blown. This clearly proves that one species of contagion may adhere to clothes, and is a very strong presumption that any other may do the same. It also shows that contagion, when once produced, is by no means easily destroyed; and consequently that all kinds of purification, even when used with the utmost care and diligence, are scarce sufficient to ensure safety.

It would now be superfluous to enter farther into the subject of the plague being communicated by infected goods, did not our author quote a work of Dr. Pye of London, in which the latter from the very Journal (which has been used as containing arguments in favour of contagion) makes inferences directly opposite. “The facts related in this journal (says Dr. Pye) seemed to me to make so clearly against the modern doctrine of contagion, that if this writer had not mentioned them as undeniable instances in his favour, I should not have thought there had been any persons here in England so dull of understanding, or so much blinded with prejudice, as to stand in need of having these facts put into a more obvious light: but, having this occasion, I shall consider them more largely than otherwise I would have done, and show that the porters, who died in the lazaretto at Marseilles, received no hurt or infection from the goods.

“To leave no room for objection, I shall take notice, that a guard of quarantine died on board Chataud’s ship the 12th of June; but, as this officer was no ways concerned either in unloading or opening the goods, he could receive no hurt from them; and besides, this must have been fourteen or fifteen days after the goods had been carried out of the ship into the lazaretto. Further, six of their men are said to die at Leghorn; but the town of Leghorn was not infected from thence, which would have been more likely if there had been any infection in the case, than that Marseilles should be afterwards infected.

“If any infection or infectious aura can be supposed to be packed up, and brought in goods, such infection or infectious aura must necessarily issue forth from them in greatest abundance, and with the greatest force, at the first opening or unpacking of them; and, as it must continue to fly off every moment, and be thereby continually diminishing, it is likewise certain, that in a very few days the goods must be in a great measure, if not entirely, cleared of it. Wherefore, if the porters could have been infected from the goods at all, it must have been at the first opening of them: but, even according to this journal, the porters that first fell sick were not taken ill before the 23d of June, whereas Chataud’s ship arrived the 25th of May preceding; so that the goods of that ship, in purifying which the porter first mentioned was employed, had been airing and purifying for twenty-six or twenty-eight days before this accident happened; and it cannot be conceived that after so long a time they should not have been entirely purged of all infection or infectious aura, if any could have been brought with them. Or if it can be supposed, which I think impossible, that any part might still be left, it must withal be supposed so much less than at first, as not to be capable of doing, those porters especially, the least hurt: to suppose otherwise would be to argue that the same man who some days before had received and borne a very great quantity and force without any injury, could then be killed by a quantity and force infinitely less.

According to the report of merchants, Frenchmen are not subject to the plague in Turky; and it cannot be conceived that so small a quantity of infectious air as can be packed up and brought in a bale of goods, should destroy them in France, or in an air and climate distant and different; when the whole atmosphere of the same infectious air is found not to injure them in very infected places, and wherein it is allowed to be bred and generated.”

Thus far Dr Pye.—Let us now hear Dr. Russel in answer.

“The death of the quarantine officer was mentioned in order to leave no room for objection; but still it may be objected that he has omitted the death of the sailor on the 27th of May, and asserted, in contradiction to the journal, that the former six sailors died at Leghorn. That Leghorn was more likely to be infected than Marseilles, is a strange notion. The ship had landed no goods there, nor had any intercourse with the shore; for the physician who visits the sick on board, remains at a distance from the ship, in a boat, and the dead bodies are sunk in the sea. As to the circumstance of the goods of Chataud’s vessel being all in the lazaretto before the 12th of June, it is a supposition to be attributed to Dr. Pye’s unacquaintance with matters of that kind; for it is impossible a ship which arrived the 25th of May should discharge the whole of her cargo in two or three days. The dispatch would have been miraculous, considering the ship lay near two leagues from the lazaretto, and was unloaded, and the boats navigated, by her own crew. It did not occur to Dr. Pye, that some time, previous to the vessels beginning to unload, is taken up in examination and other forms at Pomegue, and the council of health. The loss of six men on the voyage was an extraordinary circumstance, that required deliberation; and it appears that on the 29th, after the death of the sailor on board Chataud’s vessel, the council determined the quarantine of his cargo to be forty days, commencing from the landing of the last bale; which was double the time usually allowed for a ship with a clean patent. It is very probable, therefore, that the ship did not begin to unload till after the 29th of May, and possibly had not finished when the quarantine officer died, the 12th of June, who must have been taken ill two or three days before.

“In regard to the time requisite for the complete evaporation of the infectious aura, in what proportionate gradation its activity is impaired by ventilation, and the specific quantity required to produce effect on the human body, they are matters which I apprehend will not readily be admitted to be clearly and certainly known. That the first porters were not taken ill before the 23d of June, is very true; but that the goods had been airing and purifying for twenty-six or twenty-eight days, has been shown above to be an error. The Doctor also makes two other suppositions equally erroneous. The first, that the whole of the cotton contained in a number of bales is equally imbued with infectious aura; the second, that all the bales of a ship’s cargo are opened nearly about the same time. But, as the cotton contained in these bales may not only have been collected from different villages at different times, but packed up under various circumstances relative to the materials used for embalage, and the persons employed in embaling or steeving them; it may easily be conceived how the cargo of a ship, coming even from a place where the plague actually rages, may be only partially infected, or not infected at all. The warmest advocate for contagion never contended for every bale of a ship’s cargo being equally infectious. As to the airing of the bales, it is a laborious and a tedious process. Where there is a considerable number, it takes up several days to open and arrange them, goods of different kinds must be disposed separately, accounts taken, and the cordage, &c. laid up with care where it may be found again. The laborious part of these operations is performed by the porters, who also transport the goods from the water side to the enclosure where they are to be aired: and, as the days of quarantine do not begin to be reckoned till all the goods are landed, the porters for some days at the beginning are sufficiently employed in receiving and arranging the cargo, that being the business requiring the first dispatch. When these circumstances are considered, it will appear no extravagant supposition, that some of the last opened bales of Chataud’s cargo might still retain enough of infectious aura to infect the porter on the 23d of June. To set this retardment, almost unavoidable in the opening of bales, in a still clearer light, it should be observed, that, by the regulations at Marseilles, all suspected goods are subject to what is termed sereines; that is, a certain number of bales are taken out of the hold, and, being opened at both ends, are exposed to the air for two, three, or six days, by way of trial, in order to see if any signs of infection should appear among those employed in handling the merchandise. When these have been aired, more or less, according to circumstances, another parcel is opened and exposed to ventilation in like manner: so that, according to the burden of the ship, there may be several of these sereines, each of several days duration. In this manner, independent of accidental impediments from wind and weather, in sending the goods from the ship, it maybe supposed, were it at all necessary to make the supposition, that the porters, not only on the 23d of June, but on the 7th and 8th of July, were infected upon opening some new bales. As to the porter being infected by goods from another ship, Dr. Pye thinks it impossible, because the ship had been twelve days in port, and the goods must have been eight or nine days in airing and purifying: had he been acquainted with the practice of the sereines in quarantine, he would have been at no loss to make the accident agree exactly with his notion of the infectious aura. . . . The plain matter of fact, as it stands in the journal, is this, that six porters, employed in purifying suspected merchandise from the Levant, died of the plague; and their death was followed by that of the surgeon who attended them, and part of his family.”

From this the reader will be able to judge how far the question is decided in favour of the fact that the plague at Marseilles was actually produced by imported contagion. It seems needless to follow our author through his investigation of those facts which his adversaries have misrepresented; for these must of course be in his favour; every misrepresentation by a disputant being plainly an abandonment of his cause. Indeed the argument against contagion at that time was properly but one, and is set forth in no stronger language now than formerly. Even as long ago as 1665 Dr. Russel quotes one Gadbury an astrologer stating the difficulty as strongly, and giving a solution of it as clearly, upon his principles, as the best modern theorists can do upon theirs. “If the pestilence, (says Mr. Gadbury) be infectious, and really catching in itself, it must be so equally to all persons that approach it, or that it approacheth; or else it must be infectious to some particular persons only. If it be infectious to all persons, or catching to all alike, then all persons, that come into the sight or within the scent of it, must necessarily be subject unto it. If not infectious unto all, but unto some particular persons only, I say then it ought not to be deemed or esteemed infectious at all, at least not any more infectious than are all other diseases, viz. small-pox, scurvy, pleurisy, ague, gout, &c. since (though the notion of infection be laid aside) there is not a person born into the world that hath not at some time of his life (as his nativity shall truly show) some one disease or other. Never was any person subject to violent diseases, as plague, &c. but had a violent nativity to show it, and e contra.”

The answer to this has been already given.—Let any other cause than contagion or infection be supposed, and the difficulty remains equally great. The probability is in favour of contagion, rather than a general disposition of the atmosphere, because in the latter case the disease would, contrary to experience, begin in a great many places at once; but the plague begins in such a secret manner that we scarce know whence it comes. Like fire, or a ferment in liquors, it diffuses itself far and wide, and lastly, like an immense inundation, the source of which is dried up, it seems to lose its power by extending too far, and dies away altogether. We cannot penetrate into the causes of those things, but, without any speculation at all, we can observe that the disease falls upon people of a certain constitution more than others, and this may be of use in preserving ourselves from it, as shall be explained in the next section.

It is still necessary to say something of the infection spreading from one person to another, and being kept off by refraining from communication with the diseased. This indeed naturally follows from its proceeding originally from the cotton: for as all the infected did not touch this cotton, there can be no other cause assigned from its spreading than by communication from one to another; and, therefore, if such communication was cut off, we should naturally think that the disease would not spread. But, in opposition to this, we have already quoted Dr. Moseley giving a long list of convents infected, though they kept themselves strictly shut up. Dr. Russel cites, in favour of prevention by shutting up, two certificates, one by the bishop of Marseilles, the other by the sheriff of the same place. To these he adds the testimony of M. Langeron, who was actively employed throughout the whole time that the plague continued, first as a commodore of the gallies, and afterwards as governor of the town and its dependencies. In opposition to these, however, he takes notice of two passages “in books of acknowledged authority,” which he is at pains to answer; the one is from the Journal already quoted, which says, “and what is unaccountable, those who have shut themselves up most securely in their own houses, and are the most careful to take in nothing without the most exact precautions, are attacked there by the plague, which creeps in no one knows how.” The other passage is taken from the Relation Historique, “that, in the height of the pestilence, the infection penetrated into places which had till then remained inaccessible; that monasteries and houses shut up in the most exact manner were no longer places of security.”

To the former of these our author answers, that “from the manner of stating the case, one would think that all these religious had been close shut up, without any communication with persons without doors; and this was certainly intended by an author who has made remarks upon it; but it will be found, upon looking into the beginning of the very paragraph cited, that the greatest part of them are represented as martyrs who had meritoriously exposed themselves. Of the twelve different orders mentioned on this occasion, the Grand Augustines only are said to have kept in their convent. But, supposing the Augustin convent to have been actually shut up, and in that state infected; it would by no means invalidate the instances brought of the preservation of the convents, the certificates concerning which were granted deliberately, after all was over; whereas the journal, written from day to day, marking circumstances rapidly as they occurred, the author, amongst various other affairs, had not always leisure or opportunity to examine minutely into circumstances. It is in this light I am inclined to consider the houses being infected which took in nothing without the most exact precautions; and the rather, because I met with several instances of the like kind at Aleppo, in the houses of the Christian and Jewish nations: but in the sequel it generally appeared there had been some improper communication carried on by the domestics, unknown to the family at the time.”

“That the atmosphere, in a city so dreadfully circumstanced as Marseilles, may become so highly tainted as to convey the plague into houses shut up, cannot confidently be affirmed to be impossible, by those who hold mediate contagion; and the concurrence of circumstances at that period in Marseilles, renders it highly probable that such accidents happened. But, in general, the pestiferous effluvia once emitted into the air, do not appear to operate at any great distance from their source; and M. Deidier asserts, that two monasteries (from their situation, one near a burial ground, the other near a pest-house) very dangerously situated, remained nevertheless untouched, which he thinks an argument against infection being conveyed by the air.”

From this long and contested account of the manner in which the plague was received into Marseilles, we see how very difficult it must be to come at a true state of facts, when a number of people think it their interest to misrepresent or conceal them. The limits of this treatise will not allow us to follow our author through the numerous details of misrepresentations and unfair methods which the adversaries of the doctrine of contagion have made use of to establish their opinion: neither shall we enter into any discussion concerning the origin of other plagues, as we should in them find the same opposite kinds of evidence without such documents for distinguishing the true from the false as Dr. Russel has produced in the case of Marseilles. A single fact only, mentioned by Mr. Howard in his Treatise on Lazarettos, shall be related, and which, if allowed to be fact, decides the question as effectually as a thousand.

“When the plague raged at London in 1665, it was conveyed to the remote village of Eyam near Tideswell in Derbyshire. In this place it broke out in September 1665, and continued its ravages upwards of a year, when two hundred and fifty of the inhabitants had died of it. The worthy rector, Mr. Mompesson, whose name may rank with those of Cardinal Borromeo of Milan, and the good bishop of Marseilles, at its breaking out, resolved not to quit his parishioners, but used every argument with his wife to quit the infected spot. She, however, refused to forsake her husband, and is supposed to have died of the plague. They sent away their children. Mr. Mompesson constantly employed himself, during the dreadful visitation, in his pastoral office, and preached to his flock in a field, where nature had formed a sort of alcove in a rock, which place still retains the appellation of a church. He survived, and the entries in the parish register relative to this calamity are in his own hand writing, viz.

In 1665,	Sept.	Died 6	1666,	May	Died 5
	Oct.	22		June	20
	Nov.	5		July	53
	Dec.	7		Aug.	78
1666	Jan.	3		Sept.	14
	Feb.	5		Oct.	17
	March	2		Nov.	1
	April	12

This plague is said to have arisen from a box of clothes sent from London while the distemper was at its height in that city. But whether this be admitted or not, it cannot well be supposed that in a small village there could either be a peculiar constitution of the air, collections of filth, immoderate heat, cold, or in short any general cause from which a plague could be supposed to arise, that would not have affected the country for a great way round. How then came this insulated spot to be so violently affected, except by contagion? No matter whether by clothes or any thing else. The very particular manner in which the numbers who died are recorded, leaves no doubt as to the fact of the distemper having been there; neither is it possible to account for its rise on any other principle than contagion.

Mr. Howard, previous to his going abroad, had been furnished, by Dr. Aikin and Dr. Jebb, with a set of queries relative to the plague, to be put to the physicians in the different countries through which he travelled. This commission he executed with great fidelity and exactness. The physicians to whom he proposed them were, Raymond of Marseilles, physician; Demollins of do. surgeon; Giovanelli, physician to the lazaretto at Leghorn; They, to do. at Malta; Morandi, physician at Venice; Verdoni, at Trieste; Jew physician at Smyrna; Fra. Luigi di Pavia, prior to the hospital of San Antonio at Smyrna. The questions proposed were as follow:

1. Is the infection of the plague frequently received by the French?

Though this was not asking in direct terms whether the plague is infectious or not, all to whom it was proposed seem to have viewed it in this light, Raymond of Marseilles only excepted, who answered directly, “Sometimes it is.” All the rest, except Giovanelli, agreed that it might be communicated by the touch, or by the breath. Verdoni gave an instance of its being communicated by a flower which three persons smelt at; two remained free, but the third sickened and died in twenty-four hours.

2. Does the plague ever rise spontaneously?

In this Verdoni alone answered positively in favour of the spontaneous rise of the plague. They spoke ambiguously.

3. To what distance is the air infected? How far does actual contact, wearing infected clothes, or touching other things, produce the disease?

To this question Verdoni answered in a manner seemingly inconsistent with his former answer; allowing not only that the plague was infectious, but that infected things might communicate the disease after an interval of many years. All agreed that the strength of the infection was greater or less according to circumstances; the distance at which it could act was likewise uncertain. Raymond said that the sick might be safely conversed with, across a barrier, at a few paces distance; the Jew said at two ells distance, provided the chamber windows be not all shut. Giovanelli said it had been proved that the infection did not extend beyond five geometrical paces. The touch of infected clothes, or drawing in the breath of the sick, was looked upon by him and Fra. Luigi to be very dangerous.

4. What are the seasons in which the plague chiefly appears; and what is the interval between the infection and the disease?

To this it was answered by Raymond, that the two solstices are the times in which it has least power. The others agreed that hot and moist weather was favourable to its ravages; the spring, summer and first month of autumn are dreaded. These circumstances, however, must be variable in different countries. As to the time in which the infection shows itself, the answer was various. According to They, it “sometimes acts slowly, sometimes like a stroke of lightning.” According to Verdoni, “the disease generally shows itself at the instant of touch, like an electrical shock.” Sometimes the infection will be communicated from a sick person to a sound one, who without any disease may communicate it to a second, and that second to a third, in whom alone it would become active.

The other questions, relative to the symptoms, prevention and cure of the distemper, will be taken notice of in the course of the treatise. In the mean time having discussed, with a prolixity almost exceeding our bounds, such preliminaries as seemed most likely to throw some light on the nature of the distemper, we shall now proceed to the medical history of the plague, as we find it laid down in different authors.

Though this distemper has most frequently been accounted a fever in the highest degree, yet, as we have already noticed, it seems to be essentially different.[99] The testimonies there quoted are sufficient to establish the fact; and, were it needful, many others might be brought from authors both ancient and modern. In the plague said to have taken place in the days of Romulus,[100] Plutarch relates, that the people died without any sickness. To this very ancient testimony we shall add that of Dr. Patrick Russel, who closes the account of his first class of patients with the following paragraph: “That the plague, under a form of all others the most destructive, exists without its characteristic eruptions, or other external marks reckoned pestilential, can admit of no doubt; and it is to be regretted that mankind have so often, from the absence of these, been betrayed into errors of fatal consequence on its first invasion; at which early period human prudence can only be exerted in the way of defence with any probability of success.”

The symptoms of this fatal disease were sometimes a sudden loss of strength, confusion or weight in the head, giddiness at intervals, oppression about the præcordia, dejection of spirits, taciturnity, an anxious aspect, but without any symptoms of fever. In these, death ensued within twenty-four hours; some were said to have died within a few hours, but our author saw none of these, and is inclined to doubt the truth of the accounts, having in several instances, where this is said to have happened, found upon inquiry that matters had been inaccurately stated, and that the patients had really been ill one or two days.

In others the disorder was more perceptible. In a few hours the eyes became muddy, the surface of the body cold, with drowsiness, lethargy, and pain at the heart. In the progress of the distemper they frequently lost the power of speech, the skin seldom recovered its warmth, or, if it did, it was only by irregular flushings. The pulse sometimes remained nearly in its natural state, but was, for the most part, low and quick. They were “by turns delirious, confused and sensible, but the comatose disposition was most prevalent. Towards the end they suffered extreme inquietude. Vomiting in some occurred the first night; in others a diarrhœa next day; both accelerating the fatal period; but these symptoms were less frequent than in some of the other classes. Buboes appeared only in a very few who survived the third day. . . . The total absence of buboes in such patients as perished suddenly I have no doubt of, nor of their being in general very rare in others of this class; though I suspect that the buboes might sometimes have been concealed, where the disease ran out to the fourth or fifth day, and for the same reason that the reports concerning the state of the corpse were sometimes not true. . . . It was very rare to find suspicious marks of infection on the bodies [of those who died within 24 hours]. . . . Carbuncles were seldom visible till the month of May, which was later than this form of the disease. It prevailed chiefly at the rise of the plague in 1760, and its revival in the two succeeding years, decreasing as the distemper spread; and though they were found dispersed in every stage of the pestilential season, yet the number of this class was proportionably small, compared with that of others. Petechiæ, vibices, or broad, livid, roundish spots, occurred sometimes, but were not common, and the two latter were seldom visible till after death.”

This account of the most malignant form of the pestilence differs considerably from that of Dr. Hodges, who seems to think that the tokens, as he calls them, very generally were to be found on the bodies of those who died suddenly. He mentions indeed a young man who was suddenly seized with a violent palpitation of the heart, and thus continued till his death, which took place in a few hours. In this case the Doctor supposed that there might be a carbuncle broke out on the heart. Dr. Russel has considered the description of the tokens given by Dr. Hodges, and compared it with that of others called by Diemerbroeck maculæ mortis, spots or tokens of death; and by this comparison it appears that the former has spoken somewhat indistinctly on the subject, confounding two different kinds of eruptions together. Dr. Hodges, however, as we have already seen (p. [10]) asserts, in his Loimologia, that the tokens rise from within, and are broadest at their bases, where he also supposes the pestilential poison chiefly to lie. To the same purpose, in his Letter to a Person of Quality he says, “The tokens have their original and rise from within, and afterwards externally show themselves; which is evident, because the basis of them is larger than their outward appearance, and the internal parts are found very often spotted, when there is no discoloration visible on the skin.” Dr. Russel, after quoting Diemerbroeck, makes the following observations: “The author (Diemerbroeck) is diffuse on this subject, and thinks it a mistaken though prevalent notion, that the maculæ are merely superficial in the skin, proceeding from putrefaction, ebullition, &c. in the blood or humours: on the contrary he affirms, they arise from the internal parts, even the periosteum, broad at the base, and tapering to their termination in the skin, being produced by the extinction and extravasation of the vital spirits. Now (says Dr. Russel) this answers exactly to one species of the tokens described by Hodges, which therefore may be reckoned the same with the maculæ mortis, and was probably the only one observed at Nimeguen,” &c. On the same subject he quotes a book entitled Medela Pestis, in which the author says that by careful dissection the tokens may be traced half-way deep in the flesh, and some, in the muscles of the breast, have been followed by the incision knife even to the bone. By the directions given by authority to the searchers in 1665, they were ordered to look narrowly for these tokens, which were described as “spots arising on the skin, chiefly about the breast and back, but sometimes also in other parts. Their colour is something various, sometimes more reddish, sometimes inclining a little towards a faint blue, and sometimes a brownish mixed with blue; the red ones have often a brownish circle about them, the brownish a reddish.”

On the subject of tokens Dr. Hodges further observes, that they differed also in their degrees of hardness, some being easily penetrated with a needle or penknife, while others, more callous or horny, were penetrated with more difficulty. They so strongly resembled warts, that they could scarce be distinguished from them; and Dr. Hodges himself was often obliged to have recourse to a needle for this purpose. They seemed hard to the touch, not unlike kernels under the skin, the superfices being smooth. “When I essayed to prove some of them (says he) I found them almost impenetrable.” Another very remarkable circumstance relative to them was, that they were often quite insensible, and this distinguished them from the carbuncle, which is always very painful. Hodges also remarks, that a quick sensibility in the skin was always a good sign, and those that went no farther than the skin would sometimes slough off.

Along with these tokens we can scarce doubt that petechiæ and vibices made their appearance. The former, even in the inferior degrees of the distemper, were dangerous, the latter always fatal, never appearing till the patient is within a few hours of death, sometimes indeed not till death has taken place. Of the petechiæ Dr. Russel says, that for the most part they predicted death, but not without exception. Such as he observed were round, somewhat smaller than a recent flea-bite. They were distinct, few in number, and scattered irregularly about the breast and mastoid muscles. When they did not appear till the approach of death, they were from the first livid, or very dusky; but if they appeared early, they were of a less deep colour, changing afterwards to livid. Hodges speaks of them as deeper coloured than the spots of malignant fever, not fixed in any particular spot, sometimes few, but commonly very numerous; the colour sometimes red or purple, sometimes yellow, and sometimes livid or black. From Gotwald, Russel quotes a description of these spots, which he divides into four species. 1. Reddish, like flea-bites, soon growing brown or black; appearing on all parts of the body except the face. 2. In the form of lentils, spreading like the former all over the body; ruddy at first, but in 24 hours growing dark or ash-coloured. 3. Large brown spots, scattered here and there, sometimes intermixed with the lentil kind. 4. Not unlike the measles, spreading all over the body, rising afterwards in small blisters without any matter, vanishing about the fifth day. Russel also takes notice of a species of petechiæ which were very numerous, confluent, and of a dark red or dusky colour and irregular figure. These were sometimes remarked in the interstices of the former. Such instances occurred but rarely.

The vibices were much larger than the petechiæ. Gotwald says that they covered the face as high as the nose, and from thence spread to the forehead, disfiguring the patient in a frightful manner. They did not appear till a short time before death. Often they appeared unexpectedly, shooting up like lightning from the breast to the face, in spots of various colours, blue, green, brown and yellow. Diemerbroeck describes them as oblong spots of a livid or black colour, like strokes drawn with a pen; sometimes they were larger, the biggest resembling the strokes of a whip. Russel takes notice of a kind of marbled appearance which took place at the height of the disease, or a few hours before death; the colours being a faint blue, and darkish red, both more or less obscure at times, but never bright. It was not permanent, vanishing in one place, without leaving any trace, and returning at short intervals. “The skin in various places was sometimes deformed by narrow streaks of reddish purple, or livid colour. When such took possession of the face they gave a frightful appearance to the countenance, and frequently made such an alteration in the features, and so completely disguised the patient, as to render him hardly knowable by his acquaintance. A streak nearly of the same kind was sometimes observed darting from the edges of the buboes and carbuncles. The vibices or weals were much longer and broader, and more exactly resembled the marks left in the fleshy parts by blows or stripes; they were found chiefly on the thighs, buttock, and back, and made their appearance several hours before death, in some cases, but in others not till after. Large blue or purple spots, the maculæ magnæ of authors, were sometimes observed with or without the vibices, a little while before the patient expired, but most commonly were discovered only on the corpse. Their figure in general was round, sometimes irregular.”

Whether all these mortal signs appeared on such as died very suddenly of plagues, and were by the English writers confounded under the general name of tokens, cannot certainly be determined. Dr. Russel saw none who died within the twenty-four hours, and few who died within thirty hours, so that we cannot from him expect any particular account of the situation of those who died suddenly. In general, however, he says, that “in the most destructive forms of the plague, the vital principle seems to be suddenly, as it were, extinguished, or else enfeebled to a degree capable only for a short while to resist the violence of the disease; in the subordinate forms, the vital and animal functions, variously affected, are carried on in a defective, disorderly manner, and denote more or less danger accordingly.” It seems probable therefore that in those who are suddenly killed, the same effects take place in a short time which are observed to take place after a longer space in those who die gradually, buboes only excepted, which require for their formation a longer time than is allowed to the patient to live. Internal mortifications, or rather eschars, are therefore to be suspected, and dissections have evinced that this was really the case; but besides these there was an appearance observed in the plague at Marseilles which is not taken notice of by former physicians; viz. a preternatural enlargement of the heart. M. Deidier on that occasion communicated an account of nine dissections, but of these only one had died without eruptions. This was a woman of 40 years of age, who lived till the third day. In her “the mediastinum[101] was torn towards the upper part; the pericardium of a livid colour; the heart larger than in its natural state, by the swelling of its ventricles; full of thick, black blood. The liver was also very large, and of a livid colour, with a carbuncular pustule on the side of the gall-bladder, which was filled with very black bile.” In others who had eruptions, and who of consequence we must suppose to have lived longer, the enlargement of the heart was still more remarkable. In one who lived eleven days, the heart was of double the bigness, having scarce any blood in the ventricles, whose cavities were filled each with a large polypus, that on the right side having dilated the auricle to the breadth of four inches. The liver also was larger than ordinary, and the gall-bladder full of a black and green bile. The appearances were much the same in all the rest, but, as the time they sustained the disease is not mentioned, we cannot determine whether the enlargement of the heart took place at the very first, or was only an adventitious symptom after the fever had come on. Dr. Russel takes notice that such patients as he attended complained greatly of their heart. “A sense of oppression about the præcordia (says he) which the sick were at a loss to describe, was, in one degree or other, a constant attendant on the plague, except in very slight cases of infection; and where it came on early, or persisted in a high degree, was always a dangerous symptom. The sick showed how severely they suffered by their perpetually changing their posture, in hopes of relief; but, when asked where their pain lay, they either answered hastily they could not tell, or, with a fixed, wild look, exclaimed kulbi! kulbi! (my heart! my heart!) This anxiety increasing as the disease advanced, terminated at length in mortal inquietude, the patient, for many hours, in the last stages, incessantly writhing his body and limbs as if in agony. Though pain at the heart was often conjoined with the symptom just mentioned, and by the sick seemingly blended together, it appeared to be different, and to exist separately. They often exclaimed as in the other, my heart! my heart! pointing also towards the scrobiculum cordis, but then would add eujani kulbi, my heart pains me; or naar fi kulbi, my heart is on fire.” This last pain the Doctor supposes might have its seat in the upper orifice of the stomach; the extreme anxiety may be accounted for from the enlargement of the heart; but as neither of these symptoms took place in such as died in a very short time, we must be apt to consider this enlargement not as any primary and essential symptom of the disease, but as one which takes place when the vital powers are able to oppose for some considerable time the cause of the disease.

In his account of the origin of the plague, Dr. Russel takes notice of the opinion that, at the communication of the infection, the sick were sometimes sensible of having received it. This has been observed by Dr. Lind in malignant fevers; it has also been observed in plagues, as we have seen from Dr. Hodges, Verdoni, and others; but Russel says he never saw any instance of this. He owns, however, that he has seen instances of the disease quickly succeeding a panic fear of being infested. “In cases (says he) where the disease was not discovered to be the plague, till upon the eruption of buboes after two or three days, I have known several persons who had, till then, without the least suspicion, frequented the sick, struck suddenly with a panic, and imagine themselves ill. They felt shooting pains in their groins, confusion in the head, and a loathing. Though in some these complaints were merely imaginary, and soon vanished, in others they proved real; the symptoms increasing, and being followed by eruptions. In such cases I suspected the latent infection to have been excited by terror.”

In the instance formerly quoted from Dr. Guthrie at Petersburg, we have a notable example of this sudden seizure by a stroke. His information was derived from the physician-general of the Russian army. This gentleman assured him, that “he had seen men, in apparent good health, instantaneously drop down, as if shot by a musket ball, by the sudden action of the pestiferous miasma, and upon duty again in 24 hours, perfectly recovered by the operation of a strong vomit.” Whether or not these men felt any stroke at the instant of their falling we are not told: possibly it might be only a syncope very common in the plague, which took place at the very first invasion. Russel informs us, that “the sudden loss of strength, and disturbance of the functions attributed to the brain and heart, are reckoned, in a particular manner, symptoms of the plague. In their highest degree they distinguish the most fatal forms of the disease; and, under different modifications, adhere to all its varieties. . . . The early appearance of faintness was very remarkable in the plague,” &c.

Thus we see that the plague attacks without fever in two different modes; one, by attacking and destroying the solid parts of the body, the other, without any disorganization of the body, attacking the vital principle itself, or rather the blood, from which this principle is derived, so that a temporary suspension of all the functions ensues. The analogy between the cause of pestilence and those visible substances called poisons, is very remarkable in some things, though in others it totally fails. In the Medical Repository[102] we have a dissertation upon this analogy by Dr. Edward Miller. He observes, that this analogy has been generally overlooked, chiefly on account of the invisible nature of the aerial poison, and the suddenness of death from poisons, more frequently than from pestilential diseases. This he accounts for from the largeness of the dose of poisons compared with that of contagion; “but (says he) by diminishing the quantity to an appropriate amount, these noxious substances (the poisons) may be made to exhibit the course, duration, and nearly all the phenomena, of what is called a malignant fever. But, above all, the attention of physicians has been diverted from this analogy between miasmata and poisons, by the febrile part of the character which generally belongs to pestilential diseases, and which, in common apprehension, is constantly connected with them. Yet these diseases are by no means universally accompanied with what is strictly called fever. There is often a degree of virulence in the Asiatic plague, in the yellow fever, and in all the other forms of pestilential and malignant diseases, which altogether transcends the process of fever, and extinguishes life in a more summary manner. In the worst cases both of poison and pestilence, the febrile part of the symptoms excites little attention.”

Our author does not say in what this virulence consists. In the cases of those who die with the tokens upon them, the cause is plainly within the body; the destroying power acting with greatest efficacy below the skin in the soft substance of the flesh. Where the patient is suddenly seized in the manner described by Dr. Guthrie, the cause seems to be something foreign to the body suddenly inhaled, the effects being similar to those of fixed air when drawn in by the breath, and of consequence easily expelled by a vigorous action of the powers of the system. Guthrie observes, that, in such cases, it seems “as if the contagious matter existed in a very loose state in the first passages at the beginning of the disease.”

In the production of those tokens mentioned by Dr. Hodges, we know that there must have existed in the body a certain cause capable of totally destroying the parts, and reducing them to an hard eschar, similar to that produced by fire or by a caustic. As we are unacquainted with any thing capable of producing this effect but fire, we can attribute the origin of these tokens to nothing else but the emission of the latent heat of both the solids and fluids which compose these parts, and their consequent transmutation into an hard, and as it were charred, substance. That such an emission of latent heat does in some cases take place is evident from the production of a great quantity of sensible heat when certain substances are mixed together. Thus, upon mixing together oil of vitriol, oil of turpentine and strong spirit of nitre, the whole mixture will take fire and burn violently, though two of the ingredients, viz. oil of vitriol and spirit of nitre, are by themselves incapable of being inflamed. In like manner if strong spirit of nitre be poured upon oil of cloves or sassafras, the mixture will burst out into a violent flame. Water poured upon quick lime occasions great heat, and seems in great part to be converted into a solid substance; for only a small part evaporates, and the slaked lime falls into a powder to appearance perfectly dry, and from which the moisture cannot be expelled without a very violent fire. In this case Dr. Black is of opinion that the heat comes from the water, which, as we have already seen, contains a great quantity of it in a latent state. But, according to his experiments, the emission of 135 degrees of heat is sufficient to reduce water to a state of solidity; and the heat of lime when slaking is so much superior to this, that ships have frequently been set on fire by it. We must therefore either say that water in certain circumstances can part with much more than 135 degrees, or that the lime itself emits part of the heat it contains. This last indeed seems to be the more probable supposition of the two; for though fluids contain more heat in proportion to their bulk than solid bodies, we have no reason to suppose that the latter contain none at all: on the contrary the experiments formerly mentioned, especially those made by Count Rumford, show that they are furnished with an almost unlimited quantity.

The cause of the most violent kind of plague then we must suppose to be something received into the body, which in a certain time, probably sooner or later according to the strength of the contagion, disposes to an irregular emission of its heat, which coming by a kind of explosions, or, as Dr. Hodges calls them, blasts, produce those eschars which have been called tokens, and seem to be no other than partial combustions, by which the parts affected are reduced to a state of charcoal, or nearly so.

In assigning this cause for the most deadly kind of plague, we must naturally ask the question, how can all this take place without any pain? for of those who died in this manner, many felt neither pain nor uneasiness till within a few moments of death. This can only be accounted for by the sudden and perfect destruction of the parts, which did not allow time for any sensation of pain to take place; and indeed in the application of caustic for an issue, the patient often feels but little pain. It is impossible to avoid perceiving a very strong connexion between this kind of plague and the dreadful cases of spontaneous combustion related p. [182]–186. In the case of the priest indeed the fire seems to have come from without, though even this cannot be ascertained beyond a doubt; but in those who were absolutely consumed to ashes, it seems equally probable that it may have arisen from within; and as none of the unfortunate persons seem to have made any noise or struggle, the priest alone excepted, it seems probable that the first attack had deprived them of all sensation, and that, notwithstanding the terrible ideas with which such extraordinary occurrences must have inspired those who saw them, the sufferers may have died without feeling any pain. The priest seems to have felt nothing after the first stroke.

Should this cause be admitted (indeed whether it is admitted or not) we see that it is in vain to attempt to solve the phenomena of pestilence by the doctrine of stimuli, excitement or debility. There is no degree of stimulus, fire exepted, which can convert part of the body into an hard eschar, neither can it be done by any degree of debility or exhaustion. Besides, the irregular manner in which these eschars are scattered up and down, shows that the cause has not acted from a regular diffusion all over the body, but in a number of insulated spots, between which the connexion can by no means be traced. In all pestilential eruptions indeed the action of fire seems to be very perceptible. Gotwald mentions his having observed in two patients what he calls papulæ ardentes “burning pimples,” which Dr. Russel supposes to be a modification of carbuncular pustules. Gotwald calls them also fire-bladders, and says that they were as broad as a shilling, of an irregular shape, and the skin seemed as if shrivelled with fire. The carbuncle itself approaches much to the nature of the eschar, and is attended with violent heat in the adjacent parts. Gotwald, who gives an account of the plague at Dantzic, distinguishes the carbuncle into four kinds, (to be afterwards described.) Of these he says in general, that they all burn very violently at first, &c.

From all these accounts it seems plain, that in the plague there are partial discharges of heat, from some cause, upon various parts of the body; and that, in many instances, this heat destroys the texture of the parts entirely. When this is done instantaneosly the patient feels no pain, but if more gradually, the pain is excessive, as in the case of buboes and carbuncles; which the Journalist of the plague year in London informs us were attended with such horrid pain as to make the patients cry out in a lamentable manner. This extraordinary heat must either come from without or within, and we have all the reason in the world to believe that it comes from within. Mr. Hunter, in his Treatise on the Blood, informs us that in a local inflammation there is always an increase of heat in the inflamed part. Should this heat arise, as it probably does, from an emission of part of the latent heat, we may conclude, that such a quantity might be emitted, as entirely to change the texture of the parts. Thus mortifications or destructions of those parts may ensue, of all kinds, from the mild pus to the pestilential eschar.

In the effects of pestilential contagion we observe, if not a superiority, at least a different mode of action from what takes place in poisons. All these seem to act by dissolving the blood, or infecting it in such a manner that it supplies no sufficient quantity of animal spirits; of consequence, the creature soon faints and dies. In the plague, the blood does not appear to be much affected, nevertheless it emits, in various places, certain explosions which convert the parts into an eschar. Poisons always seem to produce the petechiæ or purple spots which sometimes appear in the plague. In Dr. Miller’s Treatise, already quoted, we find, among the symptoms occasioned by arsenic, “red or dark spots appearing on the skin, and rapid putrefaction, which renders speedy interment necessary.” Herein it differs from the plague, for the bodies of such as die of that distemper are not more liable to speedy putrefaction than others. Of the vegetable poisons he also observes, that, “after death, sometimes before, livid spots are observed on the body, the appearance of the blood is dark and dissolved, and putrefaction speedily takes place.” Of animal poisons—“The bite of the poisonous serpents is generally followed by tumour, and livid colour of the part bitten, extravasation of dark coloured blood into the adjacent cellular membrane, nausea and vomiting, sudden prostration of strength, paralysis of the limbs, convulsions, yellowness of the skin, hæmorrhages, &c. Livid appearances of the body, a dark coloured and dissolved state of the blood, and a rapid putrefaction, are observed after death.”

From all these accounts, however, it is plain, that, whatever may be the analogy between the action of poisons and malignant fevers, they do not in any manner operate like the contagion of the true pestilence. Of this the constant effect is to produce buboes, carbuncles, and other eruptions, resembling much more the effects of fire than any thing else; or, if the patient is cut off without the appearance of these, similar effects are observed on the internal and vital parts. Dr. Miller’s conclusion seems therefore liable to exception; in which he says, “that only the lighter cases of pestilence are unlike the effects of poison, but that, in proportion to the degree of malignity, the resemblance grows stronger.” It doth not appear that any poison hath produced one of the characteristic symptoms of the true plague, or any thing but what is common to animals dying of various diseases, the red spots on the skin only excepted.

In the eighth volume of the Philosophical Transactions abridged by Martyn, we have an account of a number of experiments by M. Deidier and others, made upon dogs into whose veins he injected, or poured into wounds made in the miserable animals, the bile of people dead of the plague at Marseilles. “The consequence was, that they became melancholy, drowsy, and without caring to eat. All of them died in three or four days, with the essential marks of the true plague, declared by buboes, carbuncles, and gangrenous inflammations in the viscera, in the same manner as in the human carcases from whence the bile was taken.”

The poisonous bile affected the creatures differently according to the vicinity of the place of injection to the heart. In the jugular vein it killed them in twenty-four hours, injected in the quantity of a drachm to two ounces of water. In this short time were brought on gangrenous inflammations, the heart was stuffed with thick and black blood, the liver was swelled, and the gall-bladder full of green bile. This shows a very essential difference between the action of the pestilential poison and that of others; the former, in some parts of the body at least, coagulates the blood; the latter, in all parts, dissolves it.

In the crural vein (the vein of the leg) the effects were less violent. In about an hour they became heavy. In the former case they instantly became drowsy. In the second experiment they contracted such a loathing for food, that they would neither eat nor drink any thing after the injection was made. On the third day there appeared considerable tumours under the axilla (the fore leg I suppose) and on their thighs, about three inches from the wound. The wound itself turned to a gangrene, and the creatures died usually on the fourth day.

In another experiment the animal had convulsive motions all over immediately after the injection, followed by a lethargy. Next day a carbuncle appeared on the great pectoral muscle on the right side. On the third, a bubo appeared on the thigh, and the same day the dog died. From the time of the injection he had neither eat nor drank. On dissection the fore part of the breast under the teguments was found entirely gangrened, the inward parts and viscera full of black clotted blood, the outward surface of the lungs was all purple, the heart was swelled as big again as usual, and the four cavities were full of black clotted blood. The bile of this dog, injected into the crural vein of another, produced similar symptoms, only the latter eat a little boiled meat, which he vomited up again in two hours. He died the third day, with the same symptoms of the plague as the others.

The bile of people who died of ordinary malignant fevers was much less powerful. A quantity (not mentioned how much, but probably a drachm) mixed with four ounces of warm water, was partly injected into the jugular vein of a dog, and a compress soaked in the rest of the liquor applied to the wound. He appeared heavy and sleepy, and would neither eat nor drink till the third day, when he did both willingly. On the fourth day the compress fell off, the wound was found to be diminished one half, and healed by degrees, the dog recovering perfectly. In another experiment with the bile of a patient who had died of a malignant fever, the dog not only had about a drachm of it put into a wound in his thigh, but was made to swallow some of it; notwithstanding which he was not seized with any distemper, and the wound healed in fifteen days. This bile was as black as ink, in great quantity, and very thick. In the other subjects it was of a deep green. In another experiment, with the same bile applied on a compress, the dog likewise escaped without any apparent disorder; but in a third, the animal died in twenty-three hours, though at first he had shown no sign of being affected, only that he seemed to be thirsty, and drank with greediness. On opening him his heart was found still to beat with violence, and, after the beating ceased, no blood was to be found in it, either in the auricles or ventricles. “This liquor, crowded together in the great vessels, appeared of a lively red, and very fluid, without any of those concretions that we constantly observed in those who died of the plague. Here appeared neither external nor internal marks of the plague.” The bile of a person who had died of an erysipelas, injected into the crural vein of a dog, produced no bad effect. A dog was killed by half a drachm of Hungarian or blue vitriol injected into the jugular vein. He died in universal convulsions: the heart was full of grumous blood, reduced to a kind of thick pap, but without any clots. The bile, applied to two wounds in another dog, produced no bad effect.

From other experiments it appeared that even the pestilential poison itself, taken into the stomach of dogs, did not produce any deleterious effects. “A dog of the Hospital of the Mail in Marseilles, who followed the surgeons when they went to dress the sick, used greedily to swallow the corrupted glands, and the dressings charged with pus which they used to take off the plague sores: he licked up the blood that he found spilt on the ground in the infirmary; and this he did for three months, being always gay, brisk, well, full of play, and familiar with all comers.” The health and briskness of this unfortunate dog proved his ruin, by making him the subject of philosophical experiment. A drachm of the pestiferous bile injected into the crural vein, killed him in four days. He had a considerable hæmorrhage from the wound the night before he died, and he had also a disagreeable smell both while living and after he was dead. Two other dogs, which had swallowed a quantity of pestiferous bile, became heavy and melancholy, refused their food, and showed other signs of disorder; but all these went off in a short time, and no signs of the distemper appeared.

These experiments induced M. Deidier to suppose that the contagion of the plague lay only in the bile; but the following experiment shows that the blood was equally infected, and capable of communicating the disease, and that of the most malignant species. It was made by M. Couzier, physician to the infirmary at Alais, and in the Philosophical Transactions we have the following account: “I took a quantity of blood from a person dead of the plague, and mixed it with warm water, which mixture I attempted to inject into the crural vein of a dog, but the end of the syringe being too large to enter the vein, the experiment did not succeed. This made me resolve to try to lay some of the same infected blood upon the wound. This I accordingly did, and covered it with a dressing, which the dog got off in the night. I found the next morning that the dog had licked the wound, and that he refused his food. Towards night he began to bemoan himself, and gave signs of an approaching death. The next morning I found him dead, the wound being considerably swelled and gangrened, and the edges round the swelling were likewise gangrened.

“Upon opening the body, we found the liver something larger than usual, with spots of a livid purple, as in the bodies of persons dead of the plague. In the stomach was found a quantity of black coagulated blood, of the size of a hen’s egg. This in all likelihood was what he had swallowed upon licking the wound. The heart was very large, with a black grumous blood in the ventricles, and the auricles were turned blackish and gangrenous.”

This last experiment naturally brings to remembrance those of Dr. Home at Edinburgh, in which he inoculated the measles by means of the blood of patients ill of that disorder. From the accounts he has given in his treatise entitled Medical Facts and Observations, we can have little doubt that his experiments succeeded, however others may have failed. One thing, however, is very obvious, viz. that if we mean to communicate a disease by means of the blood, we must use a much greater quantity than if we make the experiment with the matter of an abscess. The case of contagious diseases seems to be the same as in fermenting liquors. With a small quantity of yeast we can easily induce fermentation in any proper liquor, but, if we skim off the yeast, and use only the pure fermenting liquor, we must use a much greater quantity; and to inattention to this circumstance we may with probability ascribe the difficulty which Dr. Home himself met with in introducing the disease, and the total want of success in others. In M. Couzier’s experiment a considerable quantity must have been used, as he says that in the dog’s stomach it equalled the size of an hen’s egg. A much smaller quantity of matter taken from a pestilential abscess is capable of producing the disease in a human body, as is evident from the case formerly quoted of that gentleman who inoculated himself for the plague, and of which Dr. Guthrie gives the following account: “This was Mathias Degio, one of the surgeons of the hospital at Bucharest, a building appropriated to the cure of the plague in the Russian army. He, perceiving the gentlemen of his profession condemned in a manner to death, if punctual in the discharge of their duty [103] had the resolution to inoculate himself for the plague, in the full confidence of its efficacy, and ever afterwards found himself invulnerable, whilst his companions around him were falling victims to its fury. He produced the disease by inserting, with the point of a lancet, under the epidermis of his arm, matter from a pestiferous abscess, and followed the cold regimen observed in the small-pox, as he had imitated its mode of inoculation. On the fourth day of the puncture the fever declared itself, and he, being perfectly devoid of fear, got through the disease without feeling more inconvenience than if it had been that which he imitated. He drank freely of cold water, with vinegar, or a little wine, and kept generally out of doors. This beverage was the only thing that had the appearance of medicine,” &c.

From a careful attention to all these histories, it is plain that the plague is naturally an eruptive disease, as, in all the animals in which it was artificially brought on, eruptions took place, provided the life of the creature was sufficiently prolonged to allow them to come out. Dr. Russel says, that, from his diary, he noted down the cases of two thousand seven hundred patients, all of whom had eruptions of one kind or other. In this it agrees with the small-pox, which Dr. Mead justly considers as an inferior kind of plague. In the latter, however, the eruptions seem to resemble those called by Dr. Hodges the tokens, only that the cause which produces them is less violent in its nature; but why the eruptions of the small-pox should be in distinct pustules, and not one continued boil all over the body, is undoubtedly inexplicable on any theory whatever. The same is true of the plague. No man can explain why the tokens, for instance, instead of being collected into one great eschar, are dispersed into small distinct pieces; or why, instead of buboes in the groin and armpit, or instead of carbuncles in different parts of the body, there should not be a single one equivalent in bulk and power to them all. This appears similar to the phenomena of rain, hail or snow, which fall in distinct drops, fluid or congealed, or in flakes, instead of being equally diffused all over the spot on which they fall. In the latter case we say that the phenomenon is occasioned by electricity: we may say the same, if we please, of the small-pox and plague, with equal emolument.

From the accounts we have just now quoted, it appears that there is between malignant fevers and the true pestilence a very essential difference; the latter tending to thicken the blood, the former to make it thinner. In this respect therefore the poisons seem to resemble malignant fevers very considerably; for M. Fontana observed that by mixing animal poisons with blood drawn from a vein, it was prevented from coagulating. In the instance above related where a dog died in consequence of bile injected into his veins from one who died of a malignant fever, the blood was found extremely fluid. In some who died of the hospital fever, Sir John Pringle informs us, that suppurations had taken place in the brain; but in the true plague the tendency to mortification always prevailed above every thing.

Lastly, that the plague proceeds from too great a quantity of heat, either emitted from the body itself, or some how introduced into it, seems to be pretty plain from the effect it has of augmenting the venereal appetite to an almost inconceivable degree. This was taken notice of in the plague of Marseilles, and indeed in many others. Russel quotes two remarkable passages to this purpose; one in a plague at Genoa, the other in Messina. “Amidst so many dreadful fears and terrors, amid so many fetid and putrefying bodies, amid the shrieks, the sighs and the groans of the sick, what would you have expected? That the people, struck with dread and horror, remained sad, modest and quiet. You are mistaken. They sung, played on instruments, danced, intrigued, and Genoa never was seen so shameless, debauched, and disorderly. I have said before, that God in this plague gathered in a harvest for heaven; but it seemed to be also a vintage for the lascivious of of the earth. If not so, how came so many marriages to be celebrated in the Lazaretto of Consolation, and that so many women, without shedding a tear for the death of their husbands, immediately entered into new engagements? One day, in particular, five marriages were performed, four of the bridegrooms being buriers of the dead, and dressing themselves and their brides in clothes stripped off from the bodies of the deceased.” On the plague of Medina he quotes the following extract of a letter written by a gentleman who resided in that city during the plague in 1743. “It has always been observed, that, after every plague, those who recover are addicted in an extraordinary degree to lewdness and incontinence, which was surprisingly visible at Messina, and carried to such a degree of frenzy and bestiality, that many were known to violate the bodies of dead virgins!”

That an extraordinary propensity to venery may be produced by introducing into the body a quantity of heat, admits now of a kind of demonstration from a fact mentioned by M. le Roy concerning phosphorus.[104] This substance is exceedingly apt to take fire on the application of a small degree of heat, and even by slight friction. It is now introduced into the materia medica, and is found to be a very powerful medicine, though dangerous on account of its inflammability, the heat and air contained in the human stomach being sometimes sufficient to set it on fire. The taking such a substance into the body therefore seems not much different from taking actual fire into it; and indeed M. le Roy mentions the case of a woman who had taken only a single grain, and who he says had been recovered, by it, from a putrid fever, but died suddenly from some imprudence. In this woman the whole substance of the body was found luminous upon dissection, and the hands of the operator continued luminous even after being washed. M. le Roy, having taken three grains of this fiery substance, found himself extremely incommoded by it for some hours, and was obliged to drink great quantities of very cold water. Next day he found his muscular powers amazingly increased, and had an almost insupportable venereal irritation. This we see was the consequence of throwing into the body a quantity of heat from without; but if the body itself emits that heat which it invisibly contains, the effects must be the same as though an extraneous quantity had been thrown into it. Neither are we to imagine that the quantity of heat contained in our bodies is small or inconsiderable; for we have already seen that heat consists in the efflux from any substance, of an invisible and most subtile fluid, in all directions. When this flux is gentle, the heat is moderate, but in proportion to the activity of the discharge, the temperature becomes hotter and hotter, and if very violent, the cohesion of the parts is dissolved entirely, and the substance is said to be on fire. There is required therefore only some cause to begin the emission of this fluid; for as soon as this begins, the immense quantity with which we are surrounded, will supply more in abundance,[105] and continue so to do, as long as the original cause subsists, or until the substance can no longer bear the power which operates upon it.

From this view of the causes of the plague, and from the facts which have been laid down concerning it, we cannot help perceiving a very strong similarity between the plagues mentioned in the Old Testament and those which still exist in the world. In one of the passages formerly quoted it is called an inflammation, an extreme burning; and from the testimonies of different authors above quoted, it is plain that the disease still deserves the name bestowed upon it in the sacred writings. From the account given of its proximate cause, it is plain that plagues of all degrees of intensity may take place, from absolute accension of the body, and its reduction to ashes, to the mildest state of the disease, in which the patient is not confined to his bed; and all this from the single principle of emission of heat from the body itself. It likewise appears that there may be either in the body itself, or in the element which surrounds it, such a constitution as will dispose that element which is the natural and immediate preserver of our life, suddenly to attack and destroy it, of which the case of the Italian priest is a most remarkable instance. In other cases, such as the Italian lady, and the woman at Coventry, the body itself seems to have given out its heat, though this could not be done without a concurrence of the surrounding ethereal fluid. In a stage still lower, the body is partially consumed, or rather partly charred into a kind of cinder, as where the tokens are produced; and when the cause acts with still less violence, a fever is produced. In the Old Testament we find these different kinds of plagues very distinctly mentioned. In some cases the offenders died by actual fire, which either struck them from without, or was kindled within their bodies. In others, they seem to have died by that very deadly kind of plague of which we have already said so much, which kills in a few hours. This was probably the plague which destroyed the army of Sennacherib, and this in the tenth chapter of Isaiah is by some thought to have been prophesied of under the title of a burning like the burning of a fire.

Of these things I the rather take notice, as I perceive, in a late oration, not only the doctrine of the plague being propagated by contagion severely ridiculed, but the scripture itself treated in a most indecent and scandalous manner. “In the earliest ages of the world (says he) when ignorance and superstition led men to attribute all extraordinary phenomena to the direct agency of supernatural beings, pestilence was supposed to be immediately imported from heaven. This is the opinion which appears to have prevailed among the ancient Hebrews, and may be ranked at the head of the catalogue of absurdities on this subject. The dominion of prejudice over the minds of that ignorant and obstinate people appears in this instance particularly striking. Such was the depth of their blind bigotry in favour of the healthfulness of the globe they inhabited, that they would seem to have considered it as even superior to that of the celestial regions. Hence, unwilling to believe that their favourite earth could give origin to an evil so dreadful as the pestilence, they imported the seeds of this calamity from the more unhealthful climate of heaven!!”

In this extraordinary paragraph we find the matter so much misrepresented, that every vestige of truth is swallowed up in it. The Hebrews believed that they were under the immediate inspection and government of the Deity; a doctrine which, however our author may disbelieve, he cannot disprove. But, notwithstanding this immediate inspection and government, the Deity never did bring upon them any plague but by the intervention of natural causes. The agents which he had originally created were sufficiently able to execute his purposes. The Creator never employed any power but what already existed in the world, and the power that he generally did employ was fire. This agent he directed to exert its force in such degrees as he pleased, and against whom he pleased. It is a mistake to think that miracles were immediately the effects of supernatural power. They were all accomplished by the very powers which exist in the world at this moment, only these powers were by the Creator at particular times directed to act in a manner that they would not have done had they been left to the mechanism of their own nature. When we read therefore of people being consumed by fire from the Lord, there was neither importation of fire from heaven nor any where else; the element exerted its power on these particular persons, either by lightning proceeding from the cloud which represented the Deity, or their bodies threw out the latent heat which they contained, and consumed of themselves. That in cases of this kind there was no importation supposed, is evident from an expression used about bringing water from the rock. It is not said that the water fell from the stars, or came down with the tail of a comet, but that the rock gave out the water which it previously contained. At the present day the same powers exist, and sometimes produce the same effects that they did in former times, with this difference, that now, having no intelligent agent to interfere with their natural mode of action, they exert their force indiscriminately, and as the mechanism of their nature happens to be stimulated, they destroy every thing promiscuously before them. In all this I cannot perceive the smallest absurdity, or any thing but what a reasonable man may indeed must believe, if he makes use of his reason. As to the causes which Dr. Caldwell so much insists upon, viz. filth and corruption, it is extremely probable that (while the Israelites were in the wilderness) these had no existence. By their law they were enjoined such frequent ablutions, that their bodies must always have been perfectly clean. Human excrements were not allowed to lie above ground. The offals and dung of their sacrifices were carried to a distance, and they were expressly told, that they must not allow of any uncleanness in their camp, lest God should turn away from them and abhor them. Add to all this the great heat and dryness of the desert in which they wandered, which would quickly parch up and carry off the moisture from any dead carcases or putrefying matters that might be allowed to remain notwithstanding the injunctions to the contrary. Indeed if we consider the dryness of the climate where these people were, and that they were constantly attended by a large stream of water, it is difficult to conceive any situation upon earth more healthy than that of the Jews in the wilderness. If plagues therefore came upon them, it is difficult to say how they could have happened according to the ordinary course of nature; and, if not according to this, it must have been by an alteration of it, or by miracle.

The plague, as has already mentioned, in its very severe state appears most commonly in the beginning of an epidemic season, and is neither very common nor very infectious. The most common mode in which it invades the patient is with the symptoms of a malignant fever; and of cases of this kind Dr. Russel has made up his five classes of patients, the first or deadly kind having been already described. In his second class, the next in malignity to the fatal kind, the disease made its attack with a slight shivering, succeeded by fever with giddiness, vomiting, head-ach, and sometimes looseness. In the night the fever increased, the thirst was excessive, and the patient, harassed by the vomiting, &c. passed a very unquiet night, frequently with delirium or coma. Towards morning the fever abated, the sick recovered their senses if delirium had taken place, but if coma, it continued through the day, and the remissions were less. Throughout the first day, and part of the second, the pulse was full and strong, but on the second it began to alter, and some of the characteristic signs of the disease to appear. The principal of these was a certain muddiness in the eyes, which sometimes took place even on the first day. This is by our author accounted a symptom very difficult to be described, and, though he recounts the descriptions given by several authors, none are found adequate to the real appearance. “It resembled (says he) somewhat the dull, fixed eye observable in the last stage of malignant fevers; but the dullness was different, muddiness and lustre being strangely blended together. It continued with little alteration in the remissions, and even where the patient appeared sensible and composed it did not increase in the febrile exacerbations, but the eyes acquired a redness that added wildness to the look, which abating or going off in the remissions, the muddiness remained behind. It was this which contributed chiefly in composing that confusion of countenance which I shall not attempt to describe, but which enabled me to pronounce with tolerable certainty whether the disease was or was not the plague, though not independently of other symptoms. When this muddiness disappeared or abated, it was constantly a favourable sign. After a critical sign it often disappeared suddenly, but where there was a succession of sweats, or where no visible crisis happened, its disappearance was slow and gradual.”

Along with this muddiness the patient had a peculiar confusion of countenance; the pulse quick and equal, or low and fluttering, but rarely intermittent; the external heat moderately feverish, at other times intense, with irregular flushings, with pain at the heart, or oppressions about the præcordia; burning pain at the pit of the stomach, and incessant inquietude. When to these symptoms were added a faltering in the tongue, loss of speech, while the surface of the body became cold and damp with clammy sweat, death was inevitable. In the evening of the second day all the symptoms became worse; and in the morning the patient appeared to lie quiet more from his strength being exhausted than from any change to the better. When the vomiting had ceased, however, there was frequently such a remission on the third day as gave the attendants great hopes of a favourable event; but these hopes were always fallacious and of short duration. Sometimes where vomiting, looseness or hæmorrhage had preceded, the patient died on the third day: at any rate, none of this class recovered, whether the disease was left to itself, or treated with medicine. The appearance of buboes was of no consequence, for they never came to maturity, and the little advances they made neither accelerated nor retarded the termination of the disease, which happened sometimes on the third, but more frequently on the fifth or sixth day.

The third class of patients were equally unfortunate with the other two. “The difference between the second and third consisted in the absence of vomiting at the beginning, the later accession of coma and other bad symptoms, and a slight tendency to perspiration, which very rarely occurred in the second. . . . From the second or third night the course of symptoms in both classes varied very little, and the termination of the disease was in both the same: it may be added they reigned together through all the periods of the pestilential season, but were most prevalent in its augment; for at its height, and in its decline, they gave place to varieties of the disease less destructive.”

The fourth class was the most numerous of all. Its distinctive marks were, “the continuance of the inflammatory or febrile symptoms with less interruption than in the other, a pulse more constantly sustained, or soon recovering itself when hurried in the exacerbations; the length and vigour of the exacerbations decreasing in the advance of the disease; and, above all, the prevalent tendency to a favourable discharge by the skin, with the critical sweats on the 3d, 5th, or subsequent days. . . . Vomiting was a concomitant in about one fourth of the sick. The fever, for the most part, was very moderate the first night, very rarely accompanied with delirium, and almost never with the comatous disposition. . . . The buboes and carbuncles commonly made their appearance the first day; but it was not unusual to see a successive eruption of these in the course of the disease. . . . The morning sweat, on the third day, in some cases proved completely critical, but more commonly produced only a remission so favourable as to encourage the expectation of a more favourable crisis on the fifth; but, where the patient neither sweat on the third, nor a sensible remission took place on that day, some degree of danger was always to be apprehended. . . . After the sweat on the fifth, the subsequent exacerbations proved slighter and slighter, and the buboes for the most part advancing favourably, little or no fever was left remaining after the beginning of the second week, except perhaps symptomatic heats occasioned by the eruptions.” In this class the patients sometimes appeared only to have a slight attack, and yet at last were seized with mortal symptoms, while others who deemed to be much worse at first yet happily recovered and did well, In general the severe pestilential symptoms did not come on till a considerable time after the attack.

To the fifth class our author refers all cases of slight infection, wherein the more formidable symptoms of pestilence never concurred, and all the infected recovered. “The access here was often attended with so little apparent disorder, that the eruptions gave the first alarm; and the fever which came on afterwards was frequently so slight as not to confine the sick to the house. Others found themselves indisposed for two or three days, but were not sensible of any febrile heat whatever. But in this class the disease did not always invade thus insensibly. The febrile symptoms, especially the first three days, sometimes run pretty high; and the fever afterward, in nocturnal exacerbations particularly, run out to the end of the week or longer: but, as there was no concurrence of alarming symptoms, and the exacerbations, terminating for the most part in sweats, gradually diminished in force after the third or fourth night, it was not difficult in the worst cases to foretel the event at that period, nor necessary in others to defer the decision so long.

“All the infected had buboes or carbuncles, and very often both eruptions concurred in the same subject. Persons not confined by indisposition were often, by the inguinal buboes, prevented from walking abroad. The carbuncles constantly formed the black crust,[106] and then suppurated; the buboes in one third of the sick dispersed. The dispersion of the buboes was never observed to be attended with bad consequences, notwithstanding the general neglect of purging in the decline of the disease: indeed very few had recourse to remedies, topical applications excepted, unless perhaps a bleeding at the beginning, where the febrile symptoms ran high. This class was nearly as numerous as the fourth, but began to predominate rather later, and reigned most of all in the decline of the plague in 1762.”

The sixth class must be omitted, as containing dubious, anomalous and extraordinary cases. We shall therefore proceed to consider the accounts of the plague given by other physicians, which, without questioning the accuracy of Dr. Patrick Russel in relating what he has seen, may serve to throw some light on the subject, by relating what others have seen. Dr. Alexander Russel, in his Natural History of Aleppo, gives the following description of it. “The distemper in itself is the most lamentable to which mankind are liable. The torments of heat, thirst and pain frequently unite in some patients; an unspeakable dejection and languor in others; and even those who escape with life do not cease to suffer from painful and putrid ulcers, the painful remains of the disease. The desertion of relations, of friends, and of domestic servants, the want often of the common necessaries of life, and the difficulty of procuring medical assistance, are circumstances likewise which aggravate the miseries of the sick, and contribute greatly to augment the general horror.

“But, as no disease incident to mankind is in its nature more terrible and destructive, so none is more difficult to observe. Its symptoms are scarcely in all respects alike in any two persons, and even vary extremely in the course of an hour in the same subject. The disease, attended in the beginning with symptoms not highly alarming, often ends fatally in a few hours; while the most formidable attacks, by a sudden and unexpected alteration, sometimes terminate happily.

“The first complaints of those seized with this distemper, were, in general, a coldness or shivering; sickness; a vomiting of large quantities of porraceous bile, which often had a very offensive smell; anxiety, or an inexpressible uneasiness about the pit of the stomach; pain in the back or loins; an intense head-ach; uncommon giddiness, and a sudden loss of strength. Some were sensible of a sharp shooting pain darting at intervals into the parotid, axillary or inguinal glands. To these symptoms succeeded a violent fever; in which, while the sick complained of extreme inward heat, their skin, externally to the touch felt little hotter than usual. Sometimes this heat became general and intense; at other times particular parts only were affected; but it seldom continued long in the same degree, having several unequal remissions and exacerbations in a day. In these exacerbations the face became florid, but would often from a deep scarlet change to a livid colour, like that of a person almost strangled, and, again suddenly changing, it would assume a cadaverous paleness. The eyes, soon losing their natural lustre, acquired a kind of muddiness; and the countenance of most of the sick was ghastly and confused beyond description. The pulse the beginning was somewhat quicker and lower, but in other respects varied little from the natural state. Within a few hours it commonly increased in quickness and strength, but seldom remained the some for an hour, nay scarcely many minutes together; incessantly varying, both as to strength and quickness, and without any manifest correspondence with the other febrile symptoms.

“In such as complained of pains darting either into the parotids, the arm-pits, or the groins, a small hard, deep-seated tumour, with external discoloration of the skin, was discovered by the touch in the part, and these were the incipient pestilential buboes.

“The appearances now described were those of the distemper on the first day, till evening, when the sick always suffered a severe exacerbation, in which the heat both internal and external became excessive; and, as they generally were by that time delirious, it was often with difficulty that they would be kept within doors; they were greatly disposed to talk, but faltered so in their speech, that what they said was hardly intelligible, the tongue having shared with the other organs in the general debility. The exacerbation lasted the most part of the night; but the heat, delirium, and inquietude abated towards morning, and a manifest remission took place. Some recovered their senses entirely, some partially, and then complained of intense head-ach, or of pains from the buboes; it was usual in this interval also that those who had carbuncles began to complain of burning pain in those fiery eruptions. The morning remission was commonly of very short duration; the rigours, anxiety and delirium soon returning more violent than before, attended with a strong and frequent subsultus tendinum. These febrile symptoms did not increase regularly as the day advanced; but went away and returned at intervals leaving short but alarming intermissions; for each exacerbation surpassed that which preceded it either in violence or duration. In the evening the pulse could hardly be counted, by reason of its depression and quickness; the patient became comatose, and the respiration was quick, laborious, and interrupted. The buboes which, some hours before, seemed manifestly to advance, often subsided, and sometimes almost entirely disappeared; the carbuncles, mortifying at the top, resembled a great eschar made by a caustic: and at this period also livid or black spots, of various dimensions, often were found scattered universally on the body.

“Under these circumstances, dreadful as they seemed, some hope of recovery still remained; for, though many of the sick died on the third day, several had a favourable crisis on that day, by a profuse sweat; some struggled to the fifth day, a few to the seventh, and, here and there one, even to the eleventh; before any critical alteration took place. Where a copious sweat happened on the third day, if it did not prove perfectly critical, it at least always considerably abated the fever; which, in that case, was generally totally removed by a second, though less profuse sweat, on the fifth: and then besides weakness the chief remains of the disease consisted in the pain of the eruptions.

“Nothing could be predicted with respect to the event of the disease from the manner of its invasion; those who had the most favourable escape having been often in the beginning attacked with as alarming symptoms as others were who died in a few hours. Sometimes the febrile paroxysm, which had set in with such formidable violence, dissolved in a few hours, and left the patient languid indeed, and weak in an extreme degree, but free from other complaints except the pain arising from the bubo, which from that period increasing in size, and advancing favourably to maturation, was, in many cases, ready to open in twelve or fifteen days: the patient all the while, except the first day, walking about as usual. Great numbers happily escaped, not only in the manner just described, but likewise where the buboes never advanced; for these tumours, so far from coming always to maturation in such as recovered, very often discussed without any bad consequence. Carbuncles often began to digest before the termination of the fever in a critical sweat.

“All the infected had buboes, except such as expired suddenly, or survived the first attack a few hours only. Instances of this dreadful kind were more particularly observed in March 1743. The sick were seized in the usual manner; but the head-ach, vomiting, and pain about the præcordia, increasing every moment, proved suddenly mortal, or terminated within a few hours in fatal convulsions.” Dr. Patrick Russel observes, that such instances of sudden death were very rare in the plague of 1760, 1761 and 1762; and in these they happened only in the winter, or early in the spring. In such sudden deaths few had any appearance of buboes; but in general the armpits and groins, or the inside of the arms and thighs, became livid or black, and the rest of the body was covered with confluent petechiæ, livid pustules being here and there interspersed: but all these appearances were more especially observed after death.

In the plague of 1760, vibices as well as livid and black spots were frequently found on the corpse, but not constantly. They were always suspicious in conjunction with other circumstances, but their absence was no proof, though frequently urged as such, that the distemper was not the plague. The vibices sometimes appeared several hours before death, but the livid spots seldom or never.

The tongue in some was quite moist, and continued to be like that of a healthy person throughout the disease; in others, white at first, then yellow; at last black, and covered with a dry, foul scurf or fur. The thirst was generally very great, but never constant; returning at regular intervals, and never appearing to correspond with the danger of the fever. Sometimes it was so little that the patient could not be prevailed upon to drink a sufficient quantity. The appearance of the urine was equally variable, and afforded no certain prognostic; being seldom alike in any two patients in the same stage of the distemper, and varying in the same patient every day. The vomiting commonly ceased after a few hours, excepting where the sick were induced by thirst to load their stomach, in which case it always returned. Sometimes the patients were costive, in others a diarrhœa took place, but in most the discharges were natural. No critical solution by urine or stool seemed ever to take place. A few cases of hæmorrhages from the nose and uterus were observed; and if they happened after the second day, were soon followed by a plentiful sweat, which commonly proved critical; “a circumstance different from what has been usually observed in the plague at other places.

“From the preceding account of the plague it will readily be conceived that nothing can be more difficult than to form any judgment or prognostic of the event of the disease; in which, as it is justly remarked by Morellus, our senses and our reason deceive us, the aphorisms of Hippocrates are erroneous, and even Hippocrates (as I am inclined to think) might have erred in his judgment.”

Innumerable other histories of the distemper might be given, but the following, it is hoped, will be sufficient, along with what has been already detailed, to show that the plague in former ages was the same as at this day. In the terrible plague which broke out in the time of Justinian, the distemper sometimes began with delirium, and the patient instantly despaired of life; but more generally people were surprised by the sudden coming on of a slight fever; so slight that no danger was apprehended either from the state of the pulse or colour of the body. This, however, was quickly followed, sometimes even on the same day, sometimes on the second or third, by buboes or parotids (swellings behind the ear) which when opened were found to contain a black coal, or eschar, of the size of a lentil. If these swellings suppurated kindly, the patient recovered, but if not, a mortification ensued, and death was the consequence, commonly on the fifth day. Black pustules or carbuncles, covering the body, were signs of immediate death, as was likewise a vomiting of blood in weak constitutions; for this terminated in a mortification of the bowels. Pregnant women generally perished, but women were less susceptible of the infection than men; and young persons were in more danger than old. Many, who recovered, lost the use of their speech, and such were not secure from a relapse.

In the last plague at Moscow, the symptoms were various, according to the persons, constitution and the weather; in general, head-ach, giddiness, shivering, loss of strength, slight fever, sickness and vomiting, redness of the eyes, white and foul tongue, with a dejected countenance, buboes and carbuncles appearing on the second or third day, but seldom on the fourth. The buboes were seated chiefly in the glandular parts, the armpits and groin, but sometimes made their appearance in the neck, cheeks, &c. Sometimes these suppurated perfectly, and then they proved beneficial, but not otherwise. Sometimes they suddenly disappeared, after having attained the size of walnuts; and this retrocession was always supposed to be a sign of approaching death. Sometimes they neither showed any sign of inflammation nor were painful, and in such cases afforded no relief. Similar swellings sometimes occured in the parotid glands, but they were never equally beneficial with the buboes. Carbuncles were gangrenous spots on the skin, resembling a burn, with black, livid or red vesicles, bordered with an inflammatory ring, and soon terminating in a hard, black eschar. The anthrax is more prominent, penetrating deeper into the adipose membrane, and attended with more pain and inflammation. The disease was likewise attended with petechiæ similar to those in putrid fevers, but larger; also with vibices, which resembled the mark of a whip, and were considered, as well as the petechiæ, as mortal signs. No distinct account of the pulse could be given; as, after the disease became general, physicians did not choose to feel the pulses of their patients but through a glove or tobacco-leaf. Worms called teretes were frequently discharged both upwards and downwards. Women with child generally suffered abortion, and were carried off by an uterine hæmorrhage.[107]

According to Sydenham, the plague begins with chilliness and shivering, like the fit of an intermittent, succeeded in a little time by violent vomiting and oppression at the breast, accompanied with its common symptoms. These continue till the disease proves mortal, or the kindly eruption of a bubo or parotis discharges the morbific matter. Sometimes, though rarely, the disease is not preceded by any fever; the purple spots, which denote immediate death, coming out even while persons are abroad about their business. But this hardly ever happens but in the beginning of a very fatal plague, and never while it is on the decline, or in those years in which it is not epidemic. Sometimes swellings appear without having been preceded either by a fever or any other considerable symptom; but he conceives that some slight and obscure shivering always precedes the seizure.

Mariti, in his travels through Cyprus, &c. says that the plague of 1760 began with loss of appetite, pain in the shoulders, head-ach extremely violent, delirium, vomiting, with a most excruciating pain in that part where the tumour by which the plague is characterised, is about to break forth. Death often took place on the third day, and very few lived beyond the thirteenth.

The Abbe’s definition of what he calls the plague, and which seems to be the pestilential bubo of the physicians, is somewhat singular. “The plague (says he) is an oblong tumour, shaped like a pumpkin, which is at first of a flesh colour; but it gradually becomes red, and at length blueish; and this is a sign that the disease is incurable. If it continues red, and a little after inclines to yellow, it is a sign that a suppuration will take place: the swelling is then opened, and the patient is sometimes cured.”

According to our author, the symptoms of the plague do not appear till fifteen days after the infection is received; and this is the reason of a law which subjects to a proof of twenty days every person suspected of being diseased. In this plague it was observed that people of the soundest constitutions were the most subject to it, and the least capable of resisting it. On the other hand, it appeared to spare weak and delicate persons, whose cure, in case of an attack, was much less difficult. A greater number of Moors than of any other nation were attacked by it; and when once they were seized, their case was absolutely desperate. Those who had recovered from the disease were less liable to a second attack, but were not absolutely safe. “I have known some (says our author) who have been ill seven times, and have died of it at last.”

Dr. McBride informs us that in the plague which raged at Marseilles and the adjacent places in 1720, people on their first seizure seemed as if intoxicated with drink; they lost the power of their limbs entirely, and became so dejected that they gave themselves over to despair from the very first attack. Along with the bilious vomitings and purgings which generally took place on the second day, quantities of small worms like ascarides were thrown off. The more plentiful these evacuations were, the more salutary; for those who vomited and purged but little sunk down, oppressed with the disease, and died before the fourth day, covered with livid blotches and petechiæ; those who had the largest evacuations had also the most plentiful eruptions of buboes and parotid abscesses. When these appeared, the patients rose, walked about, and became remarkably hungry; the heat and thirst subsided, but the face continued pale and languid, the pulse hard and frequent. On the sixth, seventh, or eighth day, if the suppuration stopped, and the humours went back, then came on oppression, difficulty of breathing, furious delirium and convulsions, which ended in death. When carbuncles, or biles, with mortified sloughs, appeared in different parts of the body, either alone or accompanied with the glandular swellings, the patients scarcely ever escaped. In great numbers of people tumours appeared without any previous febrile symptom, and, in a few cases, went off by resolution; in others they continued in a schirrous state; but it was best when the tumours came to suppuration.

These are the most remarkable symptoms of this fatal disease, which have been recorded by the physicians of greatest eminence who have written upon the subject. It remains still to give some particular description of the buboes and carbuncles, which are supposed to constitute in a particular manner the characteristic signs of the distemper. Of these the following account, given by Dr. Alexander Russel, seems to be sufficiently clear and explicit.

Only a very few, and such as died suddenly, were exempted from buboes, but only about one half had carbuncles. In the latter plagues their proportion was still smaller; but they seldom appeared earlier than in the months of April or May. In 1742 and 1743, the buboes often appeared on the first commencement of the distemper, sometimes not till twelve hours after; in a few instances not till two or three days; but in 1744 they were sometimes the first symptoms of the disease. The buboes were generally solitary, the inguinal and axillary more frequent than the parotid. “The inguinal bubo for the most part was double; that is, two distinct glands swelled in the same groin. The superior, which in shape somewhat resembled a small cucumber, lay obliquely near the large vessels of the thigh, lower than the venereal buboes are usually found, and it was that which commonly came to suppuration; the inferior was round, and in size much smaller. I once met with a case in which an axillary bubo divided in like manner into two parts, one of which got under the pectoral muscle, the other sunk deeper into the armpit: both grew painful and inflamed, but that in the armpit only suppurated.”

The bubo was at first a small hard tumour, painful but not inflamed externally. These indurated glands were deeply seated, sometimes moveable, at others more or less fixed, but always painful to the touch. Sometimes they would increase to a considerable size in a few hours, with intense pain, then suddenly subside; and these changes would take place several times in twenty-four hours. “An exacerbation of the pestilential symptoms immediately upon the decrease of the bubo, sometimes prompted me to imagine it owing to the retrocession of the tumour; but this did not happen so constantly as to make me think it was so in reality. The buboes, as far as I could learn, never advanced regularly to maturation till such time as a critical sweat had carried off the fever. In ten, twelve, or fifteen days, from the first attack, they commonly suppurated; having been all along attended with the usual symptoms of inflammatory tumours. But I have known them sometimes, nay, frequently, disappear soon after the critical sweat, and discuss completely without any detriment to the patient. At other times, though grown to a pretty large size, the tumour, about the height of the disease, would sink and mortify, without any fatal consequences; for, as soon as the crisis was complete, the mortification stopped, and the gangrened parts separating gradually, left a deep ulcer, which healed without difficulty. I met with no instance of a bubo in which fever did not either precede or follow the eruption.”

On the subject of carbuncles, Dr. Patrick Russel observes, that “there are certainly varieties in them, but perhaps these varieties have been unnecessarily multiplied, from the same eruption having been viewed in different stages of its progress; for all of them sooner or later are covered with a black eschar.” Dr. Alexander Russel describes them as follows: “The carbuncles were commonly protruded the second day of the disease; and though the muscular and tendinous parts were more especially affected, no part whatever could be said to be free of them. The carbuncle at first resembled an angry confluent pock in its inflammatory stage, but was attended with intense, burning pain, and surrounded by a circle of a deep scarlet hue, which soon became livid. By a progress very rapid, it then spread circularly, from the size of a silver penny to an inch and an half, two inches, nay, even three inches, diameter; and the supervening gangrene often penetrated deep into the substance of the parts affected. In such of the sick as recovered, the gangrene usually ceased spreading on the third day; and, a day or two after, signs of suppuration were observed at the edge of the black crust, the separation of which, advancing gradually, was completed rather in less time than that of the eschar in issues made by caustic. In cases where the patient died, I was informed (for I saw none of those cases myself) that a quantity of ichorous matter oozed from beneath the eschar, which remained itself shrivelled and hard, without any favourable signs of separation or digestion.”[108]

Dr. Alexander Russel also describes another kind of pustule, which he says appeared in a small number of the sick, but which his brother Dr. Patrick had no opportunity of observing in 1760. It had no livid or discoloured circle surrounding it, but was filled with laudable pus; and, when dry, the crust fell off, as in the distinct small-pox. This was looked upon as a favourable symptom, all who had it happening to recover.

We have now detailed, at considerable length, the symptoms of the plague as mentioned by authors of great eminence. To give a detail of all that has been said upon this subject would be impossible; neither indeed can it be thought necessary in the present treatise. Whatever may have been omitted or too slightly mentioned in this section, will naturally be considered when we come to treat of the cure. It now therefore only remains to say, whether the approach of a plague may be known by any visible signs, so that people might in some measure prepare themselves for the ensuing calamity.

Were we in possession of an accurate and authentic history of the world, this question might be very easily decided; but the uncertainty of ancient records, the mutilated state of those which we do possess, the diversity of opinions among mankind, and the unhappy disposition to misrepresent, so common in all ages, render it very difficult to say any thing upon the subject. If the theory hinted at in this section (that plagues arise from some commotion in the electric fluid) can be allowed to have any foundation in nature, then it ought to follow, that the forerunners of pestilence would be some electric phenomena; and, from a perusal of the first and second sections of this work, it will appear that such an opinion is not altogether unfounded.[109]

The appearance of immense numbers of insects has likewise been accounted a sign of approaching pestilence; but if we suppose their appearance to be a sign, we can scarce imagine their putrefaction to have been a cause, of pestilence. In the east we are informed by Dr. Russel that the inhabitants of Aleppo account the appearance of insects, and even eclipses, as presages of the plague. They suppose also that the stillness of frogs is a sign of pestilence; but the same author informs us that all these signs failed in 1760. Violent earthquakes and famines seem to be more certain signs, though even these are not always to be depended upon; it being evident from historical accounts that pestilence has sometimes preceded, and sometimes followed, earthquake and famine. Mr. Gibbon, however, ascribes to the above-mentioned causes, viz. insects, earthquakes, and even comets, the dreadful plague which took place in the reign of Justinian. At least, all these preceded it; but perhaps the insects were only meant to be accounted the cause of the plague. The cause of the insects must remain in obscurity. According to him, “In a damp but stagnating air, this African fever is generated from the putrefaction of animal substances, and especially from the swarms of locusts, not less destructive to mankind in their death than in their lives.”

This dreadful plague was preceded by comets and most violent earthquakes. A remarkable comet appeared in 536, supposed to be the great one observed by Sir Isaac Newton in 1680. This, we are told by astronomers, revolves round the sun in a period of 575 years; but the failure of astronomical predictions in the return of the expected comets of 1759 and 1789, shew the futility of such calculations. Another comet appeared in 539, and these comets were attended with an extraordinary paleness of the sun. Mr. Gibbon observes, that earthquakes, which he calls a fever of the earth, “raged with uncommon violence during the reign of Justinian. Each year is marked by the repetition of earthquakes of such character, that Constantinople has been shaken above forty days; of such extent, that the shock has been communicated to the whole surface of the globe, or at least of the Roman empire. An impulsive or vibrating motion was felt; enormous chasms were opened, huge and heavy bodies were discharged into the air, the sea alternately advanced and retreated beyond its ordinary bounds, and a mountain was torn from Liburnia, and thrown into the waves, where it protected as a mole the new harbour of Botrys in Phenicia.”

According to Dr. Sydenham the plague at London in 1665 was preceded by a very cold winter; the first continued till spring and went off suddenly towards the end of March. Peripneumonies, pleurisies, quinsies, and other inflammatory disorders, then made their appearance, along with an epidemic fever of a particular kind, which did not yield to the remedies successful in other epidemics. About the middle of the year the plague began, and increased in violence till the autumnal equinox, when it began to abate, and by the ensuing spring was entirely gone. Our author says that the plague seldom rages violently in England but once in thirty or forty years; but since his time, which is upwards of a century, no plague hath appeared. He supposes the plague and other epidemics to depend on some secret constitution of the air, but pretends not to say what that constitution is. But, besides this constitution, he is of opinion that there must be another circumstance, viz. the receiving the effluvia or seminium from an infected person. Thus he supposes that a single infected person is sufficient to poison a whole country; the general mass of atmosphere being infected by the breath of the diseased and the effluvia of the dead bodies. “Thus (says he) the way of propagating this dreadful disease by infection is rendered entirely unnecessary; for though a person be most cautiously removed from the infected, yet the air received in by breathing will of itself be sufficient to infect him, provided his juices be disposed to receive the infection. I much doubt, if the disposition of the air, though it be pestilential, is of itself able to produce the plague; but the plague being always in some place or other, it is conveyed by pestilential particles, or the coming of an infected person from some place where it rages, to an uninfected one, and is not epidemic there, unless the constitution of the air favours it. Otherwise I cannot conceive how it should happen, that, when the plague rages violently in one town in the same climate, a neighbouring one should totally escape it, by strictly forbidding all intercourse with the infected places; an instance of which we had some few years ago when the plague raged with extreme violence in most parts of Italy; and yet the Grand Duke, by his vigilance and prudence, entirely prevented its entering the borders of Tuscany.” As to the nature of the disease, when once produced, Dr. Sydenham is of opinion that it is altogether inflammatory; for which he gives the following reasons: 1. The colour of blood taken away that resembles that in pleuritic and rheumatic disorders. 2. The carbuncles resemble the mark of an actual cautery. 3. The buboes are equally disposed to inflammation with any other tumours that come to suppuration. 4. The season of the year may be adduced in proof of this; for between spring and summer, inflammatory disorders, as pleurisies, quinsies, &c. are common.

Before we put an end to this section, it may now be proper to say a few words by way of apology for the many apparent digressions from the subject which have appeared in it. In the first place, then, the work being intended for general inspection, and not merely for medical readers, it became absolutely necessary to introduce a number of things which for medical readers would have been totally superfluous. It was to be supposed that the book might come into the hands of some who had not read any thing concerning the structure of the body, who had not heard of any of the systems of medicine now prevalent, or the different doctrines they contain. It was impossible to write in an intelligible manner for such people without giving some few hints concerning all these subjects: the same consideration made it necessary to enter pretty largely into the discoveries concerning the composition of the atmosphere and various kinds of elastic fluids, concerning heat, &c. In doing this the writer was under a necessity either to adopt some of the doctrines he took notice of, or to animadvert upon them. If he has ventured freely to give his sentiments, it is not with a view to establish a theory of his own, but to direct the attention of the reader to those natural agents which seem to be at present too much overlooked, principally because they are less accessible to our senses, and of consequence less subject to experiment, than others. If therefore in this treatise it is suggested that the atmosphere acts on the human body by its internal or latent heat, and by its electricity, as well as by its other properties; if the writer is inclined to believe that these are in fact the most powerful parts of it; that we never can act without them, and that in short our life and health are in immediate dependence upon them; I say, that none of all these things are in opposition to any fact hitherto discovered, either of the medical kind or any other. On the other hand, in all ages physicians have sought for some constitution in the air, inexplicable, and perpetually unknown, to which diseases might be ascribed that could not be supposed to originate from any of its ordinary properties. To explore this constitution is as great a desideratum at the present moment as two thousand years ago; and any attempt to investigate it, or a conjecture relating to it, cannot be supposed inconsistent with any thing already discovered and ascertained. There are many things which lead us to think that electricity is very much concerned in diseases, and among the rest we must account the new discovery of Dr. Perkins’s metallic conductors a very notable proof of it. These, when first ushered into the world, were made by many a subject of ridicule; but the evidence in favour of their efficacy, both in America and in various parts of Europe, seems now to be decisive in their favour; and, if they act at all, it is almost impossible to suggest any other principle than that of electricity to which their efficacy can be owing. No doubt it is difficult to draw the line properly betwixt credulity and skepticism, but where credible testimony determines any thing to have actually happened, or where solid reasoning gives room to suppose any thing to be probable, it never can be invalidated by any argument a priori formed against the possibility of such a thing taking place.

In page [128] it is said, that M. Lavoisier, by introducing the new chemical nomenclature, “has entailed the greatest curse upon the science it ever met with.” All apology for this bold assertion is absolutely necessary, and the quotation made from Dr. Ferriar may be deemed inadequate, or perhaps misapplied. In passing this censure on the nomenclature I wrote from experience. The new nomenclature, instead of promoting my improvement in chemistry, hath had a direct contrary tendency. An instance of the inconvenience and ambiguity arising from it is given p. [135], when speaking of Dr. Girtanner’s theory. But a much more remarkable example is to be met with in the review of Dr. Monro’s Chemical Treatise, where we find him censured for the very same ambiguity taken notice of with regard to Dr. Girtanner. “He might have observed (say the reviewers) the distinction between the hydrogen and inflammable air, and between the oxygen and pure air, as well as between the azote and impure air: he has mentioned these as synonimous, whereas they are terms that express bases, or substances in a concrete state (what I have called the condensable part) and the compounds of these substances and heat, when they assume the form of gases or elastic fluids.” (Monthly Rev. for 1790, p. 26.)

That the terms invented by Lavoisier and others have not been received with perfect unanimity by the chemists of the present day, is evident from Dr. Pearson’s “Translation of the New Chemical Nomenclature,” which is not only a translation, but a vindication of it. In the course of his work he quotes the translator of the Chemical Dictionary saying, that, “from the zeal of reforming language, such a number of reformers may arise, that our ears will not be less stunned, nor our understandings less perplexed, than if we were exposed to the clamour of Babel, or the thaw of words of Sir John Mandeville.” To this Dr. Pearson replies, that there is no reason to fear any such bad consequences. “The distinguished superiority of a system produced by a De Guyton, a Lavoisier, or a Bergman, would surely supercede the work of persons of inferior ability.” It is impossible to know the persons here designated, unless the Doctor points them out. If he chooses to call himself one of them, we can have no objection. He certainly has dissented, in one article, from “the system produced by De Guyton, Lavoisier and Bergman,” and this is with regard to the word azote. This is the term announced to us as the most proper for denoting a certain kind of air. But Dr. Pearson determines nitrogen to be more proper. Even this has not given entire satisfaction, for Dr. Mitchell has adopted the word septon in preference to both azote and nitrogen. Thus, instead of the original phrase phlogisticated air, used by Dr. Priestley, we have four; for as long as the works of Dr. Priestley remain, the original term will be used by some, while with others it will be so much disused that perhaps they will not understand it when it happens to occur. Nor are corrections of this kind all that we have to fear. Professor Wiegleb, who has written a System of Chemistry in quarto, has therein changed almost all the nomenclature invented by Lavoisier. Instead of it he gives a nomenclature of his own, in which he makes very much use of the termination cratia, from a Greek word signifying strength; thus, instead of saying the acid of fluor, we are to say fluoricratia. I must confess that to me the perpetual repetition of this termination has a very ridiculous appearance; but the misfortune is, that in the case of nomenclatures we have no choice. We cannot choose one and reject another: good or bad, we must take both; and were an hundred new ones to arise, we must be condemned to learn them all. Nor is even this the worst. Wiegleb’s scholars, for instance, accustomed to the language of their teacher, will be apt to put it into their writings, perhaps without proper explanation; and thus such writings must be unintelligible both to old and new chemists: and thus it will be with as many others as choose to invent new chemical terms.

Were this a proper place for entering into a discussion of Lavoisier’s nomenclature, it might easily be shown that the terms are not more proper than those which preceded them; but no real inconvenience can arise from the propriety or impropriety of a mere name. It is the resemblance of the terms to one another, and the facility with which mistakes may be made, that gives just ground of complaint. Nor is it any just reason to accuse a person of want of judgment or carelessness because he hath mistaken these terms. We see that even Dr. Monro has not attended to every circumstance; and if a man of his experience and accuracy hath been inaccurate in this respect, what is to be expected from others? How easily may the words sulfate, sulfite, sulphuret and sulphure, be mistaken for one another, either in writing or conversation! Yet a mistake of this kind would totally pervert the meaning of the person who used it. The scripture finds fault with those who make people offenders for a word; but here we are in danger of being made offenders for a letter. In short, taking into account the inconveniences arising from this nomenclature itself, the numberless corrections and amendments (no matter whether real or imaginary) to which it may be subjected, and the number of others totally different from it which may arise, I cannot help looking upon the introduction of it into chemistry as an evil of the first magnitude; an evil which cannot be remedied by any art, but must continually become worse and worse.