“1. Dr. Odier of Geneva, in a letter to Dr. Haygarth, writes thus: ‘I believe it would not be difficult to prove that the state of the atmosphere is in no respect the cause (of the regular epidemics of that city;) for the villages and towns which surround it do not experience the same epidemic all years as Geneva, although they are situated under the same heavens, and exposed to the same vicissitudes of atmosphere.’ 2. Sydenham conjectures that some effluvia, issuing from the bowels of the earth, produce epidemics. Were this true, it might advance one step towards a solution of the difficulty by discovering a local difference in the atmosphere. But it has never yet been pretended that any such vapour was perceived. Yet every part of the earth must be capable of furnishing it; as no portion of the whole habitable globe has been discovered where the air could not propagate the small pox. . . . 3. Hence we may safely conclude, that the slight variations of the same climate, and the same season, must be altogether insignificant and nugatory. What important difference of atmosphere can be supposed to exist for weeks or months together in two neighbouring villages, or in the adjacent streets of the same town? This remark is plainly applicable to the propagation of the plague and other infectious distempers. Yet the latest and most respectable authors continue to be misled by this groundless hypothesis.”
Objections of this kind do not solve the difficulty. The excessive disparity of seasons with respect to the spreading of epidemic diseases, the long cessation of them at some times, and their sudden revival, as if with redoubled fury, at others, indicate the operation of some cause invisible to us; but whether that cause resides in the earth or in the air, cannot easily be known. As contagious matter seems to operate by being received with the air into the lungs, it would seem rather probable that the ultimate cause of epidemics resides also in the air. Dr. Haygarth complains that the vapour arising from the earth, supposed to produce epidemics, should be invisible; but the contagion of the small pox, or of any other infectious disorder, is equally so. It must, he says, be diffused all over the earth. The electric fluid is so; it issues from the earth in every part of its surface, as is demonstrated by the common experiments of electric machines; and there are the strongest reasons to believe that it issues at some times and in some places in much greater abundance than others. But enough has been said on this subject; we must now consider matters a little more obvious.
Though it is not easily seen in what manner the proportion of the ingredients which compose the atmosphere can be changed, and we are unable to discover the operation of the more subtile fluid contained in it, yet we are certain that its constitution must be different in different parts of the world. Islands, from their being surrounded on all sides by the sea, must of consequence have an atmosphere considerably different from that of the internal parts of continents, where the air always passes over large tracts of land. Hence the continent of America, being situated between the two vast oceans called the Atlantic and Pacific, must possess a constitution of atmosphere considerably different from that of the Eastern. Of consequence, the diseases of Europe and Asia, when transplanted to America, or to the American islands, will probably, sooner or later, assume a type different from that which they had in their own country. Dr. Waterhouse has taken notice of this in his letter to Dr. Haygarth, and thinks that it may hold good even in the small pox. “May not the small pox (says he) operate differently in the two countries? It has certainly had a different appearance, and required a somewhat different treatment, almost every time it has come among us. That the difference in the virulency of the small pox, observed at different periods, when epidemic here, may be attributed to a peculiar constitution of the atmosphere, no one seems to doubt; and why may not the difference, so reasonably to be expected between the atmosphere of your island and this continent, allow us to suppose that there is some difference in the facility of receiving the infection?” This is also an important consideration, and may throw some light on the cause, as well as the mode of prevention, of this disease.
Lastly, Dr. Seaman attempts to disprove the authenticity of some cases which have been brought as positive proofs of the disease having been received by infection. These belong not to us to consider; it being impossible, by reason of the invisible nature of contagion, to determine from a simple consideration of any patient’s case whether it was infectious or not. Dr. Fordyce has laid down the proper rule for judging in such cases.[179] One only of the instances brought by Dr. Seaman therefore we shall mention, and that, not because it proves any thing, but on account of its singularity. “Daniel Phœnix, city-treasurer of New York, is supposed without doubt to have taken his complaints from contagion: the corporation, some time past, having issued into circulation, for the accommodation of the inhabitants, a great number of paper penny bills, it has been concluded that he must have received contagion through the medium of some bundles of these bills, which he opened, that had been nearly worn out, to be exchanged, and which he opened and examined to ascertain their amount some days after he had received them.” The Doctor allows that he might have been infected by the bills, but ascribes it to putrid effluvia.[180]
Dr. Smith, in his letters to Dr. Buel, insists much on the vitiated state of the atmosphere, and is at some pains to describe the persons who were most subject to it. These, in 1795, were for the most part foreigners; under which denomination the Doctor comprehends those who came from other states, from the West Indies, and from Europe, or who had not been many months or years settled in the city. The number of citizens who suffered he does not suppose to have exceeded one in seven; but he remarks, that, both among foreigners and citizens, the severity of the disease fell chiefly on the poor. This mixture of different nations he accounts, and with great probability, one of the causes of the distemper. In confirmation of it he quotes Dr. Blane, on the diseases of seamen, remarking, “that it sometimes happens that a ship, with a long-established crew, shall be very healthy; yet if strangers are introduced among them, who are also healthy, sickness will be mutually produced.” The same observation is made by Dr. Rush, who, besides a general reference to the history of diseases, adds the following remarkable fact: “While the American army at Cambridge, in the year 1775, consisted only of New England-men, whose habits and manners were the same, there was scarcely any sickness among them. It was not till the troops of the eastern, southern and middle states met at New York and Ticonderoga, in the year 1776, that the typhus became universal, and spread with such peculiar mortality in the armies of the United States.”
This confirms the observation made in the former part of this treatise, when speaking of the English embassy to China. It may likewise with probability be assigned as one reason why large manufactories are generally so unhealthy. In them there always is a collection of people from many different and distant parts; and what holds good on a large scale must also do so on a smaller one. But this does not disprove the doctrine of contagion, but rather confirms it; for, if the discordant effluvia rising from healthy bodies of different constitutions can generate a disease, much more may we suppose the effluvia from sick persons capable of continuing and propagating it.
Now, let us consider the account, imperfect as it is, which we have been able to collect concerning the appearance of the yellow fever on the Western Continent. We have seen (p. [377], n.) that, at the time the plague was in England, five of the Americans were transported to that country; two of whom, after staying some time in England, were sent back, with other strangers, to America. This first colony having failed, another was sent; the Indians went to war among themselves, and the yellow fever is supposed to have made its appearance. Here a suspicion naturally arises, that a slight pestilential taint had been imported by some of these strangers, and that what would have been the true plague in Europe or Asia, by reason of the peculiar constitution of the atmosphere in the New World, there became the yellow fever. The same may be said of the original importation of it into Martinico. Sauvages expressly says it was the plague which was imported. Moseley and others deny that any such disease as the yellow fever exists in Siam; and indeed it seems at any rate to be a new disease. It seems possible that diseases may change their nature; and Dr. Ferriar has given a dissertation on the conversion of diseases. As therefore the true plague never made its appearance in America or the West Indies, it seems not unreasonable to suppose that these countries are incapable of receiving it, but that the pestilential poison, when transported to the Western Continent, may assume a different, and in many respects an opposite, nature; the two diseases being thus like the opposite poles of a magnet, scarce agreeing in any thing but the common work of destruction.
It is needless to spend time in attempting to investigate the cause of this disease appearing at different periods. That of 1793 has been the most remarkable and the most destructive; the disease having never since that time ceased its ravages. Previous to its appearance at Philadelphia that year, Dr. Rush observes, that, “during the latter part of July, and the beginning of August, a number of the distressed inhabitants of St. Domingo, who had escaped the destruction of fire and sword, arrived in the city. Soon after their arrival the influenza made its appearance, and spread rapidly among the citizens.” The yellow fever quickly followed; for on the 5th of August the Doctor mentions his being called to his first patient. To the same purpose we are informed by Dr. Clarke that “the fever made its appearance in Dominica about the 15th of June, 1793, a few days after the arrival of a great number of French emigrants. They were not sick, and the fever had not made its appearance in Martinique when they left it. From the 1st of July to the 1st of October it was computed that eight hundred emigrants, including their servants and slaves, were cut off by this fever; and about two hundred English, including new comers, sailors, soldiers and negroes, all fell victims to it in the same space of time. Few new comers escaped an attack, and few recovered. It spared neither age nor sex among the Europeans and emigrants; and not only the people of colour from the other islands, but the new negroes who had been lately imported, were all attacked. Such as had been long on the island escaped.”[181]
These facts seem to point out one of the causes, and very probably a principal cause, of this dreadful distemper. They show very evidently that there is a connexion between war and diseases. It has formerly been attempted to point out a natural connexion between the horrid practices of men, on these occasions, and the production of disease. These investigations, however chimerical they may be reckoned, are yet supported by many facts, which undoubtedly prove that mankind cannot always maltreat and torment one another with impunity. The affair of the Black assizes, and Old Bailey session, in 1750, shows, that by confinement and bad usage the human body, without being apparently deprived even of health, may become poisonous to those around it, and produce dreadful diseases. In like manner the inhabitants of St. Domingo, having been put to the most dreadful distress, became properly fitted for spreading destruction wherever they went.[182] It is even probable that, in proportion to the degree of distress suffered by these people, the disease communicated by them will be malignant; nay, that new diseases may spring up, which cannot be treated with success by any method yet known to physicians. With regard to the disease in question, it seems plainly to have from some cause or other received an additional malignity. Dr. Chisholm says that what he calls the Boullam fever was supposed in Grenada to have been the common yellow fever of the West Indies engrafted on the jail fever. Dr. Lind, Dr. Jackson, and even Dr. Chisholm himself, agree that the former is not infectious: but from what has been already said the evidence seems to prevail in favour of the opinion that the latter is so. Should we then allow that two kinds of this fever might exist at the same time, in one city, the difficulty would be at once removed. But this has been reckoned by many, particularly by Dr. Rush, as totally inadmissible; and indeed it is a maxim consonant to general experience, that two epidemics cannot exist in one place at the same time, or that two diseases can scarcely exist at once in the human body. This however must be understood, principally at least, of acute diseases, or such as affect the whole system; for if any disease of a particular part shall take place, it does not seem impossible that a fever may be superadded to such local disease. The following considerations may perhaps throw some light on the subject:
It appears from the experiments of Dr. Adair Crawford, that, when animals are immersed in hot water, the blood drawn from a vein is of a florid red colour. In summer it is likewise observed to be of a more florid colour than in winter. If heat thus gives a more bright red to the blood, it undoubtedly also makes it more fluid, and in proportion to its fluidity it will likewise become acrimonious; though this acrimony is not necessarily connected with a florid colour, as the blood of the arteries is not more so than that in the veins. In the yellow fever, however, the blood sometimes, towards the end of the disease, becomes endowed with extreme acrimony. Dr. Smith, in one of his letters to Dr. Buel, observes, that “blood drawn in the fever of 1795 was remarkably wanting in floridity; especially what was evacuated towards the close of the disease, whether by art, or spontaneous effusion. In one instance it seemed endowed with a caustic quality, and affected a lancet so as to leave a permanent discolouration and inequality on its surface.” He observes also, nay, considers it as demonstrated, that the yellow fever is not a disease of vascular debility, and he says that it is attended with an astonishing fluidity, or, as it is called, dissolution of the blood. Every one therefore who comes from a cold to a warm climate must in some degree or other have his blood liquefied, and in a certain proportion rendered more acrimonious than before. This acrimony may be undoubtedly augmented by certain causes, and by none more probably than immoderate drinking of spiritous liquors. Every one therefore who comes from a cold country to a warm one, especially where the air is also moist, may consider himself as already diseased, at least in comparison with what he was when at home. For the blood is now exposed to a greater degree of heat, and consequently is about to absorb, or rather may be considered as in the act of absorbing, more, and consequently of changing from a thicker to a thinner or more fluid state; the latter being the natural situation of the blood in warm countries. Dr. Rush, in his inquiry into the proximate cause of fever, has accounted for the dissolved appearance of the blood in malignant fevers to a tendency in the blood-vessels to paralytic affection. He says that “it (the dissolution of the blood) begins in the veins, in which muscular action is more feeble than in the arteries. This has been proved by Dr. Mitchill in his account of the yellow fever in Virginia in 1741. He found the blood to be dissolved when drawn from the veins, which, when drawn from the arteries of the same persons, exhibited no marks of dissolution.” This, as the Doctor observes, “is a fact of great importance;” only we must remember, that, in every thing relative to the human body, when we find two phenomena constantly accompanying each other, it is extremely difficult for us to determine which is cause or effect. Instances of this often occur; and in the present case the dilemma is as great as any other. Though, from the testimony of Dr. Mitchill, we cannot doubt that in yellow fever the dissolution begins in the veins; and though it is likewise extremely probable that this dissolution is attended with a paralytic tendency, we cannot know whether the dissolution is the cause of the paralytic tendency, or the paralytic tendency the cause of the dissolution. The point, however, is of no importance. We see that in warm climates the blood of a person newly arrived has a natural tendency to dissolution, and of course the veins to the paralytic affection just mentioned. The liver therefore, which is supplied with blood by a large vein branched out like an artery, and terminating in other veins to carry back the blood from the former,[183] must be much more affected than any other part of the body; and this indeed seems a very probable reason why all those who come to warm countries become much more inclined to bilious complaints, which denote an affection of the liver, than they were before. This hepatic affection may very probably be greatly augmented, in new comers, by various causes. One of these is hard labour under a greater heat than they have been accustomed to; a second, that in the West India islands they have not access to that plentiful supply of fermented liquor, abounding in fixed air, which they had at home. This, though not generally taken notice of, is far from being a matter of little consequence; for, though emigrants from Britain and Ireland have been for the most part accustomed to drink spiritous liquors, yet fermented malt liquors certainly constitute the principal part of their drink. The total want of these, and the substitution of ardent spirit and water, must certainly be detrimental, even though they keep within the bounds of moderation, and much more if they do not. Dr. Moseley relates,[184] from Dr. Irving, that, in a bad kind of intermittent which broke out among the troops in service on the Spanish main in 1780, “nothing was so grateful as London bottled porter. Wine was neither so much desired by the sick, nor so serviceable in corroborating and keeping up the powers of the stomach; which, like the rest of the body, was soon reduced, from the slightest indisposition, to the lowest state of debility.” A third cause is no doubt their frequently drinking too freely of spiritous liquors, perhaps not of the best quality; and which, as they are neither conjoined with the fixed air nor with the mucilage which as it were inviscate and blunt their force in malt liquors, cannot fail of exerting their deleterious properties in a very remarkable manner.