EPIDEMICS

EXAMINED AND EXPLAINED:

OR,

LIVING GERMS

PROVED BY ANALOGY TO BE

A SOURCE OF DISEASE.

BY

JOHN GROVE, M.R.C.S.L.

AUTHOR OF "SULPHUR AS A REMEDY IN EPIDEMIC CHOLERA."

LONDON:

JAMES RIDGWAY, PICCADILLY.

MDCCCL.

"The tendencies of the mind, the turn of thought of whole ages, have frequently depended on prevailing diseases; for nothing exercises a more potent influence over man, either in disposing him to calmness and submission, or in kindling in him the wildest passions, than the proximity of inevitable and universal danger."—Hecker's Epidemics of the Middle Ages.

"The grand field of investigation lies immediately before us; we are trampling every hour upon things which to the ignorant seem nothing but dirt, but to the curious are precious as gold."—Sewell on the Cultivation of the Intellect.

TO

BENJAMIN GUY BABINGTON, F.R.S., M.D.,

PHYSICIAN TO GUY'S HOSPITAL,

AND

PRESIDENT OF THE EPIDEMIOLOGICAL SOCIETY,

ETC. ETC.

THESE PAGES ARE, BY HIS KIND PERMISSION,

Respectfully Dedicated,

BY HIS OBLIGED AND FAITHFUL SERVANT,

THE AUTHOR.

PREFACE.

The following pages have been written with a view to render some aid in establishing a sound and firm basis for future research, on that absorbing topic, the Causes and Nature of Epidemic Diseases.

The amount of information already published on Fevers, on the Exanthemata, and on the Plague, is truly astonishing, and the more so when it is considered, that at present no rational account or explanation is given of the causes of these affections.

It appears to me but reasonable to suppose that as every thing on this earth has been created on a wise and unerring principle, Epidemic and Infectious Diseases are only indicative of some serious errors in our social arrangements and habits. The dangers and misery brought upon us by disease, may, as shewn by Dr. Spurzheim and Mr. Combe, be warnings against the infringement of the natural laws.

Indeed, what is more rational than to suppose that the Seeds of Disease are coeval with the fall of man. His first disobedience

brought death:—that his subsequent errors should hasten its approaches is not to be marvelled at. The undetected murderer, though he may escape the punishment human justice would inflict upon him for his delinquency, suffers a penalty in the tortures of conscience, infinitely more horrifying than the most ignominious death. The law of nature is triumphant.

No less certain, though after a different manner, are the consequences of minor forms of disobedience. It is so ordained, that certain diseases shall arise, under peculiar conditions, which may have been brought about by a train of causes, easily imagined, and difficult to be explained, but all having their origin in the vices and errors of man in his moral and social relations.

If man neglects the cultivation of the ground; with rank vegetation, the germs of fever will invisibly grow and multiply; if he harbours that which is rotten and corrupt, he is himself consumed by those agents destined to remove the rottenness and corruption; it is a part of the law of nature that there should be active and energetic agents for this purpose. The seeds of disease, like the seeds of plants, may be shewn to have

their indigenous localities; like them they may be spread and multiplied; like them they may lie dormant, and after awhile spring as it were into active existence; like them, when the soil and other conditions favour, they are ever ready to make their appearance. And this is the law, the germs of all disease exist, and have existed. Despise the dictates of nature, be careless of yourself and those around you, neglect to use the means which a noble intelligence has placed at your command, and above all, transgress the laws of God, then will disease pursue and attend you, as the conscience of the murderer pursues and attends him until he is finally cut off.

His wants and necessities, his sufferings and privations, are the basis of the intellectual progress of man. The wonders of Omnipotence are revealed through the whirlwind, the storm, the pestilence, and the famine.

The constructive and perceptive faculties of man have been developed by the necessity of protecting himself from injury by winds and rains; his intellectual faculties have been cultivated, by the sufferings of disease having led him to the study of

organization and life, to discover the cause,—and to chemistry, and other sciences for the cure of his ailments.

Famine and distress have aroused his emotions, and softened down his asperities, so that what appears at first to be the infliction of a Curse without Pity, is in reality a Judgment with Mercy.

It occurred to me, that on the formation of the Epidemiological Society, the first question for consideration should be, What is the nature of those agents, which induce Epidemic Diseases? are they composed of animate or inanimate matter? In other words, do the manifestations of these diseases exhibit the operations of living or of chemical forces.

Having, in my study, dwelt on the subject with an earnest desire to find the truth, I put the suggestion, with my ideas, before the public to reject or receive them. If they be rejected, I can but think a full discussion of the enquiry will lead to the most important results. If they be received with favour, I doubt not others, with more ability, will take up the strain and resolve the discords into harmony.

J. G.

Wandsworth, September, 1850.

CONTENTS.

INTRODUCTION.

It is one thing for a man to convince himself, but a very different thing to be able to convince others.

I am not now speaking of a conviction arising from the impression made by a few startling facts, nor of one forced on the mind by early prejudices, or by the dogmas of the schools, but of a conviction arising from careful enquiry.

In the course of that enquiry, the collector of facts, sees their relations to the idea in his mind, in a multiplicity of ways, from their remaining, each, as one succeeds the other, an appreciable time on the sensorium, and undergoing a certain process of comparison and relation, with all other facts and ideas which have been previously stored up. As the materials for an edifice which have been shaped and prepared in accordance with the completion of the design, so do the facts and ideas which are accumulated

in the mind, become shaped and prepared for the elimination of a truth. The ultimate design of the architect can no more be conceived by the examination of the framework of a window, or the capital of a column, than the whole truth of a proposition by the examination of separate facts; the whole must be conceived and all the relations of all the parts thoroughly understood, before the architect can be comprehended or the harmony of his design appreciated.

The process of thought in the minds of the architect, and in the framer of a proposition, is never exactly the same as in those who contemplate and examine their completed works. Much may be done, however, by both to aid others in comprehending them. The more accurately they keep in view the course their minds have taken, the more readily will their descriptions be understood.

To simplify the elements of our knowledge is to give others a ready access to our thoughts.

To arrange the course of our ideas in harmony with the elements of our knowledge should be the end of all writing, as it is the only means of multiplying knowledge.

It is not the mere accumulation of facts which constitutes science, any more than a collection of building materials constitutes a house, it is the arrangement and adaptation of the means to the end by which the house becomes built and science cultivated.

These reflections have been suggested by the circumstance that for the last 3000 years and upwards, Pestilences have at certain intervals done their work of destruction, and opened the springs of misery to untold millions, and yet I see not that we are much further advanced as to the knowledge of the cause of these inflictions than the Jews in the time of Moses. In the Levitical law, as I shall have occasion more particularly to shew hereafter, were directions specially given in reference to the plague of leprosy; what means should be adopted for the cure of the disease, and for preventing its extension, and moreover pointing very significantly to certain facts having connexion with the cause of the affection. Since that time historians generally, and medical writers in particular, have diligently recorded their observations and accumulated facts, on the various desolating plagues which

have afflicted mankind. Some of these men have grappled with the whole subject, and endeavoured to shew the presumed relation of the supposed causes in all their intricacies, but it is hardly necessary to say that all have signally failed in their attempts to furnish us with any practical information.

Satisfied in my own mind that the whole subject is beyond the labour of one man, and impressed with the belief that the basis of the enquiry is in anything but a satisfactory state, I have applied myself entirely to the study of the groundwork only, as the primary proceeding for a solid superstructure.

The days are past, when imaginary spirits, ethers, and astronomical phenomena, were believed to have any essential influence over our destinies in a physical point of view; we have therefore to deal with matter in some form or other.

The question, therefore, which I have proposed for enquiry, is, whether the matter which causes epidemic and endemic diseases, exhibits the properties of inorganic or organized matter.

The properties and qualities of organized

bodies, as well as those of inorganic matter, need but be stated, and in some instances we may picture to ourselves the object, without having seen it, and not be very far from a true conception. But for this purpose a clear and definite idea must be previously formed, and have taken possession of the mind, of the great general divisions of objects in the material world.

Having made these preliminary remarks, I have suggested a certain mode of procedure in making enquiries of this kind, not perhaps in strict accordance with logical systems, but on the principle of nature's operations in our own minds, which appears to me, when reduced to a systematic and simple form, to be sufficiently clear and strict for synthetical application, and so concise as to be usefully and practicably applied.

In endeavouring to establish a theory for the explanation of extraordinary phenomena, there are certain rules which should guide us in the thorny and treacherous path of speculation. But these rules readily flow from the train of thought, and if we examine our own minds during their operations, we

shall find that the following is the course of our instinctive reflections. It is a course we adopt as the test of theories when formed, and is a guide in all cases for their construction.

We first commence with an idea, which exists in our minds in the form of a proposition: then the following rules naturally suggest themselves:—

1. The probability of the value of our proposition from inference.

2. The number and value of facts to support the proposition.

3. The reasonableness of the application of the facts to the inference.

4. What amount of information in the form of results can be produced in proof of the tenableness of the proposition.[^[1]]

In illustration of the value of these rules the history of Dr. Jenner's discovery affords an appropriate example. To use the words of Dr. Gregory, "he appears very early in

life to have had his attention fixed by a popular notion among the peasantry of Gloucestershire, of the existence of an affection in the cow, supposed to afford security against the Small Pox; but he was not successful in convincing his professional brethren of the importance of the idea."

The popular notion of the peasantry originated the idea in Jenner's mind, and it became fixed there as a proposition.

1. He commenced his enquiry by observing that the hands of milkers on the dairy farms were subject to an eruption, and he inferred that the notion of the peasantry bore the stamp of probability, which strengthened the idea in his mind and gave force to the proposition.

2. His next step was to accumulate facts; he found on enquiry that the persons engaged on these farms in milking, possessed an immunity from Small Pox to an extent sufficient to strengthen the value of his proposition.

3. The reasonableness of the application of the facts to the inference is clear from the coincidence that the eruption on the hands of the dairy people bore a striking

resemblance to the Small Pox, and as this disease does not usually occur twice in the same individual, the inference was most reasonable that this eruption protected the people from Small Pox.

4. We have but to take the almost universal adoption of vaccination, and its acknowledged prophylactic powers against the propagation of Small Pox to shew the application of our fourth rule.[^[2]]

Between the conception of the idea and the accomplishment of Jenner's designs, vaccination seems to have undergone an incubation of nearly twenty years. During that period, with an energy and perseverance only to be obtained by confidence, did this great man brood over and elaborate his idea; and well might the 14th day of May,

1796, be styled the birth day of vaccination, for on that day was a child first inoculated from the hands of a milker.

In adopting the above method I have endeavoured to bear in mind M. Quetelet's observations on the requirements necessary for medical authorship; he says, "All reasonable men will, I think, agree on this point, that we must inform ourselves by observation, collect well-recorded facts, render them rigorously comparable, before seeking to discuss them with a view of declaring their relations, and methodically proceeding to the appreciation of causes."

CHAPTER I.

IS IT PROBABLE THAT EPIDEMIC, ENDEMIC, AND INFECTIOUS DISEASES, DEPEND UPON VITAL GERMS FOR THEIR MANIFESTATIONS?

It is, I believe, almost universally considered that Epidemic, Endemic, and Infectious diseases, originate from some imaginary poisons of a specific nature, each disease having its own peculiar poison. That this conception should have taken possession of the minds of men, is most natural from the symptoms which characterize these diseases, but when we come to enquire into the nature of these agents, or supposed poisons, we are at once struck with the idea that they exhibit one peculiarity which separates them in a marked manner, from those poisons with which we are familiar; for the poisons of Small Pox, Measles, Scarlet Fever, Hooping Cough, Fever, &c. possess the power of multiplication, or spontaneous increase, a property which attaches only to the organic kingdom, and is never known in the inorganic kingdom. The source of most of the poisons is to be found among mineral or vegetable products. A mineral in combination with an acid or oxygen may become a poison, and

nitrogen in various combinations with oxygen, hydrogen, and carbon, or with carbon alone, may become a poison; these combinations are, however, in most instances the products of vegetable life, others again are obtained from the animal kingdom, such as the poison of the serpent, &c. but in all of these instances, there is not one in which the power of self-multiplication is to be found.

We are, therefore, constrained to admit that this feature, which distinguishes poisons, is one well worthy attentive consideration. The varieties of poisons may be classified into those which act topically as escharotic poisons, those which act chemically on the blood, and those whose effects are manifested in inducing a speedy annihilation of organic or vital action, as in the case of hydrocyanic acid, which is supposed specifically to affect the nervous centres from which originate the vital manifestations. It is rather remarkable that the vital poisons (as I will call them for distinction), seem to have their appropriate locality in the blood, they do not primarily affect one organ more than another, all the effects we witness resulting from them are to be traced progressively from the blood to other parts of the body. When a person is inoculated with small pox, a very minute portion (indeed it is impossible to say how minute it may be) is sufficient, when absorbed, to excite a certain train of symptoms, all due to absorption of the materies of the disease, and the process by which

that materies arrives at maturity, is that known in the vegetable world as the fructification; this process of fructification is a process of development and increase.

I here may repeat that among all the poisons known, constituted as they are of various combinations of elementary matter, they are without exception destitute of the power of development or increase. Now, it is pretty accurately known what amount of these poisons is necessary to produce their effects on the living body; we can say how many drops are sufficient of hydrocyanic acid of Scheeles strength, to destroy a man instantaneously. Again, how many grains of arsenious acid are sufficient to induce such an inflammatory condition of the stomach and intestine as will end in death, and how many grains of morphia, will bring about a fatal coma,—but who shall say the amount of the vital poisons necessary to produce their results? It far exceeds the limit of conjecture, to what extent the dilution of miasmatic or contagious matter may be carried, and the poison yet be capable of committing in a short time the most frightful ravages.

We may fairly then infer, that if a quantity of matter inappreciable in amount be sufficient to exhibit the characters of growth and increase, that it is endowed with the properties of vitality. That the poisons of scarlet fever, of measles, and of small-pox have this power of growth and increase, is as much a matter of universal belief as that "the sun

will rise and set to-morrow, and that all living beings will die."

This power of individual increase, or reproduction, is the very summit of vital manifestation; indeed Coleridge, in his Theory of Life, (in which he says, "I define life as the principle of individuation, or the power which unites a given all into a whole that is presupposed by all its parts,") places reproduction in the first rank, and expresses his hypothesis thus: "the constituent forces of life in the human living body are, first, the power of length or reproduction; 2nd, the power of surface, or irritability; 3rd, the power of depth, or sensibility—life itself is neither of these separately, but the copula of all three."

Extensive research is not required to shew that many thinking men believe in the existence of living organic beings, as the elements of contagious and epidemic diseases; the idea indeed seems to flow spontaneously in that direction. Whenever thought, and enduring contemplation, have been concentrated on the subject, the result appears to have been the same, a firm conviction in each individual mind that a vital force must be in operation; or as Schlegel would define it, "a living reproductive power, capable of and designed to develope and propagate itself."—"Its Maker originally fixed and assigned to it the end towards which all its efforts were ultimately to be directed."

Referring further to beings having the property of reproduction and propagation, he says, (using

the word nature here evidently as the vital principle for want of a better term,) "Nature indeed is not free like man, but still is not a piece of dead clockwork. There is life in it."—"Thus we know that even plants sleep, and that they too as much as animals, though after a different sort, have a true impregnation and propagation."

When Schlegel wrote this, how little could he have imagined the intricacy of this proceeding among the lower forms of vegetation. It has been shewn by Suminski, and verified by many others, that the mode of impregnation, and the period at which it occurs in the ferns, do not at all correspond to the general notion on this subject. He has discovered in the early development of the frond of ferns certain cells, which he denominates antheridia, or sperm cells; these contain in their cavity a number of subordinate cells, each containing a spermatazoon. At a certain period of the progress of the frond, the parent cells become ruptured and liberate the spermatoza, these move about in a mucilaginous fluid, which bedews the inferior surface of the frond, and become the means of impregnating the germ cells, or pistillidia, with which they readily come in contact. Thus the process of impregnation in these plants occurs during the germination, or what corresponds to the period of germination in the seeds of exogenous and endogenous plants.

I have referred to the discovery of Suminski in

this place to recal to the mind the great and incomprehensible wonders of creation, for who could conceive it possible or feasible that even for the impregnation of an inferior vegetable, animal life should form an indispensable and essential appurtenant of the process. Truly may we say with Coleridge, of plants and insects, "so reciprocally inter-dependent and necessary are they to each other, that we can almost as little think of vegetation without insects, as of insects without vegetation."

I will make but two more quotations on the supposed vital character of the germs of disease. "That the air and atmosphere of our globe is in the highest degree full of life, I may, I think, take here for granted, and generally admitted. It is, however, of a mixed kind and quality, combining the refreshing breath of spring with the parching simooms of the desert, and where the healthy odours fluctuate in chaotic struggle with the most deadly vapours. What else in general is the wide-spread and spreading pestilence, but a living propagation of foulness, corruption, and death? Are not many poisons, especially animal poisons, in a true sense, living forces?"—Schlegel.[^[3]]

It were useless to multiply quotations to shew

that the opinions here entertained are matters of general belief among thinking men.[^[4]] I will at once then conclude with an observation of Dr. C. J. B. Williams: he puts the question, "Does the matter of contagion consist of vegetable seeds? Are infectious diseases the results of the operations and invasions of living parasites, disturbing in sundry ways the structures and functions of the body, each after its own kind, until the vital powers either fail or succeed in expelling the invading tribes from the system?"

And this expression, the seeds, is an universal expression, it is a "Household Word" in connexion with disease. That it has obtained this position in the popular vocabulary is alone a proof of the applicability of the term to the thing intended to be

signified. Popular notions, as we have seen in the case of Jenner's discovery, are not to be unheeded. An instance occurs to me, it was a popular belief, that in acne punctata, the matter of a sebaceous follicle, was itself, when pressed out, a worm, the dark portion which results from the accumulation of dust upon the matter at the mouth of the follicle was supposed to be the head of the maggot, as it was called; subsequent observation, however, has proved that though this matter is not a worm, it contains an animal within its substance, the Acarus folliculorum.

The popular notions found among savage tribes as to the efficacy of certain remedies in the cure of disease have been the means of furnishing us with some of our most valuable medicines, indeed it is almost impossible to say whether originally man did not derive his remedies from the herbs and trees by an instinctive faculty impelling him, as it does the animals when in a state of liberty and with freedom of range, to seek certain plants as they avoid others.

It is well known that animals when indisposed will find out some spot as if almost led to it by a visionary guide where the "healing plant" is to be discovered. I am told that sheep have this faculty, and that they will, when affected with the rot, feed upon some plant when they can discover it, which eradicates the disease.

Almost every one is familiar with the fact that cats and dogs will crop herbage and eat it; I have

seen them frequently leave the house and proceed to the grass in the most business-like manner, partake of some quantity, and quietly return.

A close observer of diseased animals might obtain some useful information by noticing the plants cropped by them while in that condition. The observations should be made in a variety of districts in consequence of the uncertain distribution of some even of the most commonly scattered plants; in one year they may be abundant, but in another they may be almost entirely absent from the same spot.[^[5]]

Were it only on the fact of reproduction, I would be contented to take my stand that the force of life is the indwelling power of pestilential matter. Reproduction is a law of nature, and the law of nature is the law of God. And where do we find He prevaricates with us? The more we study His laws the more harmony and perfection we find; what is seeming confusion in the ignorance of to-day, is order in the knowledge of to-morrow. If any one ignorant of the law which regulates the diffusion of gases were

told that a heavier gas would ascend contrary to its specific gravity through the septum in a vessel containing a lighter gas above the heavier, he would naturally doubt your assertion, and say, "that is contrary to the law of gravity;" but explain to him the principle by which this comes about, and the objects of the law; the order and beauty of the design become manifest. But this is no equivocation, it is evidence there, that subordinate laws exist and nothing more. It has never been found that men have gathered "grapes of thorns and figs of thistles," nor has it ever been discovered that inanimate matter multiplies itself. The seed of disease "is within itself," multiplying and propagating itself; whether it formed a part of creation at the beginning or not, is rather a question to be solved by divines than physicians. When we know, however, the latency of seeds and even of entire plants, and that they may be dried and remain so for years yet being brought again into conditions adapted to their active existence, they, as it were, revive from their sleep, and renew again their reproductive properties: can we wonder if, in the great scheme of nature, existences new to mankind should make their appearance? When the New Zealander saw the surface of his ground producing to him unknown plants, and the skins of his children generating peculiar eruptions, and each propagating its kind, would he look, think you, to the wood or the stones, the air or the water,—for the solution of the

mystery? No, he would naturally say these people brought the seeds with them. From the property of reproduction possessed by these forms of matter, we infer the value of the proposition.

CHAPTER II.

THE NUMBER AND VALUE OF FACTS TO SUPPORT THE PROPOSITION.

————

SECTION I.

ON REPRODUCTION.

It is inferred that the proposition, "the matter which operates in the production of Epidemic, Endemic, and Infectious Diseases, possesses the property of vitality," we proceed now to the enumeration of those facts which further elucidate this subject.

The facts must necessarily be such as illustrate the identity of properties in the imaginary germs, that are known to exist in demonstrable germs: we take therefore the law of reproduction to be to life, what the law of attraction is to gravitation.[^[6]]

But further; do those matters which engender disease furnish to our minds the properties inseparable from life in the abstract? Though the faculty of reproduction is essentially an evidence that the thing which reproduces its kind must be a living body, yet it is only a property or power of living beings and is not itself life, it therefore is necessary to establish the fact that the materies morbi not only has the power of reproduction, but also those properties which in the abstract will prove as far as demonstration can go, that it has the essential properties common to all living bodies.

I must again quote from Coleridge, he says: "By life I every where mean the true idea of life, or that most general form under which life manifests itself to us, which includes all its other forms. This I have stated to be the tendency to individuation and the degrees or intensities of life, to consist in the progressive realization of this tendency. The

power which is acknowledged to exist wherever the realization is found, must subsist wherever the tendency is manifested. The power which comes forth and stirs abroad in the bird, must be latent in the egg."

The tendency to individuation cannot be more strongly marked than in the simple experiment of vaccination: we insert a small particle of the so-called vaccine lymph under the skin, and by this means we multiply to an enormous extent, the power which, in the first instance, we had in the form of minute corpuscles in a dry and apparently inert state; nevertheless, though in this condition there must have existed the tendency to individuation or multiplication of individual existence, and the germs are here to their active existence, as seen in the development of the vaccine vesicle, what the egg is to the bird,[^[7]] as described above; we may, therefore, say that the power which exhibits itself in the production of a vaccine vesicle, must have been latent in the dried matter. It is the opinion of Muller that the entire vital principle of the egg

resides in the germinal disk alone, and since the external influences which act on the germs of the most different organic beings are the same, we must regard the simple germinal disk, consisting of granular amorphous matter, as the potential whole of the future animal, endowed with the essential and specific force or principle of the future being, and capable of increasing the very small amount of this specific force and matter, which it already possesses, by the assimilation of new matter.

After speaking of inanimate objects, Dr. Carpenter says; "and what compared with the permanence of these is the duration of any structure subject to the conditions of vitality? To be born, to grow, to arrive at maturity, to decline, to die, to decay, is the sum of the history of every being that lives; from man, in the pomp of royalty, or the pride of philosophy, to the gay and thoughtless insect that glitters for a few hours in the sunbeam and is seen no more; from the stately oak, the monarch of the forest through successive centuries, to the humble fungus which shoots forth and withers in a day."

To be born, signifies the faculty of reproduction existing or having existed in an antecedent being to that one born, and also that itself possesses equally a like power. To be born, is the first expression which must be used in speaking of the faculties or properties of living beings as independent existences, the annual formation of buds, trees, and shrubs, is a multiplication of the species; the coral

and various budding polypes increase by this process, indeed what is the seed of a plant, or the egg of a bird, or the ovum of mammalia, but cast off buds; in all, the new being was originally a portion of its parent, and if we examine the ovary of the vegetable, the bird, or the mammal, can we find any expression more fitting to designate the process than that of budding. To be born then, is the evidence of an act of one living being, and the commencement of a series of vital phenomena in another, but all these are subsequent to reproduction, and constitute another chain of vital acts, all tending to a similar result, the multiplication of the species.[^[8]]

Now, whether we apply the philosophical language of Coleridge, or the language of observation of Muller, in confirmation of the doctrine here inculcated, we arrive at the same point.

Do we not witness in the newly formed vaccine vesicle, an increase of the specific force and principle? We certainly have acquired by the process of vaccination a manifold multiplication of power, and is there not also assimilation of new matter in

which this power resides? And does not every particle of this new matter contain within itself the same force and principle, as existed in that which generated it?

"We revert again to potentiated length in the power of magnetism (reproduction); to surface in the power of electricity, and to the synthesis of both or potentiated depth in constructive, that is chemical affinity."[^[9]]

Some may be at a loss to conceive, at first, how irritability may be considered a property of all vegetable matter; that it does exist in some vegetables is certain, but that it does exist in all living beings is equally certain;[^[10]] the term, however, which would appear more appropriate when that irritability does not exhibit itself in an appreciable form, is impressibility. Irritability, as commonly understood, is seen in its highest condition in muscular tissue; but "the irritable power and an analogon of voluntary motion first dawn on us in the vegetable world in the stamina and anthers at the period of

impregnation."—"The insect world is the exponent of irritability, as the vegetable is of reproduction."

The property of irritability attains its acme in man, the most highly organized of all beings; and its gradations pass downwards through the whole scale of animate creation; not so reproduction, for this faculty observes the very opposite direction, for in plants a single impregnation is sufficient for the evolution of myriads of detached lives.

Reproduction is a fact, it is an essential property of life, and is a reality to us from observation; but irritability is not so tangible and demonstrable a property. We nevertheless may assume its universality, from the circumstance that we lose sight of it by imperceptible degrees; the irritability of the sensitive plant is as much irritability as that of the highly organized muscle; but because the faculty evades our perception, "in tapering by degrees, becoming beautifully less," we have no reason for pronouncing its total extinction at any one point of the vegetable kingdom,[^[11]] any more than we should have

in saying that we see the end of the earth, when describing the extent of our vision as we stand on the sea shore. The extreme limit of our vision is the tangent of the circle in reference to our visual organs; but how many tangential points there may be beyond, it is impossible to say without knowing the dimensions of the circle.

I think we are now in a condition to assume, as far as abstraction will conduct us without proceeding to an extreme length, that the materies morbi, or, as I will now call them for the sake of clearer distinction, semina morbi, possess those properties which in the abstract are common to all living beings.

Another argument strikes me as capable of adding further strength to the proposition. We need but be told that a small piece of iron was placed in a certain position with regard to another piece of iron, and that the smaller piece moved through a given space and became attached to the larger, to infer that magnetic force was in operation. Supposing this magnet then to be folded in paper, and that it

be promiscuously placed near a compass, the deflection of the needle would indicate that some object in the vicinity was the cause of the deflection; we may farther try what positions the needle takes by varying the position of the packet, and thus point out which is the north and which the south pole of the screw of paper. If we may consider attraction then to be to gravitation what reproduction is to life, we do not err in saying in the one instance that there is a living being, and in the other there is a magnet.

The nebular theory, from which some astronomers made the foundation of many speculations, came with so much interest to our minds that the fascination could not be resisted. It was most delightful to revel in the imagination that we possessed a key to the mode of formation of the starry hosts, and when speculation had taken its extreme limits in the "Vestiges of the Natural History of Creation," and the nebulæ had served as the ground work of a gigantic scheme, Lord Ross's monster telescope swept the heavens of its cobwebs. We can imagine this great promoter of science saying to us, Gentlemen, the clouds which have obscured you, are composed of myriads of stars, and comprise systems as vast and as luminous as our own, had you but power of vision to discern them. A new light thus appeared to philosophers, and though no great practical results may flow from the discovery, it is instructive from the fact that the imperfectly aided or unaided vision, should not limit legitimate

inference. The nebulæ before Lord Ross's discovery were to the astronomer what the materies of epidemic and infectious disease are to medical men. In the absence however of a giant microscope to reveal such great truths, we may yet dimly shadow them by the light of our reason. It was predicted in 1849 that minute vegetable germs, in all probability all of the same type, were the agents producing epidemic and infectious disease. In 1850, Mr. Oke Spooner says,[^[12]] "On examining the matter of Small

Pox and Cow Pox in every stage, he finds its essential character to consist of a number of minute cells not exceeding the 10,000th part of an inch in diameter: being about one-fourth smaller than the globules of the blood, containing within their circumference many still more minute nuclei, and presenting beyond their circumference bud-like cells of the same size and character as those contained within the circle."

Should these observations made by Mr. Spooner turn out to be correct, they will but fulfil my anticipations. Then again shall we see the same application of imperfect vision to the limitation or temporary obstruction of solid and determinate knowledge.

We may reasonably expect that these bodies, discovered by Mr. Spooner, should be the elementary matters of disease. Their existence was predicted from the probability that living matter must be the agent; moreover, that this matter when discovered

would be cellular, most probably resembling the yeast plant as described by Mr. Spooner.

It was predicted that a planet would be discovered in a certain position in the heavens, because the perturbations of a comet indicated an attracting body in the path of the eccentric wanderer; the prediction and the fulfilment were almost simultaneous.

SECTION II.

HISTORICAL NOTICE OF EPIDEMIC DISEASES.

The earliest notices we have of Pestilences are contained in Holy Writ. The plagues which smote the Egyptians in the time of Moses are not unworthy some comment here. Of those ten plagues, four out of the number were due to the miraculous appearance of myriads of the lower animal tribes, in three instances of insects,[^[13]] viz. lice, flies, and locusts; in the fourth, when Aaron stretched forth his hand with his rod over the streams, over the rivers, and the ponds, frogs came up and covered the land of Egypt. In these instances living beings are made the instruments in God's hand for the punishment of the wicked. These plagues include the second, third, fourth, and eighth. The first plague is mentioned as a conversion of the waters into blood. Now if we may take this expression as being literal, there is no reason to suppose that this blood differed in any respect from ordinary sanguineous liquid; we therefore may assume, as the blood is every where in Scripture spoken of as the life, that this fluid was endowed with vital properties.

The fifth plague is described as a murrain among beasts; and the sixth, as exhibiting itself as "a boil breaking forth with blains, upon man and upon beast."[^[14]] Now these affections bear a resemblance to the diseases known to us at the present day through authentic records. The Black Death of the 14th century affords in its history but too awful a picture of the horrors of such pestilences. In the tenth plague, the smiting of the first-born, we are not told by what means it was brought about; but we have something even here to lead us to conjecture. In the second visitation of the Black Death, there were destroyed a great many children whom it had formerly spared, and but few women. The seventh plague of hail is within our conception; as is also that of darkness, the ninth plague.

It is not a little remarkable that of the ten plagues, seven of them depended upon agents intelligible to our comprehension; we can conceive of

the invasion of a country by myriads of loathsome insects and reptiles, and can imagine the wrath of an offended Deity directing the force of a supernatural storm of hail upon a disobedient people; and we can conjecture, though faintly, the consternation of human nature on being subjected to a total darkness of three days' duration, when we consider that darkness has been described, as "a darkness that might be felt."

From this abstract we discover that the three plagues whose causes we cannot understand, or rather upon which no light has been thrown by Scripture, bear analogies to those which we recognise, in the writings of modern authors, as fearful pestilences.

It is now our province to reflect on the causes supposed to be in operation in the three instances, which become naturally separated from the rest.

We are told that a murrain appeared among the cattle, without any preliminary step. When the blains broke out upon man and beast, Moses had been previously directed by the Almighty to take handfuls of the ashes of the furnace, and sprinkle them towards the heaven in the sight of Pharaoh. "And it shall become small dust in all the land of Egypt, and shall be a boil breaking forth with blains upon man and upon beast, throughout all the land of Egypt."

Another coincidence, in connexion with subsequent pestilences, arrests the attention, on the subject of the mysterious appearance on these occasions of

matter resembling dust being prevalent about the houses, and on the clothes of the people. Clouds also, and showers of dust-like particles, were not of infrequent occurrence. Indeed, in the summer of 1849, during the progress of the Cholera, several phenomena of a similar nature were observed and authenticated; I myself can bear testimony to one instance of the kind. It was observed by many persons in my neighbourhood after the passage of an ominous and lurid cloud, that as they walked their clothes became covered with a singular dust-like matter of very peculiar appearance. That this phenomenon was not destitute of significance may be gathered from the fact, that on the night of that day several severe cases of Cholera occurred, though our village had been comparatively free for ten days.

Hecker, in writing on the Black Death says, the German accounts expressly speak of a "thick stinking mist which advanced from the east,[^[15]] and

spread itself over Italy; there could be no deception in so palpable a phenomenon." It is not unworthy of mention, that in the East successive invasions of locusts "which had never perhaps darkened the sun in thicker swarms," preceded the great outbreak of this disease, for they left famine in their train.

From 1500 to 1503 in Germany and France, during the prevalence of the sweating sickness, spots of different colours made their appearance, "principally red, but also white, yellow, grey, and black, often in a very short time, on the roofs of houses, on clothes, on the veils and neckerchiefs of women, &c." Blood rain is also mentioned as having occurred at this time, which consisted of the aggregation of minute particles of red matter.

In the seven plagues, miraculous operations of the Deity consisted in the unusual manifestation of phenomena, but which in their effects are recognizable as of clear and definite import. The miracles here are,—in the mode of producing the swarms of frogs, locusts, &c. but they are manifest and unmistakeable causes of plague and famine; in the other three, on the contrary, we witness only the effects, the causes are hidden from us; we may, therefore, as in current events, legitimately investigate the subject, and what better course can be adopted than that which classifies the traditionary past with all subsequent history. Presuming such a method of research to be admitted, I have assumed that as

the causes of the seven plagues have been distinctly given, the others, though only mentioned in their effects, were due to causes of a nature in some way to be compared with their concomitants, that is to say, if a special intervention of the Deity brought about a miraculous appearance of frogs, lice, &c. there is but little reason to doubt that some other agent was miraculously multiplied and concentrated to induce the murrain, engender the blain, and smite the first-born: as if to lead us into this enquiry, on the visitation of the blain in man and beast, the Bible History tells us that Moses threw ashes of the furnace, which became a dust throughout all the land of Egypt; we cannot imagine that this simply as ashes could have caused the blain, we may conclude that by some special miracle, either the ashes were converted into a specific form of matter capable of inducing the effects recorded, or that an independent septic matter was generated for the purpose. If the latter, the act of throwing the ashes of the furnace into the air may have been intended to signify that the extremely minute division of the particles when thus cast into space, typified the inscrutable and hidden nature of the matter endowed with such marvellous properties.[^[16]]

Further on in the book of Leviticus are passages which I cannot forbear transcribing, for they point out to us most indubitably a line of enquiry in reference to diseases of a contagious nature.

"The garment also that the plague of leprosy is in, whether it be a woollen garment, or a linen garment, whether it be in the warp or woof, of linen or of woollen, whether in a skin, or in any thing made of skin, and if the plague be greenish or reddish in the garment ... it is a plague of leprosy, and shall be shewed unto the Priest, and the Priest shall look upon the plague and shut up it that hath the plague seven days; and he shall look on the plague on the seventh day; if the plague be spread in the garment, either in the warp, &c. ... the plague is a fretting leprosy, it is unclean. He shall therefore burn that garment ... wherein the plague is, for it is a fretting leprosy; it shall be burnt in the fire. And if the Priest shall look, and behold, the plague be not spread in the garment ... then the Priest shall command that they wash the thing wherein the plague is, and he shall shut it up seven days more: and the Priest shall look on the plague, after that it is washed: and behold if the plague have not changed his colour, and the plague be not spread, it is unclean; thou

shalt burn it in the fire; it is fret inward; whether it be bare within or without. And if the Priest look and behold the plague be somewhat dark after the washing of it, then he shall rend it out of the garment ... and if it appear still in the garment either in the warp or the woof ... it is a spreading plague: thou shalt burn that wherein the plague is with fire. And the garment ... which thou shalt wash, if the plague be departed from them, then it shall be washed the second time and shall be clean."—Chap. xiii. 47-58.

Again in Deuteronomy. The curse for disobedience: "The Lord shall make the pestilence cleave to thee until he have consumed thee from off the land.—The Lord shall smite thee with a consumption, and with a fever, and with an inflammation, and with an extreme burning, and with the drought, and with blasting, and with mildew, and they shall pursue thee until thou perish.—The Lord shall make the rain of thy land powder and dust: from heaven shall it come down upon thee until thou be destroyed."

It may be said, and I doubt not will be said, all this is unnecessarily dragging the sacred volume into an enquiry totally foreign to its general tenor; on the contrary, however, I maintain by that Book we are to learn the ways of God to man, and further, that no study can impress mankind with so awful, so terrific an idea of his responsible position, as that which leads him into the investigation of the causes

by which the Almighty, doubtless in His wisdom, has thought fit at various epochs of this world's history, to place man face to face with pestilence, famine and sudden death.

There is no man would less willingly than myself introduce profanely the revelations of Scripture. The observations here made are not, therefore, intended for light or heedless controversy; if they have a significance of any import, let them be alluded to in the same spirit with which they have been quoted; if they convey nothing for approval to the reader, let silence rest upon them. To those who would fain disregard my request, let me recall to their minds the veneration which from childhood I trust we have always felt on hearing or seeing those two words—Holy Bible.

It is yet to be determined, whether the greenish or reddish appearance of the garment spoken of, as being contaminated with the plague of the leprosy had any specific relation to the disease itself. The priest orders that the garment shall be shut up seven days, and on the seventh day, if the plague be increased, by which, of course, is meant if the greenish or reddish colour have increased, and from which we may gather that a power of spontaneous increase was possessed by the matter, such a result indicated a fretting leprosy, and the garment was to be burnt. Again, though there may have been no increase, but a persistence of the coloured matter after shutting up and washing the garment, it is to

be burnt, for it is fret inward, signifying, that the germs of the affection are still there, and may soon increase. Other rules follow in reference to the plague of leprosy, and the mode of deciding whether an article be unclean or clean is definitely laid down, but our purpose is served in mentioning the above, to shew that in the time of Moses the spontaneous increase of certain minute multiplying germs was supposed to have a close connexion with disease. It is equally clear, that the priests were aware by the order given them, that if the ordinary modes of purifying articles of clothing failed in their effect, the safest and surest method of destroying infectious matter was to resort to the practice of consuming by fire all materials capable of propagating an infectious malady.

The facts above noticed, accurately correspond to what we now know as applicable to the matter of infectious and contagious maladies. It is a rule, I believe universally adopted throughout the Poor-houses of this country, to put the clothes of all persons about to become residents in these establishments, into ovens, where they are submitted to a temperature incompatible with the existence of either animal or vegetable life. By this means all living matters are destroyed, but the fabrics and inorganic matters retain their properties intact. This simple proceeding, I am credibly informed, is an effectual preventive of contamination by articles of clothing, a desideratum of no small importance, when it is

remembered that the diseases among the poor owe much of their inveteracy to the accumulation of effete organic matters about their persons and clothes.

A few more observations are called for on the quotation from Deuteronomy, in which allusion is made to living matter being an agent in the production of disease. In the curse upon the children of Israel for disobedience, we read that they are to be smitten with mildew. No further information, however, is vouchsafed to us, nevertheless, we can conceive the wretched condition of those on whom the curse might fall. Again, we find in a continuation of this curse that the Almighty uses means such as He adopted in the sixth plague of the Egyptians. The ashes of the furnace became a small dust in all the land of Egypt, breaking forth with blains upon man and beast. In the curse of the Israelites the words are: "The Lord shall make the rain of thy land powder and dust: from Heaven shall it come down upon thee until thou be destroyed."

It might be conjectured that the absence of rain would be sufficient to account for the extinction of the people on whom the curse was pronounced, by the famine and drought necessarily attendant upon the loss of moisture. But this does not appear to be the meaning of the passage, for the powder and dust are mentioned as the agents of destruction; besides, in the continuation of the curse, the locust is to destroy the grain, the worm the grapes, and

the olive is to shed his fruit; we may thus take for granted that drought and famine are not to be caused by the showering of powder and dust, it must consequently be supposed that the effects of the dust in the instance of the Egyptians are to be compared and classified with those of the dust which smote the Israelites.

As far then as Sacred History conducts us in the enquiry, concerning the causes of pestilences, we gain encouragement in the belief that living germs are the active agents, for in the case of the leprosy, we have evidence of reproduction in connexion with infection, which, if our line of argument be tenable, amounts to demonstration; then, in the other instances of the plagues, by boils and blains, they distinctly bear comparison with the accounts given by profane writers, of the visitations of pestilences on the earth, subsequently to those mentioned in Scripture history.

This leads now to the consideration of recorded facts observed and noted during the various Epidemics in the early and subsequent periods of Man's History, as given by those on whom reliance may be fairly placed.

Setting aside the uncertain information contained in the writings of the Chinese,[^[17]] a people whose

progress in the science and practice of Medicine has nothing to commend it (even as it is at the present day) to the notice either of the physician or the historian, unless it be to the latter as a mark of peculiarity both in a social and political point of view,—passing also over the Egyptians, the Arabians, and the Greeks,—and even Hippocrates himself, we are driven to the Romans for any authentic or precise notice of Epidemic Affections. It has been attributed to Hippocrates that he predicted the appearance of the Plague at Athens,

and that when it was introduced into Greece he dispelled it, "by purifying the air with fires into which were thrown sweet-scented herbs and flowers along with other perfumes."[^[18]] But little advantage can be derived from enquiries concerning the first appearance of any disease, for the probability of discovering the primary cause is certainly a

hopeless case, if attempted by means of the writings of ancient authors, when it is recollected that with all the science and learning of the ancient Egyptians, the use of optical instruments was not comprised among the paraphernalia of their arts. The knowledge that was limited to the powers of natural vision, where the foundation of knowledge is based upon facts obtained through the aid of that penetrator of nature's secrets, the microscope, offers no advantages to the student of the present day.

To say that a disease commenced in the East and travelled westward, and at length found a habitation and a name in every part of the globe, is no more than to say that disease is coeval with the fall of man. The cause is as much hidden in the region of its birth, as in that where it sojourns for a time. The cause of the sweating sickness was as much a mystery in England as in all the other nations of Europe, which were visited by its devastating power. And these observations apply with as much force to one disease as another; for even our indigenous ague, originating in some places so limited that the shadow of a passing cloud may mark the boundary of its dwelling place, as inscrutably evades our vigilance, with all the appliances that art can bring to our assistance, in endeavouring to evoke its extraordinary properties under the cognizance of our senses.

If we weigh the air which carries the poison, or analyze it by the most delicate chemical tests, or

take the weight of the atmosphere which is charged with it, or if we take the blood which carries the germs of the disease to the tissues of the body, and submit them after the work of destruction is accomplished, to the most rigid inspection, we can but exclaim,

"These are Thy marvellous works!"

and confess our total inability to fathom the unbounded.

If then no practical advantage can accrue from investigating the writings of the ancients on these subjects, beyond comparing their historical statements with those of more recent date, our purpose will be served by occasionally embodying any remarkable observations of the former with those of the latter.

In proceeding with this course it were better to confine our minds chiefly to two diseases which appear from history to have been known from the earliest periods, these are the Plague and the Small Pox, mentioning other diseases only en route.

Passing then, to the sixth century of the Christian era for the first distinct and connected account of the Plague, it appears from a host of testimony, that the history of this disease, as given by Procopius, well merits our attention. Drs. Friend and Hamilton, in their Histories of Medicine, and Gibbon, in his History of Rome, are equally warm in their praise of Procopius: the latter says, he "emulated the skill and diligence of Thucydides in the

description of the Plague at Athens." The account given by Procopius of this disease, does not differ materially from that given by subsequent eye-witnesses of similar pestilences. Its point of origin is clearly marked, and its mode of dispersion in all directions distinctly traced from "the neighbourhood of Pelusium, between the Serbonian bog and the eastern channel of the Nile." It commenced in the year 542. It raged in Constantinople in the following year, and it was in this city that our historian gathered the materials which are handed down to us. When, however, we anxiously look for any explanation as to the cause of the malady, we are told that it must have been a direct visitation from Heaven, in consequence of the eccentric characters exhibited in its wide-spreading influence, in not yielding to the scrutiny nor bending to the laws known to prevail, and to regulate the course of other diseases: neither country nor clime, age nor sex, the strong and healthy, nor the weakly and previously diseased, could be said to be free from its indiscriminate destruction.

But some phenomena preceding the outbreak of the pestilence are observed as coincidences by all authors. Gibbon thus writes: "I shall conclude this chapter with the comets, the earthquakes, and the plague which astonished or afflicted the age of Justinian." From the accounts given by this author, earthquakes for some years had been threatening and destroying many portions of the globe,

that in the ruins of cities and in the chasms of the earth, great was the sacrifice of human life. Constantinople, which suffered so severely from the plague is said to have been shaken for forty days. These great disturbances of the globe have been always looked upon as indicating other and important influences of a secret or hidden nature; these impressions on the minds of the people are traceable throughout the histories of all epidemics, and have been sufficiently distinct among the people of our own time, preceding and during the period of infliction.

From this short notice of the Plague of 543, I pass to the ninth century, when Rhazes, the Arabian physician, endeavoured to enlighten the world on the subject of Small Pox.[^[19]] In quoting his opinions, I am not to be understood as subscribing to them, but merely endeavouring to point out some peculiar and interesting observations.

First, then, Rhazes attributes the disease to a condition of the blood, which he thus describes, to shew how it happens that in infancy and childhood the disease is most prevalent, and that old age is

least liable to the affection.[^[20]] "The blood of infants and children may be compared to must, in which the coction leading to perfect ripeness has not yet begun, nor the movement towards fermentation taken place; the blood of young men may be compared to must which has already fermented and made a hissing noise, and has thrown out abundant vapours and its superfluous parts, like wine which is now still and quiet, and arrived at its full strength, and as to the blood of old men, it may be compared to wine which has now lost its strength, and is beginning to grow vapid and sour."

"Now the Small Pox arises when the blood putrifies and ferments, so that the superfluous vapours are thrown out of it, and it is changed from the blood of infants which is like must, into the blood of young men which is like wine perfectly ripened: and the Small Pox itself may be compared to the fermentation and the hissing noise which take place at that time."

But the cause of the disease is simply alluded to by this author, as depending upon "occult dispositions in the air," and as he speaks here of Measles with the Small Pox he goes on to say—"which necessarily cause these diseases and predispose bodies to them." This notion of Rhazes that there is some peculiar condition of the blood which favours a process resembling fermentation is not without interest. The circumstance that individuals are not

usually liable to a second attack of the disease, no doubt directed the attention of this physician to compare the process of fermentation with disease of such a nature, seeing that when the whole of the saccharine matter was converted into spirit, the hissing noise, as he calls it, or the disengagement of carbonic acid gas would cease, and the capacity for fermentation be entirely gone. So that the occult conditions of the air, their power of inducing a disease, and multiplying the matter capable of engendering a similar affection, stood in the mind of Rhazes as analogous if not identical phenomena.

We pass now without further comment to the epidemics of the Middle Ages; and here the work of the philosophical Hecker leaves us little else to desire in the way of information, as far as it is obtainable from published records. From the manner in which he has grouped the facts which presented themselves to his mind in the course of a most laborious research, he has saved the student of this subject much toil in acquiring matter for reflection; he has here but to read and digest.

I know not how to select from this invaluable work the most striking passages, to strengthen and support my hypothesis, for not a page is destitute of facts corroborative of the doctrine that vital germs are the material agents of pestilential disorders. The opening paragraph to the Black Death is a most cogent illustration of the assertion; it is, as it were, the theme of the work. "That

Omnipotence, which has called the world with all its living creatures into one animated being, especially reveals himself in the desolation of great pestilences. The powers of creation come into violent collision; the sultry dryness of the atmosphere; the subterranean thunders; the mist of overflowing waters are the harbingers of destruction. Nature is not satisfied with the ordinary alternations of life and death, and the destroying angel waves over man and beast his flaming sword."

I must here apologise for large transcripts from Hecker's work, for neither could I command the amount of knowledge there displayed, nor use such appropriate language as the learned translator has employed.

It is not doubted that the Black Death was an Oriental plague, only of more than usual severity, and wider spread influence of the infectious nature of this disease, and the active properties of the matter producing it. Hecker says, "articles of this kind—bedding and clothes—removed from the access of air, not only retain the matter of contagion for an indefinite period, but also increase its activity, and engender it like a living being, frightful ill consequences followed for many years after the first fury of the pestilence was past."[^[21]]

As extraordinary atmospheric and telluric phenomena preceded the Plague in the time of Justinian, so do we find similar instances recorded as the precursor of a similar visitation 700 years later. I am concerned more with those circumstances which refer more especially to my subject, viz. the development of organic matter, and the peculiar odours of the atmosphere, the latter being evidence of some foreign and unusual production in our respiratory media. "On the island of Cyprus, before the earthquake, a pestiferous wind spread so poisonous an odour, that many being overpowered by it, fell down suddenly and expired in dreadful agonies. A thick stinking mist advanced from the east, and spread itself over Italy."

It is probable that the atmosphere contained foreign and sensibly perceptible admixtures to a great extent, which, at least in the lower regions, could not be decomposed or rendered ineffective by separation. In 1348 an unexampled earthquake shook Greece, Italy, and the neighbouring countries. During this earthquake the wine in the casks became turbid, a proof that changes causing a decomposition of the atmosphere had taken place. "The insect tribe was wonderfully called into life, as if animated beings were destined to complete the destruction which astral and telluric powers had began."

"The corruption of the atmosphere came from the east, but the disease itself came not upon the wings of the wind, but was only excited and increased by the atmosphere where it had previously existed."

"The most powerful of all the springs of the disease was contagion; for in the most distant countries, which had scarcely yet heard the echo of the first concussion, the people fell a sacrifice to organic poison, the untimely offspring of vital energies thrown into violent commotion."

"After the cessation of the Black Plague, a greater fecundity in women was every where remarkable, a grand phenomena, which from its occurrence after every destructive pestilence, proves to conviction the prevalence of a higher power in the direction of general organic life."

In the article Contagion, of the Essay, Sweating Sickness: "Most fevers which are produced by general causes, propagate themselves for a time spontaneously." "The exhalations of the affected become the germs of a similar decomposition in those bodies which receive them, and produce in these a like attack upon the internal organs, and thus a merely morbid phenomenon of life, shows that it possesses the fundamental property of all life, that of propagating itself in an appropriate soil. On this point there is no doubt, the phenomena which prove it have been observed from time immemorial, in an endless variety of circumstances, but always with a uniform manifestation of a fundamental law."

Mead, in his Essay on the Plague, makes many observations of great interest and worthy a physician of eminence; and where, in recent times, shall we look for any more definite information concerning the causes of pestilences? It is not a little singular that at the time this book was published, it was read with such avidity that it went through seven editions in one year.[^[22]] From this circumstance we may gather that the public generally took a lively and proper interest in a subject that was not only of domestic, but national importance. Whether this interest was stimulated by the fact that the work was written expressly by order of the

government, it is now impossible to say, at any rate much credit is due to the Lords of the Regency for having placed so important a duty upon one so thoroughly and in every way so duly qualified for the task as Dr. Mead. It had been well if some of the advice given at that time, as means of protection against the Plague, had been applied and put in force during the late visitation of epidemic Cholera, for, however the minds of some may be convinced of the non-contagiousness of Cholera, there are many who hold a different opinion, and all will acknowledge, that if not strictly a contagious affection, it is clearly proved to be capable of being carried from place to place, or to use Dr. Copland's words, it is "a portable disease." But this is not the place to discuss the subject of contagion, allusion will be made to it hereafter. To return, Mead's expressions are singularly illustrative of the vital power possessed by the germs of disease; he says, "There are instances of the distemper's being stopt by the winter cold, and yet the seeds of it not destroyed, but only kept unactive, till the warmth of the following spring has given them new life and force. His confession as to the hidden cause of the disease, is worthy transcribing: "We are acquainted too little with the laws, by which the small parts of matter act upon each other, to be able precisely to determine the qualities requisite to change animal juices into such acrimonious humours, or to explain

how all the distinguishing symptoms attending the disease are produced."[^[23]]

On the spread of the Plague is the following:—"The plague is a real poison, which being bred in the southern parts of the world, maintains itself there by circulating from infected persons to goods, that when the constitution of the air happens to favour infection, it rages with great violence." Contagious matter is lodged in goods of a loose and soft texture, which being packed up, and carried into other countries, let out, when opened, the imprisoned seeds of contagion, and produce the disease whenever the air is disposed to give them force, "otherwise they may be dispersed without any considerable ill effects." Gibbon thus speaks of the above quoted work: "I have read with pleasure Mead's short but elegant Treatise concerning Pestilential Disorders;" many also might read it at the present day with infinite advantage. Mead most satisfactorily combats the opinions of the French physicians who maintained the non-contagiousness of the Plague. Experience proves beyond doubt, that certain conditions of atmosphere, of

which we are ignorant, favour the growth and increase of pestilences as they do of all vegetation.

Dr. Bancroft was of opinion that specific contagions are each and severally creatures of Divine Wisdom, as distinctly and designedly exerted for their production, as it was to create the several species of animals and vegetables around us.

The indigenous fever of Ireland, which has several times shewn itself in an epidemic form, appears to have been as fatal, as the Plague in the South of Europe. Its devastations have generally been associated or preceded by famine and general distress. Dr. Harty, writing in 1820, says that thrice within the last eighty years has the same fever appeared in its epidemic character. In the year 1741 Ireland lost 80,000 of her inhabitants from this cause. It is a maculated typhus, and considered to be a special product of the Emerald Isle. It has been shewn that fever began to exceed its ordinary rate in those places first where famine and want of employment were most severely felt,[^[24]] and that in such places and under such circumstances, it was most prevalent and fatal. The physicians generally believed it to have been spontaneously produced and not to have been imported. In the last Famine Fever of Ireland, Liverpool and several other places suffered severely from the

importation of their Channel neighbours with the disease in some instances, and the infection in others about their persons. Hitherto these have to all appearance been the limits of the affection; we know not, however, how soon the time may come when the invisible bonds which have thus chained the disease to certain localities may be severed, and spreading itself like other pestilences in an aggravated form, attack this country as a last and crowning act of retributive justice. At present it has but cost us money and regrets, but if the history of pestilences is to be heeded, there are many tokens which seem to indicate that a few slight concurrent circumstances only are wanting, to bring the full force of this disease upon us; then will there be a sacrifice of life. Edinburgh and other towns of Scotland have had some visitations already, ourselves but slightly, but let our labouring population suffer to any large extent for want of work, and we shall inevitably be the sufferers from that fever which in consequence of general destitution is now always more or less prevalent in Ireland.

The Sweating Sickness prevailed in England alone at first, but at length sought foreign victims. The Cholera is an exotic disease, as well as the Plague, but they occasionally have visited our shores, and their seeds remain among us. The Small Pox is now even not known in some parts of the world, but when once it is established, who can predict the period of its first appearance in an

epidemic form. The history of the disease informs us that in all the countries where it has been introduced, sooner or later an epidemic has seized the inhabitants.

A disease previously unknown in India appeared at Rangoon in the year 1824, which obtained the name of Scarlatina Rheumatica. Four years afterwards it attacked the Southern States of North America, and though the disease was so impartial as scarcely to spare a single individual of any town to which it extended its influence, it was not accompanied with that mortality which has usually been the characteristic of wide spread epidemics.

There is one peculiar feature of all epidemics which may be here mentioned as indicative of some definite, though at present unaccountable cause, operating in the sudden suppression of the disease after a certain period of duration. This distinctive character may almost be considered as a law in reference to these affections; if we take three distinct diseases, the Plague, the Irish Fever and the Cholera, we find the rule apply to all. Of the latter disease we have so recently been witnesses, that I need not quote authorities on this point concerning it. In Dr. Patrick Russell's work on the Plague at Aleppo I find the following remarkable passage. After alluding to the great increase of pestilential effluvia that there must be towards the close of an epidemic, compared with the amount at the onset of the disease, and expressing his

astonishment that so many escape infection, he says: "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." He then mentions that in Europe the sudden cessation may be partly attributable to the measures adopted for preventing its extension; but "at Aleppo, where the disease is left to run 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 interference of human aid, ceases entirely."

The expressions of Dr. Harty on this subject, in connexion with the Irish Fever, would apply as well to all other epidemics: "It is a fact, that though every diversity of management was resorted to for effecting the suppression of the disease, yet, nevertheless, there was an almost simultaneous and apparently spontaneous decline of the epidemic in the various and most remote parts of Ireland. It is not an easy matter to offer a satisfactory explanation of this circumstance, some general cause must no doubt have influenced the subsidence of the disease, yet that cause could not be atmospheric, inasmuch as the decline, though it might be said to be simultaneous, was not sufficiently so to admit of that explanation."

SECTION III.

THE DISPERSION OF PLANTS AND DISEASES.

The dispersion of Diseases and the dispersion of Plants, exhibit analogies which might be little expected, on a superficial view of the enquiry.

We are led to believe, that the earth as a whole, was not covered with vegetation in a day, the geological history of this planet is one of development, and though at first sight this expression of opinion may appear to savour of doubt in the Mosaic record, a more extended acquaintance with the subject, favours rather and confirms Scripture history.

As the peopling of the earth has been a gradual process with the animal creation, so has it been also with the vegetable kingdom. We see at the present day, that plants by various means of transit from place to place, multiply themselves on new soils and in new climes, the same with animals. By other means we observe, or can trace, the extinction from various localities and countries, of members of both the animal and vegetable kingdom.

We learn that originally this planet had a temperature much higher than at present, and that the variation of temperature between the equator and the poles, which we now witness, did not obtain in the earlier condition of the globe. We are given to understand, and not without considerable proof,

if not demonstration, that the earth was a vast bog, in which rank vegetation grew, and in which the ichthyosauri and plesiosauri, must have floundered about as unwieldy and loathsome bodies. We can readily conceive a condition of atmosphere at this time to have been loaded with pestiferous vapours of an organized nature; it is entirely in accordance with all we know, that it should have been so. Allied forms of plants to those now in existence, are found in the form of fossils, by which comparisons are made, but how the transition into the present Flora took place, or at what period, it is impossible to say. That these plants should have been entirely destroyed during the revolutions of the earth by earthquakes, and their consequences; the collection of waters into the vacuities formed, and their draining off from other places by elevations of the land, is not to be dwelt on without astonishment; then again the ultimate changes of temperature on the surface of the earth, may have been another element in the history of their extinction. But if we may be allowed to imagine that there were organic germs floating in the vapours of the atmosphere, these would hardly be subject to the same influences as those which depended solely on their fixation to the soil for subsistence. The atmosphere, their native element, being influenced by the commotions from below, would be agitated; vortiginous currents would be established, hurricanes would sweep over the stagnant pool and reeking morass,

and the higher regions of the air might have thus given protection to these subtle germs, while almost a total extinction of the elegant ferns, the stately palm, and the towering cane was in course of procedure. Then when the strife of the earth and elements had subsided, these would descend with the gentle breezes, and again find in various spots a local habitation—

"Where blue mists, through the unmoving atmosphere,

Scatter the seeds of pestilence and feed unnatural vegetation."

In the new era, when the earth took its present physiognomy, who shall say whether much of the pestiferous matter may not have been enclosed and condensed in the bowels of the earth, and when it is remembered, that earthquakes and convulsions of nature,[^[25]] have invariably preceded the outbreak of

any great pestilences, that stinking mists, coming from some unknown regions, and unusual vegetations have made their appearance in concert at these times, what I ask is more natural than to imagine, that they have been let loose during the general convulsion? It may be asked, what is to be said about that revolution of the earth, when the great Deluge spread over the whole face of the globe? It can only be replied, that this is a part of the scheme of cosmogony into which we are not called upon to enter. There are yet strenuous supporters of the partial as well as total submersion of this planet, but whether it be true that the vast torrents which appear to have swept the surface uniformly in a southern direction, were of a date coeval with the deluge, and constituted an essential portion of the phenomena, of which one was, that "the fountains of the great deep were broken up," or whether they were anterior to this catastrophe, will not at all interfere with the conjecture of a very early formation and propagation of the germs of pestilential diseases, for the commotions of a deluge were less likely to interfere with the vapours of the atmosphere, than extensive volcanic and electric disturbances. Moreover, it is rather in favour of this theory, that the

regions where the temperature and exhalations most nearly resemble those of the former condition of the earth, are those in which pestilential disorders most frequently arise, and where their virulence has always been most strongly marked.

After the various commotions which left the globe, with its present physiognomy of mountains, plains, valleys, rivers, lakes, and oceans; a new Flora and Fauna appeared to adorn and animate the scene of man's existence. Plants and animals were created apparently in adaptation to the numerous climes, which the seasons in the various latitudes or the elevations of the soil, were prepared to render fruitful and useful each in its own sphere. Besides this, the plants of the same latitude, in some instances, differ materially from each other; in this case it seems that the soil has much to do with this peculiarity, for it is certain that the soil and the contiguous atmosphere, have a close and intimate relation; the drought of the desert depends upon the sand, as humid atmosphere is connected with the morass. To illustrate the tendency which vegetation shews in appropriating one locality more than another, I may quote the following: "Some of the volcanic masses of the Æolian or Lipari Islands, that have existed beyond the reach of history, are still without a blade of verdure; while others in various parts, of little more than two hundred years date, bear spontaneous vegetation, and the same is seen on two lavas of Etna near each other, for the one

of 1536 is still black and arid, while that of 1636, is covered with oaks, fruit trees, and vines."

In comparing the diffusion of plants, and the diffusion of diseases, the different modes by which this generally has been effected may be considered under heads, that the comparison may be more readily traced.

First, seeds are diffused by the atmosphere, either by the prevalence of certain currents, which are produced by known laws, in which case, no difficulty occurs in the explanations; or in a more imperceptible manner, as by those more uncertain atmospheric currents of a partial nature, which, though they seem to have laws governing them, are not yet understood.

Second, seeds are transported by water across oceans, &c. when they can be floated on any material by which they are preserved, as by wrecks and masses of wood, which have been washed down the rivers.

Third, they are conveyed by man to all parts of the globe.

Fourth, a period of latency is observed to apply to them, that is, they require certain essential conditions before germination occurs; so that even in some localities, a plant may not have been known to exist in a particular neighbourhood, but by a train of circumstances, it may make its appearance, and again be a centre of development.

1st. I shall not here wander into the speculation,

whether plants had originally one birth-place, as a centre from which they spread by various agencies, as supposed by Linnæus, nor into any enquiry beyond those facts, which may fairly come within our own comprehension, and within our own means of demonstration.

Many seeds are provided with means adapting them for floating in the atmosphere, these are by pappi, or winglets and hairs, but it cannot be doubted that the agency of atmospheric currents, is productive of considerable effects in the dispersion of lighter seeds, such as those of mosses, fungi, and lichens—lichens have been discovered in Brittany, which are peculiar to Jamaica, and Monsieur De Candolle concludes, that their seeds had been carried thence by the south-westerly winds, which prevail during a great part of the year on this portion of the French coast.

But Humboldt's testimony on the subject of winds is most satisfactory, for he says, "Small singing birds, and even butterflies, are found at sea, at great distances from the coast (as I have several times had opportunities of observing in the Pacific), being carried there by the force of the wind, when storms come off the land." It is generally believed, from abundance of proofs, that the trade winds, and other continuous currents, are means by which plants are conveyed from one country to another.[^[26]]

As to the partial currents, Humboldt further says, "The heated crust of the earth occasions an ascending vertical current of air by which light bodies are borne upwards. M. Boussingault, and Don Mariano De Rivero, in ascending the summit of the Silla, one of the gneiss mountains of Caraccas, saw in the middle of the day, about noon, whitish shining bodies rise from the valley to the summit of the mountain, 5755 feet high, and then sink down towards the neighbouring sea coast. These movements continued uninterruptedly for the space of an hour. The whitish shining bodies proved to be small agglomerations of straws, or blades of grass, which were recognized by Professor Kunth, for a species of vilfa, a genus, which together with agrostis, is very abundant in the provinces of Caraccas and Cumana."

On the plague of locusts we read, that "the Lord brought an east wind upon the land, all that day and all that night, and when it was morning the east wind brought the locusts."

On the Black Death we read, "There were many locusts which had been blown into the sea by a hurricane, and a dense and awful fog was seen in the heavens, rising in the east, and descending upon Italy."

Of the Plague of 542, Gibbon says, "The winds might diffuse that subtle venom, but unless the atmosphere be previously disposed for its reception, the plague would soon expire in the cold or

temperate regions of the north. The disease alternately languished and revived, but it was not till a calamitous period of fifty-two years, that mankind recovered their health, or the air resumed its pure and salubrious quality."

In the history of the Sweating Sickness, of which there were five distinct visitations, we find ample allusions to the atmosphere, and the mode in which the disease was conveyed by this medium.

I quote again from Hecker: "It seemed that the banks of the Severn were the focus of the malady, and that from hence, a true impestation of the atmosphere, was diffused in every direction. Whithersoever the winds wafted the stinking mists, the inhabitants became infested with the sweating sickness. These poisonous clouds of mists were observed moving from place to place, with the disease in their train, affecting one town after another, and morning and evening spreading their nauseating insufferable stench. At greater distances, these clouds being dispersed by the wind, became gradually attenuated yet their dispersion set no bounds to the pestilence, and it was as if they had imparted to the lower strata of the atmosphere, a kind of ferment which went on engendering itself even without the presence of the thick misty vapour, and being received into men's lungs, produced the frightful disease everywhere."[^[27]]

Mr. K. B. Martin, harbour-master of Ramsgate, in a communication to Lord Carlisle on the Cholera of last autumn, says, "At midnight of the 31st August (1849), the Samson (steam-tug) proceeded to the Goodwin Sands, where the crew were employed under the Trinity agent, assisting in work carried on there by that corporation. While there, at 3 A.M. 1st September, a hot humid haze, with a bog-like smell, passed over them; and the greater number of the men there employed instantly felt a nausea. They were in two parties. One man at work on the sand was obliged to be carried to the boat; and before they reached the steam vessel at anchor, the cramps and spasm had supervened upon the vomitings; but here they found two of the party on board similarly affected. Here then is a very marked case without any known predisposing local cause. Doubtless it was atmospheric, and in the hot blast of pestilence which passed over them."

Many more instances might be quoted, to shew that the germs of disease, as well as of plants, are borne on the wings of the wind from place to place

in one country, and from one country to another, the distance being no obstacle, however great that may be.[^[28]] "Dust and sands," says Sharon Turner, "heavier than many seeds, are borne by the winds and clouds for several hundred miles across the atmosphere, falling on the earth and seas as they pass along." "The clouds not only bring us occasionally meteoric stones, hail, and epidemics, but also vegetable seeds."[^[29]]

2nd. The transportation of seeds of plants by water requires very little notice; every one is familiar with the mode in which coral islands, which gradually rise out of the sea, become covered with vegetation. "If new lands are formed, the organic forces are ever ready to cover the naked rock with life.—Lichens form the first covering of the barren

rocks, where afterwards lofty forest trees wave their airy summits. The successive growth of mosses, grasses, herbaceous plants and shrubs or bushes, occupies the intervening period of long but undetermined duration."

The following may be cited as an instance of the transportation of disease by water. "Cyprus lost almost all its inhabitants, and ships without crews were often seen in the Mediterranean, or afterwards in the North Sea, driving about, and spreading the plague wherever they went on shore."[^[30]]

It requires no argument to enforce the conviction that cottons, woollens, furs, skins, &c. will retain the matter of infection for almost an indefinite period; instances of the kind have been already given; it is therefore easy to understand that portions of wrecks and ship's goods would be a frequent though unsuspected source of infection. Dr. Halley mentions a case, in which a bale of cotton was put on shore at Bermuda by stealth; it lay above a month without prejudice, where it was hid, but when opened and distributed among the inhabitants, it produced such a contagion that the living scarce sufficed to bury the dead. Dr. Walker found seeds dropt accidentally into the sea in the West Indies cast ashore on the Hebrides. He says, "the sea and rivers waft more seed than sails." The waters of many rivers induce diarrhœa and dysentery.[^[31]] Well water also in many

places has a similar effect, especially if any surface drainage happens to find its way into the well.

3rd. The part performed by man himself in the communication of disease to his fellow creatures, is perhaps the most fruitful source of the extensive spread of epidemic and contagious diseases.

In the time of Moses, restrictions were laid on those who had the plague of the leprosy to avoid contagion; the dictum for one so affected was, "he shall dwell alone; without the camp shall his habitation be."[^[32]] All the ancient authors believed in the

infectious nature of pestilential fevers, and some other diseases; but, according. to Mr. Adams, they held that no specific virus was the cause, and merely a contamination of the surrounding air by effluvia from the sick. Thucydides, Hippocrates, Procopius, Galen, Plutarch, all recognized the property of communicability from one individual to another of the plague; and Hecker, on the epidemics of the middle ages, abounds with instances in support of contagion. As regards small-pox and measles, Rhazes observes particularly the connection that exists between the condition of the air and the severity or mildness of these diseases, remarking that small-pox seldom happens to old men, except in pestilential, putrid, and malignant constitutions of the air in which this disease is usually prevalent.

The history of the introduction of Scarlet Fever, Hooping Cough, Lues, and other diseases into the various countries of the globe, is sufficiently convincing that men carry about with them the seeds of disease; that while these attach themselves to the persons and clothing of those who introduce them into new climes, and flourish independently of cultivation, yet the exotics which they foster with so much care, often disappoint their most sanguine expectations; and these "languishing in our

hothouses can give but a very faint idea of the majestic vegetation of the tropical zone." Art in this procedure fails to accomplish here, what nature but too sadly, under some circumstances, effects most readily. The germs of some diseases though of an exotic character, under congenial influences of various kinds, appear to flourish with native vigour: is it not so, also, with some forms of vegetation? The aloe, a native of Mexico, which lives, but does not thrive well, or reproduce under ordinary circumstances in this country, will occasionally send forth a most luxuriant blossom;[^[33]] so rare is this, that some say it occurs every 50 or 100 years, but no law seems to be established on this point, any more than the statement that we may expect pestilential diseases at certain intervals. But that there are intervals of uncertain duration when the aloe will blossom, when the grapes will ripen, and a general productiveness of exotics will occur, is as certain as that seasons will occur when contagion will be rife, and a most unusual multiplication of disease prevail. This is not an imaginary or speculative notion,—all observers of seasons and diseases within the last twenty years, may fully verify the statement.

In 1846, a large vine, the black Hambro-grape,

ripened its fruit out of doors, and was as fine as any green-house production; but during nine years that the vine has been under my inspection, this was the only time I have witnessed such a result.

We are apt to attribute an abundant or scarce fruit season to temperature alone, but this is an error—for we have before remarked, that though certain lands may be in the same degree of latitude, the plants which thrive well on one land, will not do so on the other: in fine, that where reason and analogy would lead one to expect a particular form of vegetation, a totally different Flora is presented to the view. These facts are indeed suggestive of new and important deductions. Is it yet explained why the town of Birmingham should be free from Cholera? There is a large manufacturing population, a great number of poor, the usual overcrowding of individuals in small chambers, a considerable amount of destitution and depravity; irregular habits of living, and unwholesome diet, and doubtless many parts of the town, which on investigation would have yielded all the elements usually considered necessary for the localization of the disease: but no—here was some repelling cause, some opposing agent to the generation and propagation of the pestilential seeds. There are no known laws by which inorganic matter could be supposed to observe such a selection, or such an antagonism. Electricity, magnetism, ozone, gases, exhibit no such elective properties that here they will destroy, and

there they will spare; that they can almost depopulate small villages, and scarcely find a victim in Birmingham and Bath. But if we suppose a living, and multiplying matter as the cause of disease, many local causes may conspire to arrest the development of the germs, or perhaps, even utterly destroy them.

4th. As to the time of latency, facts crowd upon us indefinitely, as elements of comparison between vegetation generally, and disease in its early stages and history. The seeds of plants are extraordinarily tenacious of life. What a mysterious arrangement of the ultimate particles of matter must there be, by which the vital force remains apparently inactive for many years, and yet when the conditions arise favourable to its manifestation, as it were by an extraordinary fiat, life appears.

Previous to the year 1715, no broom grew in the King's Park, at Stirling; but in that year a camp was formed there, and the surface of the ground consequently was broken in many places. Wherever it was broken, broom sprang up. The plant was subsequently destroyed; but in 1745 a similar growth appeared after the ground had been again broken for a like purpose. Some time afterwards the park was ploughed up, and the broom became generally spread over it. "In several places in the neighbourhood of Edinburgh," says Professor Graham, "the breaking of the surface produces an abundant crop of Fumaria parviflora,

although the same plant had never before been observed in the neighbourhood. It is impossible to say the lapse of time since these were buried, before they were again excited to the performance of all their vital functions." Dr. Graham also gives another proof of the vital force existing in seeds. "To the westward of Stirling there is a large peat bog, a great part of which has been flooded away by raising water from the River Teith, and discharging it into the Forth,—the under soil of clay being then cultivated. The clergyman of the parish standing by while the workmen were forming a ditch in this clay, which had been covered with fourteen feet of peat earth, saw some seeds in the clay which was thrown out of the ditch; he took some of them up and sowed them: they germinated and produced a crop of Chrysanthemum septum. What a period of years must have elapsed while the seeds were getting their covering of clay, and while this clay became buried under fourteen feet of peat earth!"[^[34]]

What limit can there be to the dispersion of seeds when their vital properties may remain so long unimpaired? The seeds of which we have been speaking were, no doubt many of them, washed away with the waters of the Teith, and carried by the stream into the Forth; and who shall then mark their destination; for we have seen that by such means the most distant lands are supplied with vegetation; for whence come the plants which cover the Coral Islands, unless by the air and the water, and that both contribute, has been incontestably proved. Dr. Lindley states that melon seeds have been known to grow when forty-one years old; maize thirty years, rye forty years, the sensitive plant sixty years, kidney-beans a hundred years. But seeds in general have an indefinite period, apparently, at which they can retain their power of germination; for many of the seeds which had been kept in the herbarium of Tournefort for more than a century, were found to have preserved their fertility.

It has now to be shewn that the germs of disease also retain their vital powers in a state of dormancy during a lengthened period.