<*• =3, LIBRARY OF THE University of Prnnsylvama. THE STILLE LIBRARY. Class.EiYil(j.s. 17^ logical structure, state of cultivation, and distance from, or proximity to, large bodies of water. When all these circumstances are brought into one view, we might almost be persuaded, that they are capable of producing all the modifications of dis- ease which are seen in the ^ame and different coun- tries. That much must be attributed to those causes cannot be questioned, especially as certain disor- ders are extensively prevalent in some countries, which rarely or never appear in others. But if we advert to epidemic diseases, we shall find that those causes do not explain their origin, or account for all their varieties of character ; for the truth stated by Sydenham, that years perfectly agreeing as to the manifest temperature of the air, produce very different tribes of diseases, is applicable to every climate; and hence, to explain this fact, we must bring in the agency of epidemic meteoration. Admitting, then, that climate has a considerable in- fluence in producing and modifying diseases, the question recurs, whether the same kind of epidemic meteoration exists in different countries in which the same disease is prevalent ? A few general observa- tions on the several classes of epidemics, will serve to elucidate this subject. 1. The most remarkable varieties of insensible meteoration are those which immediately produce epidemics. Now as these varieties are the efficient causes of disease, it follows of course, that they are always alike in every country, where the same mete' orations epidemics appear, and that the modifications of 23 17o l>j±jLO>OPili these several diseases must arise from the influence of local causes. For example, influenza, which is the best instance of a meteoratious epidemic, some- times pervades a vast extent of country. In all places, it exhibits the saiiK'. general character, whence it is evident, that its cause is the same in every situation, and that its modifications in differ- ent districts are produced by the diversities of locality and climate. The epidemic meteoration which produced the Pneumonia Typhoides, in the northern parts of the United States in 1812—13, probably did not essen- tially differ in its qualities in any of the districts in which the disease prevailed, notwithstanding in some places it manifested a more asthenic and ma- lignant character than in others. The opinion of Dr. Hosack, in relation to this complaint, is undoubt- edly correct. Presuming its epidemic cause to be the same in every situation, he says, "typhoid pneumonia is materially modified by locality, as is evident from the best accounts, furnished by the most respectable American practitioners, who have recently witnessed its ravages in various parts of the United States."* Similar facts are recorded by Huxham. "I have once and again taken notice," says he, " that an epidemic disorder, which in low, warm places near the sea, proved only a catarrhal fever, and scarce required any manner of bleeding, hath, in the neighbouring cold and high * Practical Nosology, p. 205, note, Edit. 2d. OF EPIDEMICS. 17* exposures, been attended with severe pleuro-peri- pneumonic symptoms, and demanded no small evacuation of blood." That Huxham considered the epidemic meteoration, from which the disease originated, to be the same in every place where it prevailed, is evident from his observations which follow the passage just cited.* But although every atmospheric epidemic, which is characterized by the same pathognomonic symp- toms, manifestly depends upon an identity of cause, yet it is probable, that the same kind of epidemic meteoration may act on the system with greater intensity in some situations than in others. Thus on the borders of its range, where it runs into another variety of insensible meteoration, its effects may be slightly felt; moreover, its force of action may vary, in degree, at the same time in different places, according as its epidemic opera- tions may be commencing, progressing, or termi- nating therein ; for it is frequently observed, that meteoratious diseases gradually extend from one country to another, without differing in their nature, though often diminished or increased in violence. 2. If we now turn to those varieties of epidemic meteoration, which, instead of producing diseases peculiar to themselves, are principally operative in favouring the prevalence of contagious distempers, we shall meet with a different view of the sub- feet. * Spe bis Essay on Fevers, p. 258. Edit. 3d. ISO PHILOSOPHY The contagions of small-pox, measles, and othei communicable febrile disorders, are severally of the same nature in all countries ; and consequently, their diseases would always present the same ap- pearances, were the constitutions of individuals alike, and the modifying influences of infection and meteoration always the same. But this is far other- wise. Contagious epidemics are not only modified by infection, but are varied in character by climate, and especially by epidemic meteoration. • If, then, it be supposed, that small-pox or measles is epidemic in places distant from each other, for instance, in New-York and London, the inquiry arises whether the epidemic meteoration which favours its prevalence, is of the same kind in both places ? or whether different forms of it exist in those remote regions ? In order to answer this inquiry, it is necessary to advert to the modifications of con- tagious epidemics which appear in the same city. In some years, they are observed to be much mgrot inflammatory and mahgnant than in others ; or, to use the terms of Sydenham, as applied to small- pox, they are sometimes mild and regular, and at other times irregular and anomalous. In some vari- olous epidemics, one-third of those affected in the natural way die of the disease, while in others, the mortality is scarcely one in fifty. As these discre- pancies cannot be entirely ascribed to the varying influences of climate, or to the sensible qualities of the air, it is evident, that several and very different varieties of epidemic meteoration predispose the OF EPIDEMICS. 181 system to contagious distempers, and favour their propagation. The application of these facts to the question of small-pox or measles, in New-York and London, will enable us to solve it with accuracy. If the disease be mild in the former city, and malignant in the latter, or vice versa, (the influence of infection aside) the conclusion follows, that the epidemic meteoration is different in the two places,—but, should the phenomena of the disease correspond in both cities, that it is the same. Such variations, in the charac- ter of contagious epidemics, do undoubtedly often occur in various and distant countries. 3. Phenomena analagous to those noticed above are frequently observed in infectious epidemics. The character of yellow fever and other koino miasmal diseases, is, mdependently of the effects of locality and climate, remarkably influenced by the varieties of epidemic meteoration, m the same and different seasons and places. First, with regard to the same place in different seasons. The yellow fever of Philadelphia, in 1793, admitted of copious depletion; whereas in 1803, moderate bleeding was sufficient to subdue the disorder. Dr. Rush tells us, that "the dis- ease assumed a new character this year, and was cured by a different force of medicine from that which was employed in some orthe years in which it had prevailed in Philadelphia."—" The difference in the violence and mortality of the fever," he thinks, " was probably occasioned by a less con- 132 PHILOSOPHY centrated state of the miasmata which produced it, or by the co-operation of a less inflammatory constitu- tion of the atmosphere"* To the latter of these causes, we are inclined to ascribe the compara- tively mild character of the disease ; for we know of no facts which prove that the action of perkoino miasma, when it prevails epidemically, is ever mate- rially lessened in force on account of " being in a less concentrated state." Secondly, with respect to different places in the same season. The documents relating to the yellow fever, as it appeared in New-York and New- Orleans in the year 1819, clearly evince, that the epidemic meteoration which prevailed in the two cities, was strikingly dissimilar. We are told, that in the disease at New-York, "the alarming debility and the exhausted state of the vital powers, forbade the employment of the lancet ;"f while at New- Orleans, it is said that " venesection, when resorted to early, promptly, and fully, was most beneficial, and obtained at least a temporary mitigation of the symptoms, reheving for the tjme, the excruciating pains, and restoring disordered intellect;" and fur- ther, that " all the cases that terminated favourably were bled freely."t The same kind of insensible meteoration appears to have prevailed in New- Orleans during the^pidemic of the following year, * Medical Inquiries and Observations. t New-York Med. Repository, N. S. vol. vi. p. 125. | New-York Med. Repository, N. S. vol. vi. p. 11, 12. OF EPIDEMICS. 183 for it is stated that " bloodletting was generally indi- cated in the first stage of the disease, and in most cases, was carried to a very great extent with the happiest effects."* The proximity of New-Orleans to the torrid zone, and the northern situation of New-York, for- bid the supposition, that the opposite diatheses of the yellow fever in those cities in 1819 were entirely owing to a difference of chmate. If this cause were capable of producing such effects, should we not suppose that the fever would have been more inflammatory or sthenic in the latter city than in the former. That this would have been the case seems evident from the fact, that cold climates produce a denser fibre, and a condition of body which admits of larger detractions of blood than that state of the system which commonly pre- vails in hot climates. But in some years it happens, that yellow fever exhibits the same meteoratious modification, both in southern and northern coun- tries, and again, in other years, it is marked by high sthenic action in the latter, and adynamic symptoms in the forhier. In like manner, the character of plague, remit- tent and intermittent fevers, and even typhus, is often diversified by different kinds of epidemic mete- oration. Sometimes, these maladies call for free depletion in their early stages ; whereas, at other * Report of the Committee of the Physico-Medical Society of New-Orleans, on the Epidemic of 1820, iai PHILOSOPHY times, the}* do not admit of the use of the lancet * Besides, there is frequently a remarkable tendencjr in autumnal fevers, to concentrate their force on particular organs. Thus, in one epidemic, the onus of disease falls on the head, and in another, on the stomach or bowels. Dysentery affords a striking example of a modified febrile disorder; it is usually, as we have said before, a miasmal fever, which is changed to the dysenteric form by a peculiar variety of epidemic meteoration. We have been the more anxious to draw a line of distinction between the influences of climate, and of epidemic meteoration, on account of its prac- tical importance. It has been shown that climate varies the character of diseases, but that it is in- capable of producing all the modifications of con- tagious and infectious epidemics; and hence we perceive the necessity of studying the diseases of particular countries, and of particular seasons. The physician, who is conversant with one climate only, is incompetent to discharge his professional duties with correctness in another. It is on this ground, that American physicians insist that the medical writers of Europe are not able to en- lighten them on the nature and character of the epidemic diseases of the United States. But another reason, why the physicians of one country should not be governed by the precepts of those who describe the epidemics of another, is, the in- sensible meteoration, prevailing in districts remote from each other during the same epidemic, may be OF EPIDEMICS. 18,5 different, and consequently, the practice must vary accordingly. That much light, however, can be shed on the nature and laws of epidemics by inves- tigating the phenomena they exhibit in different parts of the world, cannot be questioned; but to treat them successfully, the remedies must be adapted to the climate and the variety of epidemic meteoration under which they appear. Before closing our observations on the varieties of epidemic meteoration, it is proper to remark, that such of them as promote the spread of contagious diseases are generally unfavourable to the preva- lence of infectious fevers, and vice versa. It is said by Sydenham, that " as many of these diseases (epidemics) appear in the same year, some one or other of them rules over the rest, which rage less at the same time; so that this one increasing, the others decrease, and this diminishing, the others soon re-appear." This proposition is intended to ex- press a general law of epidemics ; but as it is here stftf&d, it is neither sufficiently explicit, nor properly qualified. As every epidemic depends either directly or indirectly on insensible meteoration, and as no two varieties of it can exist together, it is obvious, that two epidemics of equal power cannot prevail at the same time and place. But still, among the great number of varieties of insensible meteoration, there are, no doubt, some which are more or less fa- vourable to the prevalence of several kinds of epi- 24 I8tf PHILOSOPHY demic diseases. Thus, some of those varieties may not only immediately produce disease, but favour the ravages of contagious or infectious dis- orders, and especially of the former; indeed, the primitive affinities which have been shown to exist between meteoratious and contagious epidemics, as well as the history of these diseases, seem to prove that certain states of the atmosphere are sometimes particularly favourable to their simultaneous preva- lence. But, though further observation and research are necessary to a complete exposition of this subject, in general, it may be said, that when a well defined meteoratious epidemic is raging, for example, influ- enza, contagious and infectious disorders rarely or never prevail to any considerable extent. So also, when the atmosphere favours the prevalence of an infectious fever, no other disease ordinarily appears as an epidemic, yet such as do occur will be more or less assimilated to the character of the reigning malady. Thus far the observation of Sydeiflrtrhi may be regarded as strictly correct, that " as many disorders appear in the same year, some one or other of them rules over the rest." But the slight- est reflection will render it evident, that this law is not applicable to contagious epidemics ; for in no instance can they be said to rule over other com- plaints. They hold a subordinate station in the catalogue of general diseases; and though their propagation is favoured by insensible meteoration, yet as they cannot contaminate the air generally, OF EPIDEMICS. 187 they can have no assimilating control over other disorders. It sometimes happens, indeed, that there are more cases ^rf a contagious disease in a city or country-town than of any other malady; and hence it was that Sydenham thought that small- pox and measles sometimes ruled over the disor- ders which " rage less at the same time." As we have already shown the fallacy of this doctrine, we have now only to remark, that the insensible mete- oration, which favours the prevalence of contagious epidemics, is operative on all the diseases which appear at the time, and to the character of these, however small be the number of cases, the prevail- ing contagious disorders will be more or less as- similated. Thus, according to Sydenham himself, " when the small-pox prevails, the fever of that year, which is less general, plainly partakes of the same inflammatory nature therewith." If any circumstance more than another distin- guish the truly Hippocratic physician, it is the dili- gence with which he studies the operations of epi- demic meteoration on the prevailing diseases. He who disregards or overlooks this plastic energy of the atmosphere, and directs his attention solely to the vicissitudes of the weather, and the changes of the seasons, can have but a partial view of the agencies concerned in the production of diseases ; and must frequently be in danger of committing errors in practice. Mr. Webster judiciously re- marks, in speaking of Sydenham, that " his occult qualities have been ridiculed by later physicians, 188 PHILOSOPHY OF EPIDEMICS. and so far as his theory, in this respect, has been neg- lected, the science of medicine has degenerated." And he pertinently adds, 4hat " if I mistake not, it can be made evident, that one of the most impor- tant, as well as most difficult branches of medical science, is to ascertain the effect of the reigning constitution of air on the prevailing diseases, and to apply that knowledge to the cure of those dis- eases." * History of Epidemic Diseases, vol. i. p. 15. SECTION V. INQUIRY WHETHER EPIDEMICS OCCUR IN A DETER- MINATE ORDER. "Whether a careful examination, such perhaps as could not be made in the life of one man," says Sydenham, " might show that certain tribes of epi- demic disorders constantly follow others in one deter- minate series, or circle, as it were ; or whether they return indiscriminately, and without any order, ac- cording to the secret disposition of the air, and the inexplicable succession of seasons, I am not cer- tain." And again, he remarks, " the thing I en- deavour is to show, by the assistance of a few years' observations, how this matter stood lately with respect to my own country, and the city wherein I five; in order to assist in beginning a work that, in my judgment, will greatly tend to the advantage of mankind, when at length it shall be finished by posterity, and the whole series of epi- demics be exhibited to view, as they shall succeed each other for the future."* The superior discernment and unwearied zeal * Works, page 4, 12, 190 PHILOSOPHY of Sydenham, in his medical pursuits, enabled him to accomplish more towards elucidating the laws and phenomena of epidemics than any who had preceded him. His pages, however, afford the clearest evidence that he frequently erred in his etiology of diseases. Believing that epidemics were generally produced by constitutions of the at- mosphere, he naturally indulged the idea that those constitutions might revolve in a circle, giving rise to a determinate series of epidemics. This idea would still be worthy of regard, were we to look to no other causes of epidemics than meteoration. But modern researches, and a sound- er philosophy, have extended the boundaries of etiology. It is now generally admitted, that a ma- jority of epidemics do not owe their origin imme- diately to the " constitutions" of the air ; but to other sources, namely, contagion, the offspring of morbid animal secretion, and infection, the produc- tion of animal and vegetable putrefaction. Had Sydenham possessed clear and distinct notions of these causes of disease, and bestowed that atten- tion to them which he gave to epidemic meteora- tion, he doubtless would have more largely contri- buted to the advancement of this department of science. He would have seen that the prevalence of contagious and infectious diseases is in a mea- sure contingent; and consequently, that they could not enter with uniformity into a determinate series of epidemics. OF EPIDEMICS. 191 Our distinguished countryman, Mr. Webster, has been at much pains to ascertain the order and progression of epidemic diseases. He has endea- voured to show that there is a natural connexion between the occurrence of earthquakes, the ap- pearance of comets, and the ravages of pestilence. He says, that " every epidemic constitution seems to commence with measles or influenza. To these succeed angina, in some of its various forms, which are all the offspring of the same parent. Then follow pestilential fevers, in the form of dysentery, yellow fever, and plague."* This industrious writer has assembled a multi- tude of examples to prove the above order and progression of epidemics. But the reader will perceive, at a glance, that he has arranged diseases together, which have no specific affinities, as measles, which is propagated by contagion, influ- enza, and angina, which originate from meteoration, and dysentery, yellow fever and plague, which de- pend on infection. If the history and causes of these disorders be carefully investigated, it will ap- pear that their occurrence in the order he has enu- merated them, will by no means certainly happen; but, on the contrary, may frequently be very differ- ent. It is true, the changes of the seasons intro- duce new diseases, and in this way only can cer- tain disorders be said to succeed each other with * History of Epidemic and Pestilential Diseases, vol. ii. p. 35. 192 PHILOSOPHY regularity. But this is not the order he contends for; he distinctly alludes to " epidemic constitu- tions," and we cannot wonder that he should have fallen into error, when we consider the data from which he has deduced his conclusion. He has tra- velled over a large portion of the earth, in order to gather facts suited to his purpose; and having brought them together, finds no difficulty in redu- cing epidemics into a determinate series. In one year, for instance, he finds influenza or measles prevalent in different countries ; in the next year, angina in a particular town ; in the next, dysentery, plague, and yellow fever, in various and distant regions, and so from year to year, different diseases in different places, thus making out his succession of epidemics from the four quarters of the globe. This mode of reasoning is palpably illogical, and it is singular that the author did not see its fallacy. If such reasoning be admissible, it would not be difficult to establish any order of epidemics, which the imagination might suggest. We would not be considered as intending to disparage, or undervalue the medical writings of Mr. Webster. His endea- vours to elucidate the causes and philosophy of epidemics have unquestionably tended to advance our knowledge of this intricate branch of science, notwithstanding, in some of his reasonings, he has not adhered to the rules of medical logic. If we turn to the medical annals of different countries, we shall scarcely find any two of them OF EPIDEMICS. 193 agreeing as to the succession of epidemics:—on the contrary, it will appear, that the popular dis- eases of one country rarely correspond with those of another. Take for example, Great Britain and Egypt, Buenos Ayres and New-York, or take pla- ces less remote from each other, compare the order of the epidemics which have prevailed in each for any number of years, and the result will afford incontestable evidence of the truth of the above remark. Sydenham, to whom belongs the merit of beginning the work of ascertaining whether epide- mics follow each other in a determinate order, con- fined his views to his own country, and the city where- in he lived; and in doing so, pursued the only proper method of solving the matter in question. The supposition that epidemics do occur in a de- terminate series, but in a different order in different countries, leads the mind to contemplate the inter- minable labour of investigating the immense variety of epidemic revolutions throughout the world, which collectively would form a grand cycle of epidemics. But such a task, it is believed, is not im- posed on the medical philosopher. From the facts already accumulated, we may legitimately conclude, that epidemics not only follow each other in a different order in various countries, but also in the same place. To calculate the future from the past is a favour- ite pursuit of the human mind. The civilian is no less curious in his speculations relative to the politi- 25 194 PHILOSOPHY cal destinies of man, than is the physician with respect to the future occurrence of epidemics. The influence and policy of the former are well known to have some agency in determining the fortunes of a nation; but how futile are his attempts to predict the order of successive revolutions in mind and empire: the prophetic labours of the latter, must, if possible, prove still more nugatory, seeing he has no control over the secret and desul- tory changes which are constantly going on in the air he breathes, and which constitute the varieties of epidemic meteoration. We cheerfully admit, however, that those insalutary states of the atmos- phere, which have repeatedly occurred in every age, may occur again, and consequently, that past epi- demics may be expected to return. There are, indeed, phenomena which indicate the approach of certain epidemic diseases ; but until those pheno- mena appear, no former observation will enable us to foretell the occurrence of such diseases, much less to determine their order and progression. The proper method, therefore, of studying the philosophy of epidemics, is to devote particular attention to their causes, and the signs which are premonitory of their appearance. Were this method strictly pursued, as much benefit would accrue from it, as if it were true, and the fact well known, that epidemics recurred in a stated order, having indefinite periods of time between them; for even then, attention to their prognostic signs would be equally necessary. OF EPIDEMICS. 19B By arranging epidemics into three classes, ac- cording to their remote causes, we separate those diseases over whose prevalence we have a limited control, from those which no human means can avert. Of the former kind, are contagious and infectious disorders, and of the latter, such as are meteoratious. This arrangement enables us to pro- nounce, in general terms, the important truth, that the prevalence of two distinct and well marked classes of epidemics, is, in a degree, fortuitous— a fact that puts for ever at rest the question, whether they succeed each other in a determinate order ? The universal adoption of vaccination has well nigh dispelled the terrors occasioned by the most fatal and loathsome disease in the catalogue of con- tagious epidemics; and though the other disorders of this class frequently appear, their prevalence may be checked by separating the well from the sick. Infectious epidemics are in a considerable mea- sure dependent on the localities of a country; and in some situations, their appearance is, for the most part, casual; thus, if animal and vegetable substan- ces are suffered to accumulate and putrefy in the streets and enclosures of a city or country-town, the effluvia exhaled from those substances will or- dinarily produce an infectious fever, which will cer- tainly become extensively prevalent, if favoured by epidemic meteoration. Now this maybe-avoided 19G PHILOSOPHY by attention to public cleanliness, and the removal of every source of noxious exhalations. Marshy and low countries are less under the do- minion of a medical police; but in many instances, their insalubrity may be corrected by draining, cul- tivation, or extensive and continued inundation. Empedocles is said to have removed an infectious epidemic, by turning two streams of pure water into the stagnant river Selinus, the exhalations from which produced the disease. Such expedients have frequently, under every variety of epidemic meteoration, prevented the occurrence of infectious diseases. Europe enjoys, at present, a compara- tive exemption from the pestilential epidemics which formerly desolated that quarter of the world,—an exemption which is justly attributed to improvements in agriculture, the arts, and municipal economy. In a word, to render an infectious fever general through a town or section of country, there must be a concurrence of so many circumstances, both of an accidental and unavoidable nature, that, in common, it is easier to prevent the genera- tion of miasmata, than it is to foresee when such a concurrence will happen. Although it is obvious that the prevalence of contagious and infectious disorders is in a manner contingent, and of course, can take no place in a determined series of epidemics, it may still be ques- tioned whether meteoratious diseases do not occur in a particular order? or, to make the question OF EPIDEMICS. 197 more general, whether insensible meteoration does not go through a determinate routine of modifi- cations, at one time producing epidemics, and at other times favouring the successive prevalence of contagious and infectious diseases ? However this may be, we know of no facts in support of the affirmative ; the history of meteoratious, as well as other epidemics, obviously leads to a conclusion directly opposite. SECTION VI. INQUIRY HOW FAR EPIDEMICS ARE CONNECTED WITH EXTRAORDINARY SEASONS, FAMINE, UNWHOLE- SOME FOOD, AND DISEASES AMONG BRUTES. r We formerly remarked, that the United States afforded a wide field for the cultivation of etiological science. Here, the causes of epidemics occur in their simplest combinations : and although we are unable to trace minutely the manner in which they are generated, yet it may be affirmed, that many of the circumstances which are enume- rated by some European writers, as efficient causes of pestilence, are not necessary to its production. Thus we know that excessive crowding in cities, extraordinary seasons, as to their sensible effects on the constitution, famine, unwholesome food, and nakedness, are none of them essential to the rise and prevalence of infectious epidemics, except that produced by idio-koino miasma, which does, indeed, require domestic filth and crowding. The discovery of what is, and what is not essen- tial to the existence of an epidemic, is an important acquisition to medical science; and with this know- ledge, we are led to regard the circumstances PHILOSOPHY OF EPIDEMICS. 199 just mentioned as having a subsidiary, but never an essential influence in producing pestilential or other epidemic diseases. In this country, as in every other, contagious epi- demics depend on their respective poisons, and a favouring insensible meteoration. Our infectious epidemics, as well those which originate from per- koino miasma as from prntnkninn miasma, frequently occur in situations where crowding, famine, un- wholesome food, and nakedness have no agency in their production. We therefore attribute them to miasmal poisons, engendered in the soil. They affect those who with temperance enjoy all the luxuries of life, though not perhaps in an equal degree with those who experience the evils of improvidence, or waste their energies in habits of sensuality. Epidemics arising from idio-koino miasma are probably often connected with the want of food and comfortable clothing. They generally occur in the lowest ranks of society, and in crowded camps. But that the privation of sub- stantial food is not necessary to their occurrence, might be shown by numerous examples, where their victims have been well and abundantly fed. As to meteoratious epidemics, they are obviously produced by some morbid quality of the atmosphere, inde- pendently of the individual and social conditions of men. These observations are premised in order to show that those writers who have ascribed certain 200 PHILOSOPHY epidemics to a multitude of morbid influences, slowly advancing and concentrating their forces to a point, at which they become pestilential, have not discriminated with sufficient care between the essential causes of epidemics, and those circumstan- ces which at most are only accessory sources of disease. But let us examine the several topics embraced in this section, according to the rules of analytical research. 1. What influence have extraordinary seasons in originating Epidemics? We are told that pestilence has frequently appear- ed after long and severe winters; and that other unusual seasons have been followed by epidemic disorders. Lord Bacon and some others have en- deavoured to deduce from such observations, a series of prognostics relative to the appearance of subsequent diseases. But the exceptions to all of them are so numerous, and the peculiarities of the seasons so opposite, in regard to the prevalence of the same disease, that their value is in a great measure, if not entirely destroyed. When it is said that a sickly season follows an unusually frosty winter, or that " great droughts in summer, lasting till towards the end of August, and some gentle showers upon them, and then some dry weather again, do portend a pestilent summer the year following;" or that " a dry March and a dry May portend a wholesome summer, if there be a showery April between; but otherwise, it is OF EPIDEMICS. 201 the sign of a pestilential year ;"* we perceive that these prognostics are at most but plausible conjec- tures. That pestilence has followed such seasons no one will question, but that this sequence will always, or even generally happen, is contradicted by long experience. The prediction that one year will be sickly, and another healthy, can have no reference to the particular kinds of epidemic dis- eases, which will appear, for these arise from dis- tinct causes, and are all of them regulated in their occurrence by the varieties of epidemic meteora- tion. But, in further discoursing on this subject. let us pursue the order of the seasons. In every winter, whether rigorous or mild, the general diseases are either contagious or meteora- tious ; for koino miasma is always extinct at this season. Now what are the prevailing diseases ? Are they contagious or meteoratious, or do both kinds exist at the same time, governed by the law of assimilation, formerly illustrated ? The answer to these questions may be given in the reply to another ; namely, what is the prevailing epidemic meteoration ? That this cannot be determined by the sensible qualities of the air is evident, since we know that different epidemics occur in winters which, in all respects, are apparently similar. Thus in one winter, the insensible meteoration favours the prevalence of small-pox, measles, or some other contagious disorders, and in another, produces * Bacon, as quoted by Hancock 2fi 202 PHILOSOPHY a distinct meteoratious epidemic. If, therefore, we are unable to determine what kind of epidemic will occur, under known circumstances of the weather in winter, it is obviously impossible to pre- dict, whether a severe or mild winter will introduce a contagious, infectious, or meteoratious epidemic in the following summer and autumn. As we have no data except the sensible quahties of the air by which we can judge of the future, and as the suc- cession of the varieties of epidemic meteoration is irregular, it is not within the reach of human pene- tration to foresee what species of epidemics will appear in any future season. A mild or frosty winter, or one remarkable for vicissitudes, has, so far as can be discovered, no agency in determining the kind of epidemic mete- oration which prevails at the time. If, at this sea- son, a meteoratious disease be epidemic, the altera- tions of temperature will operate as exciting causes, and thereby multiply the cases of the reigning dis- ease. Hence it is, that the same kind of epidemic meteoration, prevailing in winters unlike each other in regard to the sensible qualities of the air, very materially differs in the extent of its ravages. For example, when the weather is uniform and favour- able to health, the disease is not excited in so large a number of persons as when its changes are sud- den and frequent. In attempting, therefore, to determine whether an approaching season will be healthy or otherwise, we should not presume, in the present state of OF EPIDEMICS. 203 science, to foretell what species of epidemic will occur; but if it can be predicted, what kind of sen- sible meteoration will prevail, it will not be difficult to calculate its effects in exciting disease and pro- moting the generation of infectious effluvia. An intemperate and variable spring, whatever may have been the character of the preceding winter, will not be remarkable for sickness, unless an epi- demic meteoration exist at the same time; and accordingly, if in winter, we undertake to prognos- ticate the kind of sensible meteoration which will prevail in the following spring, with a view to pro- nounce upon the healthiness or unhealthiness of the season, it should be done under a distinct^ expression of the contingency just mentioned. As* to the contagious eruptive fevers, sensible meteora- tion has no influence in favouring, or suppressing their prevalence, for they prevail in all seasons of the year; and consequently, it is impossible to pre- dict any thing relative to their epidemic appearance. Our calculations respecting the kind of epidemic which will occur in an approaching summer and autumn, must also terminate in uncertainty. But if we can foresee the peculiarity of the sensible meteoration which will prevail, we shall have the best, and indeed, the only data meteorology affords, from which a correct judgment can be formed in regard to the salubrity of the season. Sensible meteoration, in the summer and autumn, is well known to act directly and indirectly in pro- ducing disease; directly in causing functional 204 PHILOSOPHY derangements, and exciting disease, and indirect!} in promoting the generation of infectious miasmata. Now should the weather be warm, moist, and calm, and the wind southerly, we may expect, that in marshy and filthy situations, miasmata will be pro- duced, and that fevers will be the consequence ; but their form, diathesis, and extent of prevalence, will depend on the concurring insensible meteora- tion. Should this prove favourable to the occur- rence of an infectious epidemic, the miasmata will obviously be the predominating morbid influence. A contagious or meteoratious epidemic, however, may appear in the warm months, and in this case, tjfcie epidemic meteoration will be unfavourable to the ravages of miasmal diseases. To render a prognostic worthy of confidence, it should be founded on principles which are uniform in their operation. Now none of the prognostics of pestilence are founded on such principles ; for there are no phenomena in one season, which are uniformly followed by peculiar phenomena in the succeeding one. Hitherto, the predictions of phi- losophers, so far as we are acquainted with them, have had an exclusive relation to the diseases which occur in one part of the year. They prognosticate from the weather of the winter and spring, that pestilence will prevail in the following summer and autumn; but never undertake to predict the epi- demics of winter, by meteorological observations made in the preceding summer and autumn. If the latter is impossible, is not the former equally so? OF EPIDEMICS. 205 From these observations, we are induced to be- lieve, that our knowledge on this subject may be summed up in a few words. In summer, we may safely affirm, that koino miasmal diseases will not prevail in the following winter; and that the dis- orders in this season will be contagious or meteora- tious, or both ; but what particular diseases will appear, must remain a matter of conjecture. And again, in winter, we may assert, that infectious diseases will occur in the succeeding summer ; but whether these, or. contagious or meteoratious distempers will prevail extensively, must also remain problematical. In our predictions from the signs of the weather, therefore, we should limit our views to the kind of sensible meteoration which will prevail in an approaching season. If this can be correctly prognosticated, our knowledge of its modus operandi will readily enable us to determine what effect it will have on the public health. But does not the influence of one season on the system leave a predisposition to disease the next ? On this point, there can be no doubt. The tonic operation of the cold of winter, and the relax- ing influence of the heat of summer, render the system particularly hable to disease whenever the seasons change. The effects of these annual varia- tions of temperature are, in general, well under- stood ; and it is only necessary to advert to them to show that they have no connexion with epidemics. They are the uniform consequences of those peri- odical alterations of sensible meteoration, which 206 PHILOSOPHY constitute the revolution of the seasons. The predisposition, induced by the long continued operation of heat or cold, therefore, cannot be considered an epidemic predisposition, but an effect regular in its occurrence, though variable in force in different years. In most countries, the seasons change progres- sively, and the system varies its condition in a cor- responding manner, following the transitions for the most part, pari passu. Johnson remarks, that " a cold winter succeeding a hot autumn, or a hot sum- mer succeeding a cold spring, will render the usual diseases of the seasons infinitely more severe."* When such effects occur, we might easily be led to suppose, that they depend on an epidemic state of the atmosphere, whereas, the fact is, they are, as Johnson correctly observes, the usual diseases of the season, which are rendered more severe, and of course, they can have no essential connexion with epidemic meteoration. Should an epidemic condition of the atmosphere, however, concur with such ex- traordinary variations of sensible meteoration, the most serious consequences will follow. The opinion of Sydenham on the disorders in question, will form an appropriate conclusion to this division of our subject. Amidst all the difficul- ties which impeded his progress in the study of epidemics, he clearly perceived that a distinction should be made between the disorders which arise from sensible meteoration, and such as proceed from * Practical Treatise on Derangements of the Liver, &c. p. 5. OF EPIDEMICS. 20? the occult quahties of the air; and accordingly, he distinguished them by specific epithets. The dis- eases produced by the former he called intercurrent, and those arising from the latter stationary. " The fevers," he says, "that appear in all years (which we therefore call intercurrents) do proceed from , some one or other manifest quality of the air; for instance, pleurisies, quinsies, and the like, which generally happen when an intense and long con- tinued cold is immediately succeeded by a sudden heat. It may therefore be, that the sensible quali- ties of the air have some share in producing those intercurrent fevers, which appear in every constitu- tion of the atmosphere, but they do not cause the epidemics pecuhar to the general constitution. And yet, at the same time, it must be acknowledged, that the above mentioned quahties of the air may more or less dispose the body to the particular epi- demic disease ; and the same may be affirmed of any error in the non-naturals."* 2. In what manner are famine and unwholesome food connected with Epidemics ? Famine is sometimes partially experienced in countries in which there is not an absolute deficiency of provisions. In such cases, it is confined to the poor; and is owing, either to their habitual indo- lence, or to their employment being interrupted by the suspension or derangement of commerce and manufactures. Famine may also occur in cities, under protracted sieges, or in consequence of the * Works, page 5. 208 PHILOSOPHY miscarriage of naval and military enterprises, whereby supplies are cut off, or not received in season. Allied to the calamity experienced on such occasions, is the necessity of subsisting on food of an unwholesome quality, an evil which is frequently experienced in armies and on board of ships. These several causes of famine have no natural connexion with the efficient causes of epi- demics. They are altogether incidental; though their effects are evidently calculated to predispose to disease, and to aggravate an epidemic with which they may happen to be coincident. But the causes of famine to be most dreaded, are those which occasion a positive and general deficiency of the means of subsistence, as when the earth does not yield its fruits in their wonted quantities, or when they are destroyed by preda- tory insects. As the causes here alluded to depend on natural occurrences, no human agency can entirely avert or control them. The concurrence of famine from physical causes, with epidemic diseases, has been noticed from the earliest ages; and there is reason to beheve, that their association is not accidental; but that it arises from their dependence upon similar atmospheric phenomena; and hence it is con- sidered, that famine is never the primary and effi- cient cause of epidemics. The causes of famine, however, are not equally attendant on the several kinds of epidemics. Con- tagious and meteoratious diseases prevail in every OF EPIDEMICS. 209 season of the year, and consequently their causes cannot be always identified with the peculiar mete- oration that blights the fields, and destroys the hopes of the husbandman. It is therefore chiefly with infectious epidemics, which occur exclusively in the summer and autumn, that the causes of famine are found to be coincident. It has already been stated, that there are varieties of epidemic meteoration, which favour the preva- lence of infectious diseases. This fact will now en- able us to explain how it happens, that infectious epi- demics are sometimes accompanied by disease in the vegetable kingdom, and not at other times. Some of these varieties not only promote the generation of koino miasma, but induce a sickly disposition in vegetables, frequently impairing their fruits, and sometimes destroying them. Dr. Rush observes of the pestilential season of 1798, a year memo- rable in the United States, on account of the ravages of the yellow fever, " that peaches ripened this season three weeks sooner than in ordinary summers, and apples rotted much sooner than usual after being gathered in the autumn."* And Dr. Bayley, in his account of the yellow fever in New- York in 1795, after describing the destructive effects of the "constitution of the air" upon cabba- ges, goes on to observe, that "the effects of a peculiar season were shown also upon different kinds of fruit. It was remarkable, that cherries * Medical Inq. and Obs. vol. iv. p. 45. 27 210 PHILOSOPHY did not come to that perfection in which we com- monly have them, and that they very soon showed a disposition to decay. Early in the season, the apple-trees were, very generally, extremely pro- ductive, and promised a large supply of their fruit in the autumn; but the expectations of the hus- bandman on this head were greatly disappointed ; the apples began to fall at least a month before the usual time, and in a very imperfect state ; and those which came to maturity could not be kept so long as it is common for them to be preserved." These facts conclusively show that epidemic meteoration is sometimes highly deleterious to vegetables. But it seems that some of the varieties of epi- demic meteoration which prevail in seasons of pes- tilence, are favourable to the growth and perfection of fruits. A striking variety of this kind existed during the plague in England in 1665. Dr. Hodges, in his account of that pestilence, states, " that this year was luxuriant in most fruits, espe- cially cherries and grapes, which were at so low a price that the common people surfeited with them," and that " the markets being open as usual, and a great plenty of all provisions, was a great help to support the sick; so that there was the reverse of a famine, which hath been observed to be so fatal to pestilential contagions ; and in this, the goodness of heaven is always to be remem- bered, in alleviating a common misery by such a profusion of good things from the stores of na- OF EPIDEMICS. 211 ture." The difference between the epidemic meteoration here noticed, and that previously adverted to, is very remarkable;! and we think it clearly evinces, that hitherto, sufficient atten- tion has not been given to the fact, that infec- tious epidemics are influenced by different kinds of epidemic meteoration—a truth highly important in a practical point of view. Upon the same principles may be explained the fact that epidemics are frequently concomitant with an extraordinary multiplication of insects. Heat, and in most instances, moisture, are essentially ne- cessary to their generation; but these alone seem inadequate to account for that prodigious increase of their numbers, which is observed in particular years. Certain states of the air, to us insensible, appear to be also necessary for their extensive *Loimologia, p. 20, 21. t At the first view, one might be inclined to ascribe these oppo- site phenomena to a difference in the sensible meteoration of differ- ent years. But the inquiries of Mr. Webster distinctly show, that such phenomena occur in seasons unlike each other, with re- spect to the manifest qualities of the air. " When excessive rains or dry seasons precede the failure of crops," says he, " men are at no loss to assign the cause ; although in these cases they may mistake the true cause. But it often happens, that grain fails of its usual perfection in seasons apparently the most temperate and favourable. Observing farmers remark, that, in certain years, when blast or mildew is expected from intemperate weather, a-rain proves to be good ; at other times, the grain will shrink very much under a series of weather apparently the most propitious." History of Pestilential Diseases, vol. ii. p. 99. 212 PHILOSOPHY fecundity; and it has long been observed, that those states of the atmosphere are generally favour- able to the prevalence of koino miasmal diseases. Pestilence, a strong tendency in dead animal and vegetable substances to rapid decomposition, a morbid condition and general deficiency or imma- turity of fruits, together with a vast amount of insect life, are so frequently coexistent, that there can be no hesitation in assigning to them a common de- pendence upon epidemic meteoration. It is not, however, every kind of epidemic mete- oration that occurs in the warm months, which con- tributes to the increase of insects. For it is ob- servable, that when contagious and meteoratious epidemics prevail in the summer and autumn, the animals in question are seldom extraordinarily multiplied. It is, therefore, those varieties of meteoration that exist during infectious epidemics, which generally animate the fields and marshes with the insect tribes ; and even among these varieties, there are probably some which do not particularly favour their generation. It is also worthy of re- mark, that in those pestilential seasons in which epidemic meteoration is specially suited to bring the ova of insects to maturity, the attendant sensible meteoration or unusual humidity of the soil, may prevent their evolution, or prove destructive to them. To the above reflections we may add, that should meteoration stimulate vegetables into vigorous health and fruitful luxuriance, and at the same time, OF EPIDEMICS. 213 exert an influence promotive of the multiplication of insects, the depredations of the latter on the former will rarely diminish the quantity of food to an amount that will endanger a famine ; but should insects abound in seasons when meteoration occa- sions a sickly condition and limited yield of fruits, whole plantations may be desolated, and conse- quently, man and beast be exposed to the most calamitous privations. 3. In what manner are the diseases of the infe- rior animals connected with Epidemics ? In adverting to this interesting subject, we have to premise, that it will be impossible to treat it satisfactorily until the science of epizootic etiology is entirely remodelled; for in its present state, the general truths of epidemics cannot be brought into a comparative examination with the loose state- ments and unarranged facts relating to the causes of diseases among brutes. To enter on this task at present would be incompatible with the limited design of this work. We may remark, however, that the plan we have pursued in arranging the causes of human diseases, will probably furnish an outhne for a correct classification of the remote causes of epizootic disorders. That there are dis- eases among the lower animals which are contagious, infectious, and meteoratious, is, perhaps, sufficiently evident; but whether they admit of the same sub- divisions, and are governed by the same laws as human disorders, remains to be determined. The difficulties which must attend inquiries on this 214 PHILOSOPHY subject, are pecuhar. There are, probably, some causes which are operative on all the species of domestic animals, and others which are peculiar to individual species. To discriminate those causes, and to ascertain their natural affinities, with a view to their generalization, will demand much patient research. A few cursory remarks on the more general causes, will embrace all we have to offer on this subject. The murrains which occasionally prevail through extensive districts of country, obviously arise either directly from meteoration, or from causes which owe their existence to its influence. Writers on epidemics have been at much pains to connect these murrains with popular diseases; but hither- to they have failed to discover any determinate affinities between them. The dependence of certain epizooties, however, upon meteoration, evidently renders it proper to consider them in connexion with epidemics. The appearance of diseases among domestic animals has long been regarded as indicative of an epidemic state of the atmosphere ; but it seems, the question has never been investigated, whether those dis- eases more frequently appear with contagious, than with infectious or meteoratious epidemics. Sometimes a disease rages among the inferior animals without being accompanied by a corres- ponding disorder in the human family, and vice versa ; at other times, an epizooty and epidemic pre- vail simultaneously. A satisfactory exposition of OF EPIDEMICS. 215 these apparent anomahes cannot be given, unless we resort to the varieties of insensible meteoration. The opinion has been long received, that an epi- zooty portends an epidemic ; and there are many examples in the history of popular diseases which seem to render it plausible. Facts of this kind are noticed by Homer, and other ancient poets. Thus it is said, that " On mules and dogs the infection first began, And last the vengeful arrows fix'd in man."* " For all those plagues which earth and air had brooded, First on inferior creatures try'd their force, And last they seiz'd on man."t That epizooties have frequently preceded pesti- lential and other epidemics, is undoubtedly true; but it is equally certain, that their occurrence is sometimes reversed ;| and consequently, there is no more propriety in asserting that epizooties forerun epidemics, than that the latter are precur- sors of the former. Without attempting to explain the intimate etio- logical relations between the diseases of man and brutes, we may observe, that the varieties of epi- demic meteorations afford a general explanation of the phenomena in question. Thus, some of those varieties appear to be ahke favourable to the pre- * Pope's Iliad, Book i. t Dryden's OZdipus. + See Edinburgh Encyclopaedia.—Art. Epizooty, 216 PHILOSOPHY valence of epizootic and epidemic disorders; others are not so, but favour the rise of the former to the exclusion of the latter, or contrariwise. The variable succession of these distempers appears to be owing to the transitions of insensible meteora- tion. When a meteoratious epizooty is prevalent, unat- tended by an epidemic, it is obvious, that the mete- oration which produces that epizooty is not directly injurious to man, for, were it so, an epidemic would necessarily exist. Should both, however, occur at the same time, a different variety of epi- demic meteoration must prevail, noxious alike to man and the lower animals. Knowing, therefore, that the insensible meteoration, which produces an epizooty, will not certainly change into a variety deleterious to man, it is manifestly improper to state it as a general truth, that the appearance of disease among brutes portends an epidemic. Even whether such a succession is more frequent than otherwise, is a question yet undetermined. As the remarks just made relate exclusively to meteoratious diseases, we have now to observe, that during the existence of infectious epidemics, the inferior animals are variously affected by the pre- vailing morbid influences. Sometimes a great mortality takes place among particular species; and at such times, birds occasionally flee from the pestilential region; at other times, none of these phenomena are remarkable. The several species of infection do not vary enough in their qualities OF EPIDEMICS. 217 to account for these phenomena, and consequently, we are compelled to attribute them to the varieties of epidemic meteoration, and particularly as they are frequently observed to occur without the reach of the pestilential miasm, the influence of which is usually circumscribed within narrow limits. Some of those varieties, however, may render domestic and other animals highly susceptible of the morbid impressions of infection, or this being innocuous, the insensible meteoration may, of itself, be ade- quate to their destruction. A full discussion of the subject of epizooties, and their connexion with epidemics, would embrace a view of all their efficient causes, and also, an inquiry into the predisposing influence of famine, unwhole- some food, and the effects of sensible meteoration on brute creatures. And in concluding, we cannot but express the hope, that some one competent to the undertaking, will enter upon the investigation; bearing in mind, that some of the most important advances in medical science have resulted from studies directed to comparative physiology and pathology. SECTION VII. A SUMMARY REVIEW OF THE NATURE AND OPERATIONS OF EPIDEMIC METEO- RATION I--AND CONCLUSION. It was incidentally remarked in a former section, that there is no time in which it can be said, that acute diseases do not derive a part of their charac- ter from the secret influences of the atmosphere. Hitherto, it has been the custom to speak of the insensible qualities of the air, only when diseases assumed an extraordinary character. But we ap- prehend, that there is as much propriety in consi- dering their simple and benign forms, as resulting, in a measure, from the operation of insensible me- teoration, as there is in ascribing malignant and anomalous effects to that cause. This idea is cer- tainly more consonant with the general economy of nature, than the supposition, that, at certain times, the atmosphere has no insensible influence on the human system. The probability is, that hi seasons of general health, the latent influences of the com- mon atmosphere are not essentially different in their nature from those which produce or favour the prevalence of epidemic diseases. It is true, those PHILOSOPHY OF EPIDEMICS. 219 occult quahties of the air which exert a genial influ- ence on the system, cannot, correctly speaking, be called epidemic meteoration; but still, in order to obtain a clear and enlarged view of the various properties of the atmosphere, it is no less impor- tant to consider those states of it which are salu- brious and give a mild cast to disease, than it is to investigate those which are manifestly morbid and destructive to life. The atmosphere surrounding the earth has, in every part of it, a two-fold influence on animal bodies; namely, sensible and insensible. The im- pressions arising from the former are well known to be extremely various ; and, it is probable, that the effects of the latter are equally diversified. Although there is no evidence that the two kinds of changes, which take place in the qualities of the air, have any dependence upon each other, yet the character of the one may be illustrated by that of the other. The temperature and moisture which constitute sensible meteoration, seldom correspond in any two countries remote from each other. They are also very different in the same country in different years or series of years. Sometimes, they vary from their ordinary range throughout a continent and hemisphere for several successive years, fluctuating, however, at all times, in diurnal vicissitudes. Hence the atmosphere, taken in its whole extent? presents a great variety of sensible modifications. 220 PHILOSOPHY which in some parts may be favourable to health, and in others productive of disease. Now insensible or epidemic meteoration is supposed to be of the same mutable nature. In one country, it may be conducive to general health ; in another, may occasion a meteoratious epidemic; in a third, may promote the extension of contagious diseases, and in others, favour the prevalence of infectious epidemics. In this manner, the atmosphere may manifest by its effects a great number of secret modifications which are similar in no two countries, or else alike, or nearly so, in several and distant districts at the same time. In instituting this comparison, we are aware that the variations of the secret qualities of the atmos- phere do not admit of graduation like those of temperature and moisture. That they do not range through a uniform scale or series of changes, when- ever they pass from one variety into another, is more than probable. Our only object in that compa- rison is to show, that the insensible qualities of the air are subject to variations as numerous and exten- sive as sensible meteoration, though governed by different laws. If, indeed, there be properties in the atmosphere which to us are insensible, and which are positively variable, we may fairly infer the probability, that their changes have relatively an influence on man, as diversified as the impres- sions of temperature. In this view of the subject, we entirely avoid the gratuitous hypothesis that epidemic meteoration OF EPIDEMICS. 221 arises from foreign and deleterious principles, casually introduced and extensively diffused through the atmosphere. A more philosophical conclusion is, that epidemic, like sensible meteoration, consists of certain modifi- cations or proportional combinations of the compo- nent parts of the atmosphere. Thus, the vicissi- tudes of temperature, considered as occasional causes of disease, do not imply the existence of extraneous and poisonous substances in the air; but only the increase and diminution in the quantity of a principle, namely, caloric, the presence of which in the atmosphere in certain proportions is essential to the well being of man. So epidemic meteoration probably consists of varied proportions of certain elements which enter into the natural composition of the atmosphere, and which, in given quantities, are essential to life. Every thing, how- ever, relating to the nature of the morbid occult quahties of the air, is yet involved in obscurity. We know of but one element, whose agency can be suspected of being principally operative in origi- nating them, viz. electricity; but how far this and the other constituents of the atmosphere are concerned in their production, we leave for the investigation of the meteorologist. Whatever be the nature of epi- demic meteoration, the first object of the practical physician should be to ascertain its effects, and to determine its laws ;—all of which, we think, may be done without a knowledge of its essential constitu. tion. We know nothing of the nature of gravita- 222 PHILOSOPHY tion or of mind ; and yet their phenomena may be analyzed, and systematically arranged; and why may not the same be accomplished with the phe- nomena of epidemic meteoration ? But to conclude: we are strongly inclined to doubt, whether any light can be thrown on the origin of the variable and frequently anomalous character of epidemics, by the study of mete- orology as it is usually prosecuted. Facts, relating to the peculiarities of the seasons, and the sensible qualities of the air, have been faithfully recorded for a long course of time ; and yet, multitudinous as they have become, they furnish no data from which we are enabled to assign the precise causes of atmospheric epidemics, or the various diatheses of other popular diseases. Indeed, we think, the time has arrived in which it is proper to abandon the expectation of being able to discover the origin and nature of those disorders, by observing and recording the quantity of rain, and the diurnal changes in the weight, temperature, and moisture of the air. Nevertheless, in another view of the subject, these phenomena are worthy of particular attention. Some of them are directly productive of common febrile and phlegmasial diseases, or co- operate as exciting causes, with various other mor- bific agents ; others are concerned in generating miasmal poisons, while all of them, acting as cli- matorial influences, tend to induce functional derangements, and also to modify, in a degree, the character of epidemics. The sensible qualities of OF EPIDEMICS, 223 the atmosphere, however, never occasion epidemic diseases, nor give to them those remarkably diver- sified appearances which they exhibit in different years. These arise, for the most part, from those states of the air which our senses and the instru- ments of philosophy are unable to detect. It is, there- fore, only by the study of epidemics, and particularly by observing their rise, progress, and decline, and by comparing their aspects and tendencies, as they appear in different years, under the same and op- posite circumstances of the weather, in a word, by making the human body in a state of disease, the instrument of research, that it will be possible for the physician to acquire a knowledge of the changes which take place in the secret properties of the atmosphere. THE END. tf*i • 4 %■ » « 6 l£-0\ * ' m'IwhH I* 8 I i«i lynr/l fep 1 vmli 11 JMd Bad & m