With regard to the original cause, our author observes, “that the plague is bred or produced originally from vitiated human effluvia, is a matter which has by no means been established on proper authority.” Setting aside therefore inquiries of this kind, he thinks it sufficient to inquire whether the infection be not communicated from a sick to a sound person by immediate contact; whether it be not also communicated at some distance through the medium of the air; and whether substances of various kinds do not imbibe the infectious effluvia, and retain them for a considerable time. So far as these points admit of proof from the experience of times past, the question concerning pestilential contagion will admit of a solution, independent of all theoretic reasoning whatever.
2. On the subject of contagion people have been embarrassed by confounding the true plague with other malignant diseases. This has been done, not only by the ancients, but by some moderns; and our author quotes Dr. Pye, saying “that any epidemic sickness, which rages with more than ordinary violence, and which occasions extraordinary mortality amongst mankind, may be, and is, properly termed a pestilence, or the plague.” By not attending to the proper distinctions, in these cases, circumstances belonging to what are commonly termed malignant or pestilential fevers will often come to be very improperly applied to the true plague.
3. “It may be remarked, that those who contend in favour of contagion, from zeal for accumulating proofs, have collected a number of facts from historical records of very unequal authority, and often with little critical skill in discrimination. Of this error their antagonists availing themselves, have selected from the mass the instances most liable to doubt or objection, and have endeavoured, by their manner of arranging them, to place the whole in a ridiculous light; while more important instances are either evasively past over, misstated in the representation, or invalidated by general declamation on the little credit due to historians in matters of physic, or the prejudices prevalent in ancient times of ignorance, and on contradictions to be found in the arguments of those who support the system of contagion.”
To this the Doctor adds the great quantity of hypothetical reasoning which has been introduced into the controversy, and above all the unfair dealing of the parties in carrying on the dispute, which has reduced the matter from “a calm inquiry in pursuit of truth, to a wrangling contest for victory.” Lastly he insists, that, had it not been for the misrepresentations and sinister dealings of those who have written against contagion, “the question seems to have been properly resolved in the affirmative;” and he complains greatly of the conduct of the Montpelier physicians in this respect, insomuch that “their misstating of circumstances, and the partiality so evidently discoverable in their narrative of cases, will serve more effectually to remove doubts on the subject, than any arguments that could be used against their hypothesis.”
On the subject of contagion our author observes, that some difficulties still remain; but these, though proper subjects of future inquiry, “do not appear to be of force sufficient to invalidate facts already established. It is well known, that the same person who has been inoculated two or three times for the small-pox without effect, even in an epidemic season, has afterwards received the infection upon repeating the operation at a distance of time when the disease was hardly sporadic. The cause of this remains unknown; but ignorance of it was never produced as an argument against the reality of variolous contagion. . . . If, of one hundred persons exposed to the infection of the plague by a near aproach to the sick, ninety should fall sick, shall human inability to assign satisfactory reasons for the escape of the other ten be converted into a positive proof against the disease having been caught by contagion? If persons retired from all commerce with the infected and their attendants, breathing the same air with the rest of the inhabitants, and nourished by the same aliment, remain untouched during the ravage of the plague, as long as they continue secluded, but, upon unguarded communication, are taken ill like others; can any rational doubt be entertained about the cause of their former security? Or if through stealth, or neglect of requisite precautions, substances tainted by the sick should be conveyed into these secluded retreats, and persons living temperately as before, ignorant of what had happened, and consequently in the midst of imaginary security, happen to be seized with the distemper; can it with any show of reason be ascribed, not to contagion, but to terror, or to colluvies in the stomach and bowels, produced by intemperance and bad aliment? The instances here alluded to are not the creation of fancy, but strictly consonant to repeated experience in Turky; to say nothing at present of what has been observed at Marseilles and in various cities in Europe.”
“But a greater difficulty than that of all persons not being equally susceptible of the infection arises from the cessation of the plague, at a period when the supposed contagious effluvia, preserved in apparel, furniture, and other fomites, at the end of a pestilential season, must be allowed to exist, not only in a much greater quantity than can be supposed to be at once accidentally imported by commerce, but in a state also of universal dispersion over the city: the fact, however unaccountable, is unquestionably certain; the distemper seems to be extinguished by some cause or causes equally unknown as those which concurred to render it more or less epidemical in its advance and at its height. In Europe something may be ascribed to the means employed for the cleansing of houses and goods supposed liable to retain the latent seeds of infection; but, at Aleppo, where the distemper is left to take its natural course, and few or no means of purification are employed, it pursues nearly the same progress in different years: it declines and revives in certain seasons, and, at length, without the intervention of human aid, ceases entirely.”
On this we shall remark in general, that the failure of contagion in some cases to produce the usual effects may proceed from some constitution of the body, disposing it not to allow the cause to produce its usual effects at one time, though at another, the constitution may be so far changed as very readily to admit it. This opinion has been very generally received among medical people, who have, to this singularity of constitution given the name of idiosyncrasy. It is, however laughed at by Mr. McLean. “As the fact (says he) cannot be denied, that a great majority have escaped after contact with persons ill of diseases supposed to be contagious, attempts may perhaps be made to account for it by supposing a certain peculiarity of constitution, which exempts from, or disposes to, disease. Is it the many who escape that have this happy peculiarity of constitution; or the few who are seized that are so unfortunate as to possesses it? The former are evidently too numerous to admit such an hypothesis. The property must therefore, I conclude, be given to the latter. But a child here and there is exempted from small-pox, although exposed to its contagion. In order to preserve a consistency, this fact must be accounted for by the same or another peculiarity of constitution. Peculiarities of constitution, then, exempt from contagion in one case, and dispose to it in another; and thus a term, which in reality means nothing, may be made to account for any thing. For my own part I confess my inability to comprehend any other peculiarities of constitution, or idiosyncrasies of habit, than what are constituted by the different degrees of health and disease; the different states of the excitability.”
In the same manner that Mr. McLean argues with regard to disease, let us argue concerning bodily strength. Some men are able to lift a weight of 6 or 700 pounds, but a great majority cannot lift above 300. Whence proceeds the difference? Is it the few who lift the great weight that by nature have more strength, or is it the many who can lift only the smaller that by nature have less? This is precisely his argument, and there needs no other refutation than stating it in this manner. What he calls the states of excitability are as much idiosyncrasies at the time as any thing else. Mr. McLean will not deny that a person debilitated by certain causes is more liable to be seized with typhus fever than one who is not. What does this proceed from, but that the body of the one is prepared for the disease, is constitutionally disposed to receive it, or has an idiosyncrasy of habit disposing to it, which the other has not? It is true, that unless we point out the circumstances which constitute this idiosyncracy we do nothing; but Mr. McLean’s scheme, of resolving every thing into excitability, would forever prevent us from doing so. This is the great deficiency of the Brunonian system altogether; for, by attending only to the animal life of the body, he seems to have absolutely forgot that we had any thing in common with vegetables. The bones, for instance, or indeed any part of the body, cannot be formed by the power which governs it after it was formed. The growth of the human body is as strict vegetation as that of a tree; and therefore we find that after the excitability is entirely gone, after death has taken place for a considerable time, the body still retains its form, and would do so forever, did not other powers interfere with it. Human life therefore is a compound of the vegetable and animal life, the former being the basis of the latter; and it is the vegetable life which is much more commonly the subject of disease than the animal life. In vegetables we observe an idiosyncracy of habit, as well as among animals. Some, even of the same species, are much more vigorous than others, and, among some, diseases are much more common than others. In like manner among the human race some are strong, others weak; in some the blood is much more confident, and coagulates on exposure to the air much more firmly than in others. Excitability, or excitement, is common to all, and the degrees of it (though enumerated by Yates and McLean in a kind of thermometrical scale) must be merely imaginary, because excitability is not the object of our senses. The obvious properties of the body itself, independent of any excitement whatever, are principally to be considered in medicine. These constitute the peculiar constitution, or the idiosyncracy of habit, belonging to each individual. Yet, in defiance of every confederation of these obvious properties, which all have access to observe, the new system leads us only to consider an invisible and unknown being called excitability. Hence diseases peculiar to certain constitutions more than others are said to be occasioned only by certain degrees of excitability common to all, or perhaps to consist in these very degrees themselves. Thus a peculiar mode of practice has been introduced, in which almost the whole materia medica is rejected. We have already quoted Dr. Girtanner, saying that all diseases whatever may be cured, as well as produced, by only four articles; but in the following quotation he goes still farther. “The art of pharmacy and the science of prescription will become useless; a phial of alcohol or laudanum will supply the place of that enormous quantity of drugs which crowd the shops of apothecaries. The trade of the druggist——but hold; if I continue this prophetic language, I shall only expose myself to ridicule,” &c. Reveries of this kind certainly deserve the most severe reproof. People may no doubt amuse themselves with theories as well as any thing else, while these theories continue inoffensive; but when the belief of them leads to a rejection of what has been established by the experience of many ages, they begin to assume a consequence which they originally had not. We have already seen that a disbelief of the doctrine of contagion leads people into a practice accounted dangerous by many, and which cannot be proved to be safe. A total rejection of medicines, the efficacy of which have been attested by thousands, and which never can be proved to have no efficacy, must be attended with still worse consequences, as thus we should be deprived of the means of curing those diseases which our imprudence in rejecting the former doctrine might have brought on. But, to return to the subject of the plague.
The disappearance of the disease, while all the causes that we suppose capable of producing it remain in full force, is a demonstration that it depends on something entirely distinct from the human body, and from all those powers which perceptibly act upon it. It proves that this unknown power has only a temporary existence, coming to perfection at one season, and dying away in another; sometimes capable of being revived, and sometimes not. This corresponds entirely with what has been laid down concerning contagion itself, viz. that like other aerial vapours it is capable of decomposition, and remaining for an uncertain length of time in a dormant state; but that occasionally it may revive, and appear unexpectedly, as mofetes arise from lavas, or damps in mines. After a city has been thoroughly infected with a pestilential disorder, therefore, there can be no security against its re-appearance; it being impossible to know whether the contagion may not be still existing and capable of being revived by some unknown cause, though it has been dormant ever so long. In such cases it may with propriety be said to have arisen spontaneously, though, had it not been there at a former period, there could be no reason to think that it would have appeared at that time.
Dr. Russel next takes into consideration the plague at Marseilles in 1720, of which he says the accounts “are more full, and circumstances better authenticated, than most of the accounts of anterior plagues to be met with in books.” From the opposition to the doctrine of contagion at the time, he also supposes that the facts relative to its introduction would be severely scrutinized, and falsehoods detected: “but (says he) if, instead of such detection, the most material have been passed over in silence, and little more than hypothetical reasoning opposed to others, the main facts may be considered as established, if possible, more firmly than they were before.” These facts are stated as follows: “1. That the plague did not exist in France before the 25th of May, 1720. 2. That it was imported in goods from the Levant, by a ship which left the coast of Syria the beginning of February, and arrived at Marseilles the 25th of May. Two days after her arrival one of the sailors died; an officer of quarantine who had been put on board died on the 12th of June, and a cabin boy on the 23d. Some porters employed in opening the merchandise at the lazaretto also died about this time. Three others were taken ill in the beginning of July, with buboes in the groin and axilla. This alarmed the surgeon of the lazaretto; a consultation was held with two other surgeons on the 28th; the disease was unanimously declared to be the plague, and the three patients died next day: the surgeon of the lazaretto, with part of his family, and the priest who attended the sick, were also taken ill and died.”