During the prevalence of the plague in Grand Cairo, no sporadic disease of any kind makes its appearance. The same observation is made by Sauvage, in his account of the plague at Alais, in the province of Languedoc[33].
The small-pox, though a disease of less force than the plague, has often chased it from Constantinople, probably from its being in a declining state. But this exclusive prevalence of a single epidemic is not confined to the plague and small-pox. Dr. Sydenham's writings are full of proofs of the dominion of febrile diseases over each other. Hence, after treating upon a symptomatic pleurisy which sometimes accompanied a slow fever, in the year 1675, and which had probably been injudiciously treated by some of those physicians who prescribe for the name of a disease, he delivers the following aphorism: “Whoever, in the cure of fevers, hath not always in view the constitution of the year, inasmuch as it tends to produce some particular epidemic disease, and likewise to reduce all the cotemporary diseases to its own form and likeness, proceeds in an uncertain and fallacious way[34].” It appears further, from the writings of this excellent physician, that where the monarchy of a single disease was not immediately acknowledged, by a sudden retreat of all cotemporary diseases, they were forced to do homage to it, by wearing its livery. It would be easy to multiply proofs of this assertion, from the numerous histories of epidemics which are to be found in his works. I shall mention only one or two of them. A continual fever, accompanied by a dry skin, had prevailed for some time in the city of London. During the continuance of this fever, the regular small-pox made its appearance. It is peculiar to the small-pox, when of a distinct nature, to be attended by irregular sweats before the eruption of the pock. The continual fever now put on a new symptom. It was attended by sweats in its first stage, exactly like those which attended the eruptive fever of the small-pox[35]. This despotism of a powerful epidemic extended itself to the most trifling indispositions. It even blended itself, Dr. Sydenham tells us, with the commotions excited in the system by the suppression of the lochia, as well as with the common puerperile fever[36]. Dr. Morton has left testimonies behind him, in different parts of his works, which establish, in the most ample manner, the truth of Dr. Sydenham's observations. Dr. Huxham describes the small-pox as blending some of its symptoms with those of a slow fever, at Plymouth, in the year 1729[37]. Dr. Cleghorn mentions a constitution of the air at Minorca, so highly inflammatory, “that not only tertian fevers, but even a common hurt or bruise required more plentiful evacuations than ordinary[38].” Riverius informs us, in his history of a pestilential fever that prevailed in France, that “it united itself with phrenitis, angina, pleurisy, peripneumony, hepatitis, dysentery, and many other diseases[39].”
The bilious remitting fever which prevailed in Philadelphia, in 1780, chased away every other febrile disease; and the scarlatina anginosa which prevailed in our city, in 1783 and 1784, furnished a striking proof of the influence of epidemics over each other. In the account which I published of this disease, in the year 1789, there are the following remarks. “The intermitting fever which made its appearance in August was not lost during the month of September. It continued to prevail, but with several peculiar symptoms. In many persons it was accompanied by an eruption on the skin, and a swelling of the hands and feet. In some it was attended with sore throat, and pains behind the ears. Indeed such was the prevalence of the contagion which produced the scarlatina anginosa, that many hundred people complained of sore throats, without any other symptom of indisposition. The slightest exciting cause, and particularly cold, seldom failed of producing the disease[40].”
I shall mention only one more authority in favour of the influence of a single epidemic upon diseases. It is taken from Mr. Clark's essay on the epidemic disease of lying-in women, of the years 1787 and 1788. “There does not appear to be any thing in a parturient state which can prevent women from being affected by the general causes of disease at that time; and should they become ill, their complaints will probably partake of the nature of the reigning epidemic[41].” I have said that the fever sometimes put on the symptoms of dysentery, pleurisy, rheumatism, colic, palsy, and even of the locked jaw. That these were not original diseases, but symptomatic affections only of the reigning epidemic, will appear from other histories of bilious fevers. Dr. Balfour tells us, in his account of the intestinal remitting fever of Bengal[42], that it often appeared with symptoms of dysentery, rheumatism, and pleurisy. Dr. Cleghorn and Dr. Lind mention many cases of the bilious fever appearing in the form of a dysentery. Dr. Clark ascribes the dysentery, the diarrhœa, the colic, and even the palsy, to the same cause which produced the bilious fever in the East-Indies[43]; and Dr. Hunter, in his treatise upon the diseases of Jamaica, mentions the locked jaw as one of its occasional symptoms. Even the different grades of this fever, from the mildest intermittent to the most acute continual fever, have been distinctly traced by Lancissi to the same marsh exhalation[44].
However irrefragably these numerous facts and authorities establish the assertion of the prevalence of but one powerful epidemic at a time, the proposition will receive fresh support, from attending to the effects of two impressions of unequal force made upon the system at the same time: only one of them is felt; hence the gout is said to cure all other diseases. By its superior pain it destroys sensations of a less painful nature. The small-pox and measles have sometimes existed together in the body; but this has, I believe, seldom occurred, where one of them has not been the predominating disease[45]. In this respect, this combination of epidemics only conforms to the general law which has been mentioned.
I beg pardon for the length of this digression. I did not introduce it to expose the mistakes of those physicians, who found as many diseases in our city as the yellow fever had symptoms, but to vindicate myself from the charge of innovation, in having uniformly and unequivocally asserted, after the first week in September, that the yellow fever was the only febrile disease which prevailed in the city.
Science has much to deplore from the multiplication of diseases. It is as repugnant to truth in medicine, as polytheism is to truth in religion. The physician who considers every different affection of the different systems in the body, or every affection of different parts of the same system, as distinct diseases, when they arise from one cause, resembles the Indian or African savage, who considers water, dew, ice, frost, and snow, as distinct essences; while the physician who considers the morbid affections of every part of the body (however diversified they may be in their form or degrees) as derived from one cause, resembles the philosopher who considers dew, ice, frost, and snow, as different modifications of water, and as derived simply from the absence of heat.
Humanity has likewise much to deplore from this paganism in medicine. The sword will probably be sheathed for ever, as an instrument of death, before physicians will cease to add to the mortality of mankind, by prescribing for the names of diseases.
The facts I have delivered upon this subject will admit of a very important application to the cure, not only of the yellow fever, but of all other acute and dangerous epidemics. I shall hereafter assign a final cause for the law of epidemics which has been mentioned, which will discover a union of the goodness of the Supreme Being with one of the greatest calamities of human life.