In this, which our author seems to have designed as his grand argument, it is plain that the deficiency is as great as in any of the rest. If we suppose the plague, or any other epidemic disease, to arise from some general cause, let that cause be contagion or any thing else, it ought to operate upon all who come within its sphere of action, as Dr. Mosely observes of infection. If experience shows that it does not, the argument will hold equally against a constitution of the atmosphere, putrid effluvia, heat, cold, or any thing else; and in fact the Doctor fairly gives up the point at last, by resolving the whole into an unrevealed mystery. With regard to what he says about the plague at Marseilles getting into the convents, of which he presents us with such a catalogue, it is impossible to know what precautions were used, and we are assured that in Turky it is thought necessary for the Europeans not only to guard against a communication with their own species, but some of the brute creation also. Cats particularly are dreaded so much, that a general massacre of them commences among those who use precautions, the favourites of that species must be sent to a distance, and M. Volney mentions two merchants who had shut up their houses, and yet had the plague imported by a cat. In short, considering that infection is supposed to be altogether invisible and imperceptible, it is impossible to say how it may be conveyed, or to what extent it may occasionally act when once brought into a country. Dr. Fordyce is of opinion that the distance at which infection may act depends on the disposition of the air at the time; and he observes, that a difference in this respect is observable in the odoriferous effluvia of vegetables. “If the air be loaded with moisture, they reach to a much greater distance. Vapour arising from a field of beans, for instance, or a putrid ditch, is sensible to the nostrils at a greater distance if the air is moist.” He observes indeed that this has never been verified with regard to infection; but as it is evidently the case with putrid effluvia, which very often accompany infection, we may reasonably conclude that it is the case with the latter also.
Let us next take a view of what is advanced by the authors of The Science of Life upon this subject. Mr. McLean, who puts his name to this part, informs us of his conviction “that no general disease, which affects a person more than once during life, can ever be communicated by contagion;” and he defines contagion “a specific matter, generated in a person affected with disease, and capable of communicating that particular disease, with or without contact, to another.” It would here be no improper question, by what means he comes to know that a contagious disease can affect a person only once. But even this question is unnecessary. Dr. Guthrie gives an account of a gentleman who had the courage to inoculate himself for the plague, in consequence of which he had the disease with the concomitant symptoms of buboes, &c. Here then we see the plague communicated by “a specific matter generated in a person affected” with the same disease, i. e. by contagion, according to Mr. McLean’s own definition. The dispute therefore might stop, as this fact seems to be decisive on the subject; but as he has at great length insisted upon the argument last quoted from Dr. Mosely, it seems necessary to follow him a little farther.
“If a person (says our author) be affected with any disease, it will necessarily be communicated to every other person who comes within the infectious distance, and is not at the same time labouring under some disease higher in degree.” This proceeds upon a supposition that his theory is absolutely perfect and infallible; which, however plain it may appear to himself, will not probably be admitted by others without some proof. Indeed he himself afterwards adduces some facts which decisively overthrow it. “A child (says he) here and there is exempted from small-pox, even though exposed to its contagion.” How comes this to pass? The disease, we are told, is contagious, the child is exposed to the contagion, and yet is not affected. In all such cases it would be ridiculous to suppose the subjects labouring under a disease higher in degree than the contagion could produce. In numbers of instances of this kind the children were evidently in good health, and yet would perhaps be seized at an after period when no more exposed to contagion than they had been at first.
“Small-pox, measles, and other general diseases, which occur only once during life, never disappear, until the whole of those who have been within the infectious distance, and were not at the time labouring under some disease higher in degree, have received the infection. As these diseases are very mild, children sometimes resist the power of contagion from the superior force of some other diseases, although they may be so slight as to escape common observation.”
In this paragraph we have the favourite maxim of our author repeated, twice indeed, without a single fact to support it. Instead of this we find hypothesis heaped upon hypothesis, as the giants are said to have heaped mountains upon one another in order to get up to heaven. He first supposes that the infection of the small-pox seizes on the whole of those on whom it falls. The exceptions to this maxim he explains by another supposition, viz. that the contagion of the small-pox is counteracted by another disease. The second hypothesis is supported by a third, and that a very extraordinary one, that the small-pox (a disease which has destroyed innumerable multitudes) is very mild; and this third by a fourth, that the diseases which counteracted the contagion were so slight as to escape common observation. It was incumbent on Mr. McLean to have pointed out some of those diseases, and to have informed us how they came to counteract this contagion. But it is needless to argue with one who writes so extravagantly. Far from the mode of reasoning followed by Dr. Fordyce, who decided from the majority of facts, our author determines every thing by his own preconceived opinions. “That the power which occasioned disease at the Oxford assizes (says he) was not contagious matter, is proved by its producing diarrhœa in some, while it produced fevers in others.” But, if it was not contagious matter, what kind of matter was it? Or how comes our author to know that those who were affected by the diarrhœa were not likewise affected by fever? How many fevers are attended by diarrhœa, or how many cease when diarrhœa comes on! It would have been equally conclusive to say that the matter was not contagious, because some died and some recovered.
I shall only take notice of one assertion more, it being both tedious and unnecessary to follow him through the whole. “From every record of epidemic and pestilential diseases, it would appear, that they have their stated periods of recurrence; that these periods are such months as are most remarkable for vicissitudes of the atmosphere; that they become general only in those years in which these vicissitudes are extreme; that they do not occur in seasons when the heats or colds, however intense, are equable; nor in years when the state of the atmosphere is tempered throughout; and that they uniformly cease with the establishment of an equable state of the atmosphere, whether the weather be cold or hot. . . . In Aleppo, according to Dr. Russel, the Europeans regularly shut themselves up in their houses every year, at some period between April and July; and the rich natives begin to adopt the same plan, &c. . . . From this fact it appears, that the plague occurs at Aleppo, in a state more or less mild, almost annually, and that it commences and ceases at certain known periods. But it has been remarked that, in its most severe state, this disease recurs only at periods of ten years, or thereabouts: a regularity which cannot, upon any known principle, be attributed to a power of such casual application as contagious matter.”
In the beginning of this paragraph our author makes a bold appeal to every record of epidemic and pestilential disorders; but here we may ask, Has he consulted every record of these disorders? That he has not, we may readily believe; but even those which are hinted at seem either to have been very inaccurately consulted, or wilfully misrepresented. To evince this I subjoin the following abstract of what Dr. Alexander Russel says of the plague in general, with the annotations of his brother, Dr. Patrick, taken from Russel’s Natural History of Aleppo.
The inhabitants of Aleppo suppose that the plague visits them once in ten years, and that it is always imported; and the most severe plagues are thought by some to come from Damascus, while others contend that they come from the northward. Dr. Alexander Russel thinks this popular opinion of the return of the plague not altogether unfounded; and he thinks it also probable that it never invades Aleppo without having previously attacked either Damascus or Khillis, Aintab, Marash or Uufa. He thinks that its appearance always is in one of the maritime towns of Syria; if in Sidon, Byroot or Tripoli, Damascus is commonly the channel by which it reaches Aleppo; but, if it shows itself first at Scanderoon or Byass, its approach is by the way of Khillis or Aintab.
On this Dr. Patrick Russel observes, that the account of Aleppo being visited only once in ten or twelve years is confirmed by a letter from an English gentleman, in 1719, who had resided there for 30 years. The dates of the plagues which Dr. Patrick had procured were, 1719, 1729 and 1733. Another began in 1742, and terminated in 1744; from which time there was no return till 1757 or 1758, when it continued at Aleppo till 1762, and did not entirely quit the country till 1764. The plague of 1719 was said to come from the northward, but this appeared to want confirmation; but all accounts agree that it raged at Tripoli, Sidon, &c. two months before it appeared in Aleppo. Egypt was ravaged by the plague in 1728, as was also Byass and the neighbouring parts in the same summer; and next year it appeared at Aleppo. In 1732 it raged at Sidon, Tripoli and Damascus; next year it seized Aleppo.
Dr. Alexander goes on to inform us, that the disease never spreads much in winter. It advances with the spring, comes to its height in June, declines in July, and terminates in August. “None (he says) are ever seized with in September and October, not even in the plague of 1742, which returned three years successively;” but Dr. Patrick says that this was not confirmed by his experience in 1760, though he owns that the distemper declines remarkably at that period; and the natives are greatly inclined to have it believed that the distemper has totally ceased, and to deceive the Europeans in this respect. The times at which the Europeans shut up and come out of their confinement show only the increase or decrease of the disease, but not its beginning or ending. The plague of 1719 made terrible havoc. Europeans then shut up about the middle of March, and kept confined till the middle of July. In 1729 they did not shut up till the middle of May, and were not confined above a month, the number of sick being small. In 1733 they were confined from the middle of March to the middle of July, but the distemper was less violent than in 1719. In 1742 the time of confinement much as in 1729. In 1743 shut up April 11, and opened the middle of July. The plague violent, but less so than in 1733. In 1744 few shut up, the number of sick being inconsiderable. In 1760 they shut up on the 30th of June, and continued about a month. In 1761 shut up May 28, rode out Aug. 1, and opened completely the 10th of that month. In 1762 they were confined from the last week in May to the first of August. From 1762 to 1787, a larger period than usual, the city was free from the plague. In 1787 it broke out among the Jews in the month of April, increased in May, raged violently in June, and terminated in July.