It is very plain, that animal Bodies are capable of being altered into a Matter fit to breed this Disease: because this is the Case of every one who is sick of it, the Humours in him being corrupted into a Substance which will infect others. And it is not improbable, that the volatile Parts with which Animals abound, may in some ill States of Air in the sultry Heats of Africa be converted by Putrefaction into a Substance of the same kind: since in these colder Regions, we sometimes find them to contract a greater Degree of Acrimony than most other Substances will do by putrefying, and also more dangerous for Men to come within the reach of their Action; as in those pernicious, and even poysonous Juices, which are sometimes generated in corrupted Carcasses: Of which I have formerly given one very remarkable Instance[48], and, if it were necessary, many more might be produced, especially in hydropic Bodies, and in cancerous Tumors. Nay more, we find animal Putrefaction sometimes to produce in these Northern Climates very fatal Distempers, though they do not arise to the Malignity of the true Plague: For such Fevers are often bred, where a large Number of People are closely confined together; as in Goals, Sieges, and Camps.
And perhaps it may not be here amiss to remark, that the Egyptians of old were so sensible how much the Putridness of dead Animals contributed towards breeding the Plague, that they worshipped the Bird Ibis for the Service it did in devouring great Numbers of Serpents; which they observed did hurt by their Stench when dead, as well as by their Bite when alive[49].
But no kind of Putrefaction is ever hightened in these European Countries to a degree capable of producing the true Plague: and we learn from the Observation of the Arabian Physicians, that some Indisposition of the Air is necessary in the hottest Climates, either to cause so exalted a Corruption of the forementioned Substances, or at least to enforce upon Mens Bodies the Action of the Effluvia exhaled from those Substances, while they putrefy. Both which Effects may well be expected from the sensible ill Qualities of the Air before described, whenever they continue and exert their Force together any considerable time.
What I have here advanced of the first Original of the Plague, appears to me so reasonable, that I cannot enough wonder at Authors for quitting the Consideration of such manifest Causes for Hidden Qualities; such as Malignant Influences of the Heavens; Arsenical, Bituminous, or other Mineral Effluvia, with the like imaginary or uncertain Agents.
This however I do not say with design absolutely to exclude all Disorders in the Air, that are more latent than the intemperate Heat and Moisture before mentioned, from a Share in increasing and promoting the Infection of the Plague, where it is once bred: for I rather think this must sometimes be the Case; like to what is observed among us in relation to another infectious Distemper, namely, the Small-Pox, which is most commonly spread, and propagated by the same manifest Qualities of the Air as those here described: Notwithstanding which, this Distemper is sometimes known to rage with great Violence in the very opposite Constitution of Air, viz. in the Winter during dry and frosty Weather. But to breed a Distemper, and to give force to it when bred, are two different things. And though we should allow any such secret Change in the Air to assist in the first Production of the Disease; yet it may justly be censured in these Writers, that they should undertake to determine the Specific Nature of these secret Changes and Alterations, which we have no means at all of discovering: Since they do not shew themselves in any such sensible manner, as to come directly under our Examination; nor yet do their Effects, in producing the Plague, point out any thing of their Specific Nature.
All that we know, is this, that the Cause of the Plague, whatever it be, is of such a Nature, that when taken into the Body, it works such Changes in the Blood and Juices, as to produce this Disease, by suddenly giving some Parts of the Humours such corrosive Qualities, that they either excite inward Inflammations and Gangrenes, or push out Carbuncles and Bubo’s; the Matter of which, when suppurated, communicates the like Disease to others: But of the manner how this is done, I shall discourse in the following Chapter.