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_.