“minute distinct _biasts_, which had their origin from within, and rose up in little pyramidal protuberances, sometimes as small as pins’ heads, at others as large as a silver penny; having the pestilential poison chiefly collected at their bases,” &c. That the plague was by the ancients reckoned a disease of a nature different from all others, appears from Galen, as quoted by Deusingius. “What is called the _pestilence_ is most properly remarked by Galen not to be a _genus_ of any known disease. For whatever diseases and symptoms are associated with the plague, truly and properly so called, the same are wont to be called _pestilential_ diseases; of which indeed there are an innumerable multitude, and these not always nor every where the same.”[61] [61] Non esse certi morbi genus, id quod _pestilens_ vocatur, rectissime notatum a Galeno est (3 Epid. comm. 3. t. 20.) quicunque enim morbi ac symptomata consociantur pesti veræ proprieque diclæ, ijdem _morbi pestilentes_ apellari consuevere, quorum equidem innumerabilis existit cohors, ac non semper et ubivis eadem. (_Deusing. de Peste_, _Sect._ iii.) In like manner Diemerbroeck, as quoted by Allen, gives his opinion, that “The plague is something different from a fever, and a fever is only a symptom of it, as I have _very often_ observed; and therefore some very ill define the plague by a fever, since a fever does not essentially belong to it.... A pestilential fever, the _companion of the plague_, is not occasioned by a pestilential venom, but by the mediation of putrefaction; that is, it is not produced because the humours are infected with the pestilent venom, but because the heart, being irritated, overwhelmed and much weakened by the pestilent venom, can neither duly digest and rarefy, nor govern and sufficiently discharge the infected humours; which for this reason putrefy and acquire a preternatural heat, and so excite a fever; which by reason of the foresaid secondary cause, is different and distinct from the plague, and a symptom of it. This is confirmed both by the maxims and authority of the ancients and moderns, as well as by practice, and evident examples.” Thus it appears, both by fair reasoning by induction from facts, and from the authority of the greatest physicians, that the plague is certainly a disease by itself, and entirely distinct from all others. Hence it follows, that, though we could investigate the causes of fever in their utmost extent, we might still be ignorant of the true plague. That nothing, however, may be omitted, let us now consider what physicians have advanced on this subject, and what progress they have made in ascertaining the sources from whence so many direful calamities are derived.