It has been an axiom in medicine, time immemorial, that no two fevers of unequal force can exist long together in the same place. As this axiom seems to have been forgotten by many of the physicians of Philadelphia, and as the ignorance or neglect of it led to that contrariety of opinion and practice, which unhappily took place in the treatment of the disease, I hope I shall be excused by those physicians to whom this fact is as familiar as the most simple law of nature, if I fill a few pages with proofs of it, from practical writers. Thucydides long ago remarked, that the plague chased all other diseases from Athens, or obliged them to change their nature, by assuming some of its symptoms. Dr. Sydenham makes the same remark upon the plague in London, in 1665. Dr. Hodges, in his account of the same plague, says, that "at the rise of the plague all other distempers went into it, but that, at its declension, it degenerated into others, as inflammations, head-ach, quinsies, dysenteries, small-pox, measles, fevers, and hectics, wherein the plague yet predominated[32]." [32] Dr. Hodge's Account of the Plague in London, p. 26. 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]. [33] Sed hoc observatu dignum fuit, omnes alios morbos acutos, durante peste siluisse, et omnes morbos acutos e pestis genere suisse. Nosologia Methodica, vol. i. p. 416.