AND it cannot be thought strange, that most who took the Contagion should have a Fever, to those who consider the Nature of a nitrous Spirit, especially when degenerated, and that from the most slight Cause it will take Fire, and excite Heat; and the Fever accompanying this present Sickness was of the worst Kind, both on Account of its State and Periods, sometimes imitating a Quotidian, and at others a Tertian; sometimes seeming to retreat, and at others attacking again with redoubled Fury: There was never a total Cessation, but sometimes a Remission for an Hour or two, although every Exacerbation was worse than the former; but this I pass by here, having Occasion hereafter to enlarge further thereupon. AT length therefore, to discharge my Promise in giving a short Account of a Contagion, as of a Disease that is communicable that Way only, and killing most it seizes, it is to be taken Notice, that the Infection of the pestilential Poison is not only transferrable from one Subject to another, either by mediate or immediate Contact, and exciting the same Symptoms; but all the Conditions likewise of its Exertion, are as conspicuous as the Noon-day Sun; wherefore those Arguments to prove the pestilential Corruption not to arise from Contagion, are trifling and not worth Notice, as altogether disconsonant to Reason and Experience; as after I have enumerated the Conditions of a contagious Exertion, I doubt not but to make this Matter clear to every one. FOUR Things chiefly are necessary to a Contagion: _FIRST_, That there is an Efflux of the contagious _Seminium_. _SECONDLY_, That there is a convenient _Medium_ for the contagious Particles to move through, and be conveyed by. _THIRDLY_, A Fitness in the Subject to receive and cherish the contagious _Effluvia_. And, _FOURTHLY_, A due Stay of this _Seminium_; of all which distinctly. THE Quantity of Necessaries daily taken in for Refreshment does evidently demonstrate, that insensible Perspiration is much larger than all other Evacuations together: But where a Pestilence invades, a yet much greater Wast is made that Way than in a Time of Health, by the intestine Colluctation and Struggle of opposite Principles in the animal Fluids; this is confirmed by the Observation of _Sanctorius_, who tells us, that Persons taken with a pestilential Contagion, immediately become much lighter, the _Effluvia_ of their Bodies breaking through on all Sides with Rapidity; for such is the Energy of the pestilential Taint, that it immediately subtilizes more thick Substances, and gives them such a Sharpness, as to cut their Way like so many Needles, or Wedges, and very often carry along with them those natural Spirits which should be a Preservative to the whole Frame: Hence sometimes follow Swoonings and Faintings that are fatal, and Indications of that Wast of Spirits that hath been made by the pestilential Poison.