FIRST, It is not at all to be doubted, but that what Art, which is the Imatator of Nature, can do, may be done by the Efficiency of a more powerful Agent; and the most expert Chymists do shew a certain Corruption of Salt; nor would it be any great Labour to discover here the Method how it is done, were it not a Crime to expose the Secrets of Nature on trifling Occasions. But if my Authority is not sufficient to support an Assertion of this Weight, I trust no one will reject the Conviction that arises from Effects, and therefore I shall restrain the Proof hereof to as short a Compass as possible. As then it is established by the concurrent Authority of Antiquity, that as Fire, as it is an Element capable of Degeneration, and seemingly of Corruption, may increase a pestilential Malignity by Means of its great Subtilty, its prodigious Increase, and swift Propagation; Qualities too which a Pestilence very much partakes of. That which they conceited of Fire, seems to me to be applicable in a much more philosophical Sense to that Spirit we are speaking of, and which so nearly resembles it. I am indeed a Stranger to any Thing in the Universe that makes so swift a Progress as a Pestilence, and therefore the infectious _Miasmata_ are in the sacred Scriptures styled _Arrows that fly in the Dark_; and howsoever certain are their Strokes, and tho’ by Means of their Fineness they penetrate into the very Marrow, they yet shun by their Subtilty our Conceptions. AS to the spreading of a Contagion from one to another, and so on to Thousands, there is nothing can be possibly more swift in the Progress of Fire; and it exceeds even _Antimony_ in the Retention of its Properties, though that loses them not in a thousand Infusions: But the instantaneous Progress of this Enemy to Mankind is best illustrated by the Rapidity of Light, which is not greater. But more of this we pass by till we come professedly to speak of a Contagion. SECONDLY, the particular Nature of the pestilential _Miasmata_, may be known from their peculiar Influence upon the saline Particles in a humane Body; for nothing acts with more Efficacy and Energy upon a saline Body, than another partaking of the same Quality; and nothing is more plain than that this nitrous Spirit is of more Efficacy than the _Alkahest_ it self, as by it the fibrous Parts of the Blood are immediately corroded and dissolved; and therefore after dangerous Hemorrhages, very little Coagulation can be obtained in the extravasated Blood, unless by its being exposed to the Cold: but as often as that does happen, do not we immediately find a Fixation of the Fluids, and a certain Congelation of the Juices, which greatly retards their rapid Motions, and sometimes brings even a total Stagnation: It’s furthermore of considerable Importance to our present Argument, that Spasms, the constant Attendants of a Plague, have their Origin from an acrid vellicating Salt in the nervous Fluid.