BECAUSE then there is such a vast Difference between a _Pestilence_ arising from assignable Causes in the Air, _&c._ and a _Pestilence_ from a _Contagion_, as to the preservative Means especially against them; and that what we are now in most Apprehension of, is of the latter Kind; it most concerns us to be well acquainted with the Manner of Infection, as far as we can reason about Agents so extreamly minute and subtle. How all other _Antecedents_ to a _Pestilence_ exert themselves in their Influences over the animal OEconomy, _Bellini_ has brought even to a Demonstration; but as to a _Contagion_, he says little; which therefore, as introductory to some following Remarks, we shall here insert. ‘As this Coagulation and Fusion may go on so far as to set at Liberty, and perspire through the Surface of the Body, or with the Breath in Respiration, many noxious Particles, which may be so subtil and active, as to enter the cutaneous Pores of other Persons, or mix with that Air which they draw in Respiration, and when got into the Body, be able to make the same Change in the Blood, both as to its Coagulation and Fusion; hence it comes that such a Fever proves _contagious_, which is an inseparable Requisite to a _pestilential_ Fever. ‘But this is not only thus brought about; but also the dissolved, and dispersed Particles may longer adhere to some inanimate Bodies than others, as to Woollen and Linen Cloaths, Papers, _&c._ and these Particles may, by the Steam of a living Body, or by the Means of any other Heat, be put into Motion, so as to breath out of those Lodgments, where they quietly resided, and obtain so much Liberty, and Action on all sides, as will carry them into the cutaneous Pores of any Persons within their Reach, and infect them; and on this Account a _Pestilence_ may be brought from very distant Countries, lying a long Time in such Manner concealed, and then suddenly breaking out; with many other Circumstances of like Nature. ‘BUT if these subtile and active Particles be of that Nature, that they can penetrate the Pores of other Animals, and occasion a like Coagulation of their Blood, not only Men, but Brutes also, will be seized with a _Pestilence_; but this does not always very necessarily happen; because the Blood of Animals is different from humane Blood, so that although these Particles are supposed to get into it, it does not therefore necessarily follow that they must vitiate it, any more than will _Aqua Regia_ dissolve all kinds of Metals; but yet Brutes of all kinds, or some of them only, will be seized equally with Men, when this subtile and active Ferment, which penetrates the Surface, is of that Nature, as will taint the Blood of other Animals with those _pestilential_ Requisites.