NOW it appears by the Experiments mentioned in the _Preface_, of giving the _Plague_ to _Dogs_ by putting the _Bile_, _Blood_ or _Urine_ from infected Persons, into their Veins, that the whole mass of the animal Fluids in this Disease is highly corrupted and putrefied. It is therefore easy to conceive how the _Effluvia_ or Fumes from Liquors so affected may taint the ambient Air. And this will more especially happen, when the Humours are in the greatest Fermentation, that is, at the Highth of the Fever: as it is observed that fermenting Liquors do at the latter end of their intestine Motion throw off a great Quantity of their most subtile and active Particles. And this Discharge will be chiefly made upon those Glands of the Body, in which the Secretions are the most copious, and the most easily increased: such are those of the Mouth and Skin. From these therefore the Air will be impregnated with _pestiferous Atoms_: which being taken into the Body of a sound Person will, in the Nature of a _Ferment_, put the Fluids there into the like Agitation and Disorder. THE Body, I suppose, receives them these two ways, by the _Breath_, and by the _Skin_; but chiefly by the former. I THINK it certain that _Respiration_ does always communicate to the Blood some Parts from the Air: Which is proved from this Observation, that the same Quantity of Air will not suffice long for breathing, though it be deprived of none of those Qualities, by which it is fitted to inflate the Lungs and agitate the Blood, the Uses commonly ascribed to it. And this is farther confirm'd by what the learned Dr. _Halley_ has inform'd me, that when he was several Fathom under Water in his _Diving Engine_, and breathing an Air much more condensed than the natural, he observed himself to breath more slowly than usual: Which makes it more than probable, that this conveying to the Blood some subtile Parts from the Air, is the chief Use of _Respiration_; since when a greater Quantity of _Air_ than usual was taken in at a time, and consequently more of these subtile Parts received at once by the Blood, a less frequent _Respiration_ sufficed. AS to the _Skin_, since there is a continual Discharge made thro' its innumerable _Pores_, of the matter of _insensible Perspiration_ and _Sweat_; it is very possible that the same Passages may admit subtile Corpuscles, which may penetrate into the inward Parts. Nay it is very plain that they do so, from what we observe upon the outward Application of _Ointments_ and warm _Bathings_: which have their Effects by their finest and most active Parts insinuating themselves into the Blood.