is the very Soul of the Book, the subject Matter upon which every thing turns, the Cause of the Plague, and the Indication for preventing and curing the Plague, are to be drawn out of it. Besides, the most ancient and best Physicians knew nothing of Contagion, and far less of _Pestilential Contagion_; Words only brought in by Physicians in later times, and of Ignorance; and therefore such suspected Words ought to be well described and defined before they are made use of; either in discovering the Nature of abstruse Diseases, or when we are to found Methods of preventing or curing them, upon such Discoveries. To leave this Enquiry about Contagion to another Occasion, we will only observe, that this necessary Article is overseen and neglected by the Accurate Dr. _Mead_, for Reasons well known to himself, and easily to be guessed at by every body. It must be acknowledg’d that the Doctor’s way of writing and inquiring is very singular, the remaining part of his Book being carried on without Principles, or any known thing with which his Subject to be explained has any relation. But, as I have now undertaken to make this short Discourse more intelligible, I will pursue my Design in Dr. _Mead_’s Method, as far as that does not obscure the Subject: In that Case I will take the Liberty to keep the Thread of our Discourse as much in our view is it is possible. Dr. _Mead_ then having taken leave of _Contagion_, tells us, that this unknown _Contagion is propagated by three Causes, The Air, diseased Persons, and Goods transported from infected Places_. What a propagating Cause may be, shall be left to those that deal in Metaphysicks, to determine; it matters not what it appears to be, while the begetting Cause is unknown. As to Air, he now undertakes to shew us how it becomes _Infectious, and how it communicates its noxious Quality to other Bodies_. The first, by the Authority of _Hippocrates_ and _Galen_; but in this he mistakes his Authors, as he commonly does when they do not come up to his Purpose; for _Hippocrates_ is thought, by many Authors, not to treat of the Plague, in this third Book of his Epidemicks; _Galen_, in the Commentary quoted by Dr. _Mead_, is so far from thinking that _Hippocrates_ was resolved to give us Cases of the Plague, that he thought quite otherwise: And for the Truth of this Assertion, take an irrefragable Authority, _instar omnium_, the learned Dr. _Friend_, who says at the Remark [1]__Λοιμωδης_, hic non est proprie pestilens & contagiosus, siquidem in his morbis ab Hippocrate descriptis, nullum est contagii vestigium: Sed ut Galenus innuit aliud non est, quam _Επιδημια ὀλέθριος__. And a little after, _sed ipse titulus Galeno paululum suspectus est_. [Footnote 1: _Sect. 2._]