In order to pursue this Discourse with greater Exactness, it is necessary to ease our Memory from carrying the different Particulars of seven Pages, and not to oblige the Reader to take, on trust, what is writ so long before. It may, perhaps, be useful to Dr. _Mead_ to tell us[3], that he, lately, left the _Air in a putrid State_; but that is nothing to us, who are at this present time sensible that the Doctor has not been able to bring the least Speck of Putrefaction into it. However, not to balk him in his projected Means, whereby it communicates its noxious Quality; he desires us to observe, that _Putrefaction is a kind of Fermentation, and that all Bodies in a Ferment emit a volatile active Spirit, of Power to agitate, and put into intestine Motions, that is, to change the Nature of other Fluids, into which it insinuates it self_. Now we have observed it, we find every Article of this Observation to be false; for Putrefaction does not always precede Fermentation, nor that every body in a Ferment emits volatile Spirits, nor that volatile Spirits have a Power to agitate, or to put into intestine Motions all Liquors into which they insinuate themselves; and still far less, that being put into intestine Motions, is to change the Nature of the Fluid thus put in Motion. What Use the Doctor may have for this Roll of precarious Assertions, time may tell us: for he has now got the Master-Key of all Philosophy, even _Fermentation_, into his Hand. By Fermentation _Stones_, _Metals_, _Plants_, _Animals_, and (if it pleases him) the _Pestilence_, are generated, and cherished. This makes Diseases; this cures them; by this we live, by this we die. [Footnote 3: Page 11.] Neither does this Machine only answer all our Wants in performing the greater, but even the smaller feats, as we chance to employ it: for if we are asked, why _Glow-birds_ shine in the Night? or why _wet Hay_ takes Fire of it self, _&c._ one short Answer is sufficient to all these, that these great Works are done by _Fermentation_. A Poet in ancient times, pronounced those Nations happy, that had their rural Gods growing in their Gardens. But I esteem the Man far more happy, who has at hand so ready an Answer to every thing: who has got a Machine equally serviceable on every occasion, the _Philosopher’s Stone_, the _universal Medicine_, the making a Plague.