AS the Destruction likewise of this _Nexus_ in so subtile a Fluid leaves the saline Parts capable of injuring even that OEconomy which gave it Existence, so may its Volatility favour its Escape in a great Measure by Transpiration, so as to affect also other Persons within its Reach; and These with all other Particles of like Nature, which, by an Over-Agitation, and fermentative Motion of the animal Fluids, are separated from the softer and lubricating Compositions with which they were naturally joined, and which by their Volatility transpire and float in the Air, we take to be the true _contagious Miasmata_, that convey, propagate, and continue a _Pestilence_, after the Cause first raising it ceases. NOR will this seem strange to any who are accustomed to reflect, how many Substances are changeable into a poisonous Nature, which before were not only inoffensive, but useful to the Purposes of Life. Some Minerals, whose saline Parts in their Production are naturally blended with good Quantities of Sulphur, are harmless, and good _Alterants_; but when by any Means those Principles are separated, the saline Parts become strong _Emeticks_ and _Catharticks_, even to the Degree of a Poison. Who does not know that _Antimony_ may be taken crude in large Quantities without any manifest Effect, but that the Chymist can take somewhat from it, that in few Grains shall operate beyond the Power of a strong Constitution to bear? THOSE Arrows of Death therefore that make such dreadful Slaughter in a _Contagion_, are the animal Salts of infected Persons, set loose from their natural Combinations, and subtilized into the highest Degree of Volatility, by the Agitation and fermentative Motion of a Fever. And the Buboes, Carbuncles, _&c._ in a _Pestilence_, are nothing else but Collections of Particles, or Coalescences, formed in such irregular Motions, and thrown out of the Course of Circulation by those necessary Laws whereby every Thing is rejected, that cannot be assimilated into homogeneous and like Properties: The Matter of which Excretions is likewise of so subtile and fermenting a Nature, that if introduced into the Fluids of another well Person, it excites there the same Motion and Disorder. THIS change of animal Substances into a Poison, is too common a Truth to want any Attestation to those who have been but indifferently conversant in Natural Enquiries. And it is greatly to our Purpose, that even those Creatures, which are generally deemed poisonous, do require certain Degrees of Heat, and animal Action, to exalt their Juices to so high a Degree of Volatility, as to put on the Properties of a Poison, and act as such upon other living Creatures; insomuch that it is not only a common Observation that these Animals lose their poisonous Nature when remov’d into Climes colder than what is natural to them, but that also they are not so venomous in their own Climates, at the cooler Seasons of the Year, as in the most sultry.