AGAIN, the Pestilence is said to be contagious; because some are come to that Height of Boldness, (being blind with too much Light) to propagate strange Conjectures to the contrary, as if the late Plague was begun and continued by a foreign Influence; but to remove this Controversie, it may be convenient to explain the Nature of a Contagion, and its supposed Conditions of Exertion; but before I enter upon this, it will be necessary to dispatch the other Members of this Definition.
IT is further added, that the Plague affects many Regions together at the same Time, in Order to distinguish it both from Endemick Diseases, that is, such as are appropriate to one Place only; and also from Sporadick Diseases, which although they rage amongst the Populace in this or that Country or Climate indifferently, according to the Influence of their procatarctick Causes, they are yet to be deemed particular, as
well as they are pernicious: But enough of these Matters.
AT length then it becomes necessary to change the Consideration, and enquire how it comes that the Plague hath its chief Origin from a Change or Corruption of the nitrous Spirits in the Air: This is the great Difficulty! This is our Task! It is therefore to be hoped that the Novelty of the Opinion will not occasion any one to receive it at first Sight amiss, until by due Examination he hath brought it to Trial; but in Order to erect this upon a sure Foundation, it is proper to premise some Considerations.
AND first of all, the central nitrous Spirit does every where transpire and exhale towards the Surface, to recruit the Consumptions of Nature, and for other Purposes hereafter to be mentioned. From this saline Origin straining through the Bowels of the Earth, it is by every one understood Vegetation is carried on; and that the Light and vital Warmth of the Sun is impregnated by it through the whole Region of Air; and the mutual Intercourses or Operations upon one another
between the Sun’s Rays, and these saline Exhalations, by a Kind of Magnetism between them, is too obvious in a Multitude of Instances to want any Comment.
I know in nothing indeed where there is a greater Intercourse and Sympathy; and a considerable Illustration of which may be made by the following Experiment. If any one in the Spring-time, when the Sun is approaching nearer to us, digs up a Piece of Earth, and after Infusion and Filtration, evaporates the Liquor, he will find at the Bottom of the Vessel a Sixth Part of Salt more than at any other Time of the Year, from the same Quantity of Earth managed after the same Manner; the nitrous Salt for many Reasons not arising in so great a Quantity for the Exigencies of Nature, at any other Times; whence I conceive it manifestly to prove, that there is such an Efflux of this Salt as before suggested, and a Kind of Sublimation of it into the Air, and that this saline Spirit hath a Sort of Sympathy with the superior Heat. But that we may not use more Arguments than are necessary to prove the Energy of this Principle, every one who is doubtful herein may observe,
that not only Plants are produced and nourished by its subtle and luxuriant Insinuation into their Fibres, but that also from the same aerial Spirit the Life of Animals, and even the humane Species is preserved. And I cannot see any Difficulty in the Opinion, that the best Temperature of the Blood and animal Juices, the Renewal of wasted Spirits, the Restauration of Strength, and the good and healthful Constitution of the Viscera, Members, and whole Body, is maintained by the Assistance of this nitro-aerial Spirit. Nor does any Thing appear more congruous to Reason, than that from the same Cause does the Racy Spirit of the Blood arise, as it is not derivable from any other; nor is it my single Opinion, that from the same Principle it derives its Colour; but as there are no Arguments even objected to this Doctrine, it is needless to imploy more Time in its Vindication.
BUT further, it may happen that this nitro-aerial Spirit may various Ways be changed in its Properties; that is, either with Regard to its proliffick Influences, (if it may be so expressed) or, which much
oftner happens, in its accidental and adventitious Impurities.