IT is a Matter indeed of much more Difficulty to determine, how Particles from a gross Origin, should be raised to so great Volatility and Fineness; but this is very certain, that when they are elaborated in the most perfect Manner, they exceed even the Light and Activity of the Sun-Beams; and the brighter and more active they are, the better do they perform their Offices in the OEconomy, as from their Efficiency is procured a State of Health and Vigour both in Body and Mind. IT is of no great Moment to enquire, what Quantity of Spirit is necessary for the Conservation and Support of an humane Body, so that we do but know they partake of the Source from whence they are generated, insomuch that they are more or less perfect, according to the greater or lesser Degree of Purity in their productive Juices. BUT I must here acknowledge my self diffident in that Opinion of the Spirits being prepared of a different Nature for particular Parts, for according to the Influences of the Mind, and the Contiguity, Rectitude, or Consent of the Vessels, they are by a voluntary Act determined the same into this or that Limb or Part: Which is manifest enough in the Prick of a Needle, or a venomous Bite, from the great Affluence of Spirits to that Part; I have therefore no Notion of a continued Emanation of Spirits, but that on such Occasions they are called, by the Sensation upon the affected Part, from the nervous Origin where they are elaborated. _SECONDLY_, It sometimes happens that the Spirits degenerate from their native Purity, as also at others that they prove abortive, in not arriving to their utmost Maturity, whereby they lie more open to foreign Impressions of Distemperature. BUT when the juices, or common Promptuary from whence the Spirits are generated, is not uniform, genuine, and perfect in kind, it is impossible that Spirits should be made from it in any tolerable Perfection; for one may as well pretend to wash a Brick, or draw clear Water from a foul Spring, as expect pure and natural Spirits from a corrupt and vitiated Chyle; although even when the Chyle is in right Order, there may various Errors happen in the Generation of Spirits, as from too great an Heat agitating the Blood in a preternatural Manner, or from an imperfect or unequal Separation of Particles, or from too much Cold causing an Intermixture of Crudities; and again, although the Spirits are duly elaborated, yet they may run into irregular Motions, and be the Occasion of many Disorders: But what is most to the Purpose, they may sometimes also receive a Taint from external Impressions.