As for the Fluids; One would think the Shape and Make of the Blood-Vessels were sufficient alone to lead us into an Opinion of the Necessity of Exercise; by reason they all terminate in a Cone, they must needs resist the Passage of the Blood incomparably more than they would have done if they had been Cylindrical; and tho’ all the Branches of the Capillary Arteries, would, if taken Collectively, make a greater Diameter than that of the great Artery, yet the Consistence of the Blood, and the extreme Fineness of those invisible Meanders, require the frequent Pressure and Assistance of the Muscles to encrease the Circulation, which accordingly we always find very much augmented by those Means; yet ’tis the Result of this swifter Current of the Blood, which should be most valuable to us, I mean the better Digestion and Mixture of the various Particles convey’d into the Blood. I believe it will be allowed on all hands, that the best way to bring an Animal Fluid to a greater degree of Perfection, is Digestion; and the Excellency of that Operation consists in the just Degree of Heat which causes it; or, to speak perhaps more properly, in the just Agitation or intestine Motion of the Particles which may be suppos’d to occasion that Heat. The Standard or Measure of this Heat or Agitation in the Animal Oeconomy, is to be taken from what we observe in a Man in perfect Health, and in the Prime of his Age; when his Blood flows with its due Velocity, when there is an uninterrupted Secretion of all that is disagreeable to it, and it is wrought up to its florid Consistence, and a just proportion between the Serous and Grumous parts. Now this we may successfully imitate by repeated Exercise, when the Blood happens to be impoverish’d and Languid, we may encrease the Velocity of the Circulation, and consequently the Heat following upon it, by which a great many crude Particles will be attenuated and ripen’d, either for Mixture or Secretion, and there will be an equal Distribution of the attenuated Particles to the several Emunctories of the whole Body, by reason of the Solids co-operating with the Fluids; whereas it is often quite otherwise, when an internal Medicine is given design’d for one Secretion only, which may promote that, and perhaps hinder another; as a Medicine which agrees with the Stomach, sometimes offends the Head; for the Nervous Parts being, as it were, Passive in the Case, the Secretions cannot be so equally performed as when the whole Body is exercis’d. I would not be here mis-understood, as if I suppos’d that this first Effect of Motion, this Digestion, would avail in many Cases, as where an ill Ferment is lodg’d in the Glands, or where the Morbifick Particles have been long a forming, and are strongly combin’d in the Blood, but this may take place where a greater degree of Agitation is absolutely necessary; as when the Blood is Effete and Languid, when the Chyle comes into it dispirited, and when even a proper Medicine proves offensive