But moreover, a second Advantage arising from Exercise, is, that it gives the Solid and Nervous Parts a grateful Sensation, which in some Cases is not contemptible; a gentle Agitation of the Spirits being able to remove some Pain situated in those Parts, which perhaps nothing else would remove so surely and so soon. To explain the manner of this by a trivial Observation (if any thing in Nature can be so) let us consider, how we can separate the _Cuticle_ from the true _Cutis_ without Pain; it can’t be done with an Instrument without extream Pain, it can’t be done by Vesicatories without some Pain; but it may be done with Chafing without any Pain at all, or rather with some Pleasure, till you leave off Rubbing, and the Air comes to act upon the naked Fibres. Now this can’t be attributed to the Heat of the Part only, for then hot Medicines apply’d to the Skin; would do it as easily but must be suppos’d to be owing to a certain Agitation of the Spirits in the Extremity of the Fibres, which affects ’em with so agreeable a Sensation, as to surmount even the Pain of a Separation of their Covering, the Scarf-Skin. Now it will be allow’d by all, that whatsoever Sensation there is in the Extremity of the Fibre, the same there is at the Origine of it in the Brain; so that a pleasant Sensation in the Extremity, must needs be the same in the common _Sensorium_; and therefore ’tis easie to account for the good Effects of Frictions of the Limbs in some sort of Fits, by giving a new and different Motion to the Spirits, and thereby disengaging ’em from their disorderly Motions. And then if acting thus upon the Extremity of the Fibres produces such an Effect in ’em, ’tis natural to imagine, that that Motion, or gentle Concussion, which much after the same manner, in some proportion acts upon the whole Body of the Nerves, must affect ’em with a Sensation proportionably agreeable, and may prove sufficient to dispose the Spirits to leave their Displosions, and irregular Motions, when they happen to be so discompos’d, and consequently remove the troublesome Watchings and painful Symptomes occasion’d by those Displosions, when other Means prove ineffectual. Thus we see how natural it is for those Hysterick Persons, who are vexed with obstinate Watchings, to fall into a true and refreshing Slumber, by the Motion of a Chariot, when Opiats will have no effect upon ’em, but rather encrease their Watchings: The Spirits being the most stubborn Part of the Animal Oeconomy, and not always to be compel’d, even by that potent Drug. The abstruse Nature of this Part of the Animal Oeconomy, will not permit us to come at a fair Explication of these Phænomena, any otherwise, than by what we at different times experience; for we must first understand, as the Author of the _Dispensary_ very well expresses it. _How the same Nerves are fashion’d to sustain_ _The greatest Pleasure, and the greatest Pain._ Dispens. _pag. 3._