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CHAP. IX. Of the Existence of animal Spirits, and of their Use to account for animal Motion, and the other animal Functions

Filaments into which they are divided. That, on the contrary, as far as Leeivenhoeck (the beft Obfcrver doubtlcfs) or others who have examin’d the Matter with great Accuracy,could perceive: they appear lolid, tranfparent, and with broken Reflexions, even when dry, like crack’d Glafs-fVtre, Horn, or any other folid Subftance, without any ap-. parent Cavity. Nor that by compreffing them by Ligatures, flopping the Influx, or by ftroaking and milching their Lengths, are any Appearances to be obferv’d like thofe in other Veflels, which we know do carry Fluids in them, more than muft neceffarily happen from compreffing the fmall Arteries that go along by them. It is true, that by flopping and tying the Trunks o f the greater Nerves, the Mufcle it felf will turn Paralytick and Motionlefs, but it will equally do fo upon intercepting the Motion or Influx o f the Blood, which concludes nothing but this, that thefe Nerves arc neceffary towards the Adion of the Mufcles, whether from their carrying a Fluid, or from their own Tonick Nature, their internal Configuration, or any other Manner they may ad, is not thereby determin’d. And if Probabilities could any way influence a Fad, they muft He on the other Side of the Queftion, fince that thin and foft Liquor, which feems only fit to keep them moift and lax, rather derogates from the Exiftence of

any fpirituous Fluid in them proper for the intended End» Nor, thirdly, will I urge againft it Dr. Glijfons Experiment of putting the Arm of a ftrong, brawny Porter into a large Tube full of Water, and fixing it clofe to hi« Shoulder, that the Water might not get out, but alcend into a fmall conical Tube, paifing out of the Side o f the larger one: whereby he found, that upon the Itrongeft Aition o f the Muicles, the Water fubfided and fell in the fmall Tube, and rofe again upon tHeir ccafing to aft \ from whence he concludes, that Mtifcalar Mo­ tion is not performed by the Inflation or Swelling o f the Mufcles, but that, on the contrary, when they are mov'd, they are contracted into a leifer Figure, and morecompaftSubftance, or are hardened: which would icarccly happen, if any Matter, how fubtil io ever, flow’d in the Nerves, and thereby was added to the Subftance of the Muicles: For iince the Impenetrability o f Matter is demonitrable, the leaft fuch an Addition could eifed, was, that tho’ the Fluid, by its Subtilty, would not fenfibly increafe the Bulk, yet furely it could not leifen it. I lay, I ihall not urge thefe obvious Objeftions againft this I)o£hine; becauie, tho' 1 think they cannot befolidly anfwer’d, yet they may be evaded; but ihall proceed to offer a few Confidcrations, which I think-equally diftrefs it, in

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§. III. SoulE have imagin'd the Nature o f this Fluid of animal Spirits, to have lome Rcfemblance with that o f Light, (the moil fubtil, a&ive and penetrating Fluid appa­ rent in this our Syftem) which would make them quickly penetrate, fly through, tear, break, and confumc their rare and tender Prifons, which would be of no more Ufe to them, to dctermin them to regular and uniform Motions, than Glafs Tubes are to Light. And were they like urinous or inflammable Spirits; yet neither would fuch (lender Priions contain them any Time, or convey them uniformly for regular Purpofes. And Idjlly, if they were like Water or aqueous Fluids, they could neither have A&ivity nor Subtilty fufficient to folve the Appearances, nor could they move with Velocity enough to anfwer the Purpofes o f Volition, Senfation, and voluntary or invo­ luntary Motions, under that more grois and fluggiih Form, and would even then ouzc thro* their containing Tubes.