tended the Part; and there are fuch like Tubes in the Sides of the Blood-veffels, which when the Force which drives the blood is abated in any Part, fill and contract the Veffels in that Part, and keep them at that Extent, and empty when `the Force is encreafed there, and fo feem as if they ftraightned or widened thofe Veffels by their own Power: fo of the Lungs, and feveral other Parts, which are all performed by the Powers of Steam and Air, as each prevail upon, or in each Part, but most visibly in the Heart. Secondly, where fome Parts are fo compofed of Tubes or bladders fixed to a Ligament, which, at the other End is fixed to a folid Part, that extending the bladders, fhortens them, and draws the folid Part by the Ligament fixed to it, which is called voluntary Motion. Branches from the Arteries fill the Inteftines, Mufcles, &c. and branches of the Nerves fill them, with Steam from within, and branches from the Veins, fill them by the Preffure of the Air from without. The Force of the Steam must act upon the Arteries and Nerves outward, and the Preffure of the Air upon the Veins inward. The Action and Strength of the Muscles is compounded of the expanfive

Force

Force and Strength of the Steam, which by the Arteries or Nerves, fill the Veffels which compose them within; and of the Compreffure of the Atmofphere, which compreffes and binds up the Outfides, and forces the blood and Juices inward, from the Veins and Glands, into the Veffels which compofe them. * The Steam fills the Muscles, and by extending the bladders contracts the Part, then empties that Steam into the diftending Muscles, or lets it go off, and fills the diftending Muscle with other Steam, and the Air preffes them to their first Figure when they are emptied. The Muscles are guarded by the Compreffure of the Atmosphere from extending too far, or burfting, which they would be liable to, if it were taken off, and doubtless there are Veffels or Coats compofed of small Veffels, which are filled with Juices by the Preffure of the Air, to refift and keep them from extending their bounds. The blood is not only of proper Consistence to be driven by the Steam, to convey Nourishment to each Part, to afford an infinite Number of various forts of Juices, for

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* Some Experiments about particular Eluvia from animal Bodies, feem to encourage this Hypothefis, and make it deserve a nicer Enquiry.

for the feveral Ufes for each Part, and that fine Steam, they call Spirits, for the Ufe of the Nerves, to discharge the fuperfluous Parts at the Lungs, Pores, by Urine, &c. but perhaps also an Atmosphere for the Steam to work with, to extend the Parts by Explofion, as Fire does with Water; in the large Parts with common Blood, in the leffer Parts, the feveral Degrees of Juices fecreted out of it. The Size, Number, or Thickness of the Muscles or Fibres, wherein it was fuppofed Strength for Motion confifted, is proportioned to the Strength of the Steam, and Juices neceffary to contract, or draw the Parts which they are to act upon, or to refift the Force of the Steam, within the Part from extending too far, &c. these Parts have no active Power nor Force in themselves, fo their Strength cannot be greater or lefs, by being either small or large, only where the Sides of a Tube, or Veffel, or Part is compofed of a great Number of fmaller Veffels, it is intended to contract forcibly. Every Tube in the Body which compofes the Sides of any. of the inward Veffels, that is, fuch as the Steam extends outward, is extended by the Fluids preffed into it by the outward Air, and by that means the Tubes which

compofe

compofe the Sides of the Heart, are continually kept full and extended by the Fluids fo preffed into them; thence the Heart by the vaft number of Tubes, arterial, venial, and mufcular in its thick Sides, has continually a contractive Force, and would always remain ftrongly contracted, or with its Apertures closed, and its Sides together, if the force of the Steam did not alternately open it, and as that Strength is spent, it contracts: The Power or Force of the Contraction by, the Preffure of the Air, is encreased by the Number of the Tubes or Veffels which compose the Sides of an inward Veffel, as well as its Cavity is more ftraightened by their Numbers being extended, by which means the feveral Juices, as Gall, pancreatick, &c. are preffed out. Qu. When the Refiftance is weak within, and the folid Parts be moved, as I imagine, by thefe Agents, and after these Manners, will not this alfo clear the Ufes of the feveral Parts, make Anatomy plain? Quit the Anatomists of feeking for folid Parts, to perform Motions which Fluids perform? for Muscles to open where the Part is only to contract? and to contract where they are only to open? and of that infuperable Difficulty, that the force given

F3

by

by Muscles to the Heart, Brain, or any other Part, fhall move all the other Parts Lateral or and itself? *

fide PfAs the Arteries are branched out fmalfages for the Agents ler and smaller from the Heart, and the neceflary. Steam drives the Blood outward, the force

of the blood iffued out of an Artery into a Muscle, or Part to be extended from within, cannot be greater in Proportion to the Wideness of the Artery, than the Force with which it iffues out at the Ends of the Arteries into the Veins at that Diftance. And as the Veins from many fmall branches are collected into one before they reach the Heart, the force of the blood iffued out of a Vein, to extend any Part or Muscle inward by the Preffure of the Air, cannot be greater, than the Stop

it

Among their imaginary Agents, there is one the most abfurd of all, that is, the Contraction of the Dura Mater, this is called by Hoffman the Occafion of all convulfive Diforders; how this can poffibly contract itfelf, I only appeal to any Body who has open'd the Head of a dead Perfon; for he must know its Adhefion to the Skull, even at the Top to be fo ftrong as hardly to let the Skull be feparated from it, and at the Bottom in the Inequality, to adhere fo clofe, as to require the greatest Difficulty to feparate it; but when an Hypothefis is to be fupported, I am forry to fay it, it feems as it very little Regard were had to the Truth and Firmnefs of its Foundation, which in Phyfick must often be of very fatal Confequence; and I fancy every Body will condemn Ludere cum Corio humano, as well as Ludere cum facris.