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the Pipe compreffed by the outward Air ; the Force of the Steam would drive part of the Fluid beyond the Valve at the Bend, and its force would cease, and it waste there, and the Compreffure upon the returned Part of the Pipe, would force Part of the Fluid through the Valve at the End of the Pipe, into the Part of the Pipe between the two first Valves, where it would find a fort of a Vacuum, or lefs Refistance, during the firft Part of the Second of Time, after the Steam had pasfed the Valves, and before it had Time to be iffued in fufficient Quantity to open the first Valve, and refift it: and that Vacuum would be fomewhat enlarged by the Cold in the returning fluid, which would condense the Steam it should find there, and at the End of the Second of Time, the Steam would push through the first Valve, and Part of the Fluid, and itself, through the next two Valves, and beyond the Bend, fo fucceffively. If the Steam were not fecreted out of the Pipe by Pores or fome other Way, as 'tis out of Animals by their Lungs, Pores, Ureters, &c. the Steam would encreafe the Fluid, fill the Pipe, and hinder the Circulation.

СНАР.

CHAP. VI.

ing the

Agents.

Concern- The Agents affigned, which circulate the Blood, fecrete the Juices, perfpire and refpire the Halitus, Sweat, &c. with the Reafons for affigning them, confirmed by Obfervations, Reflections and Deductions.

TH

HAT the Blood in Animals circulates, and along with it, what enters into it, through the lacteal Veffels, till Part thereof be refpired, perfpired, fecreted by Urine, and Part be converted into Blood, Flesh, Bones, &c. is now taken for granted. That it requires a very great Force to circulate it, is demonftrable. That feveral, who have attempted to fhew what circulates it, have afcribed Powers or Faculties to Parts of our Bodies which they have not, and Actions which they are not capable of performing, few People doubt. our Growth, Life, and Action depend upon that Circulation, or upon fomething fecreted out of the Blood by that Circulation, and that most of our Disorders are occafioned by, and attended with unequal,

That

and

3

and disorderly Circulation, is very certain. That till the Caufe of this Circulation be of Difor known, 'tis likely the Remedies will be ders. uncertain; and though I profefs no Knowledge in Phyfick or Anatomy, I have employed fome Thoughts about natural and mechanical Operations, and the allowed Apology (for the Good of Mankind) will excufe me for offering my Thoughts upon this nice Subject, tho' they be not altogether right.

the Blood;

it.

That which is called the Circulation of Of the Cir the Blood, I take to be two contrary Mo-culation of tions, one going from the Heart along the and the Arteries to the extreme Parts of the Lungs, Caufes of Externals, and Inteftines, and the other" returning through the Veins to the Heart. Which two Motions, I think, are performed by two different Agents, the one within the Body, and the other without the Body.

figned,

Blood from

The first, I think, is performed by the The firft Steam raised out of the Meat, Drink, and Agent af Juices in the Stomach and Guts; which, which as it rarifies and expands, iffues by the drives the joint force of the Preffure of the Atmo- the Heart fphere, and its own Expanfion, from thethro' all Stomach and all Parts of the Guts, thro'the Body. the lacteal Veffels into the Receptaculum Chyli, and thence through the Chyle Duct VOL. X. D

into

The fe

gentwhich

returns it

into the * upper Part of the Vena Cava, and fo forward through the right Ventricle of the Heart, thence into the Lungs, where the Superfluity of it is dif charged, thence through the left Ventricle of the Heart, thence into the great Artery, thence into the leffer Arteries, to the extreme Parts of the Body, and of the Parts which ferve for Secretion or Discharge, where the Remainder of the faid Steam condenfes or perfpires.

The fecond (I think) is performed by cond A- the Preffure of the Atmosphere, which forces the Blood up the fmaller Veins, to the into the into the upper and lower Parts of the Vena Heartfrom Cava, to the Place where they unite, at the right Auricle of the Heart, where the Steam iffued at the inofculation of the Chyle Duct, into the Subclavian Vein, which is at the upper Part of the Vena Cava near the Heart, takes it.

the whole

Body.

The Ufe

of the Heart.

The Heart, I think, uses not, nor has any great Force to push the Blood forward, but is placed for a Check or Stop: The right Auricle and Ventricle to the Steam and Blood, iffued from the Vena Cava, and the left to the Blood, and Remainder of the Steam iffued from the Veins

* Or thus, Into the fubclavian Vein, and fo to the right Auricle, hence thro' the right Ventricle, into the Lungs.

Veins in the Lungs. And its Valves are fo contrived; thofe, from the Veins to open inward; and thofe, into the Arteries, to open outward, and fhut the contrary Way: That as the Mixture of Steam and Blood preffes out of the Veins, it opens the Valves into each Ventricle, fills the Ventricles, extends them, opens the Valves into the Arteries, and pushes forward, whereby the Force of the Steam behind is fpent, fo that the Valves from the Veins fhut, and the Motion of the Blood in the Ventricles is continued forward, and the Heart emptied jointly by the Elafticity of the Steam, the Compref fion of the Atmosphere, and the Contraction of the Muscles of the Heart; and fo fucceffively make a fort of Space or Vacuum, in each Ventricle, at once for the Blood to flow from the Veins, and the Steam from the Guts, * And it seems, that the Strength of the Steam in its D 2

common

Thro' the Auricles, it opens the Valves into each Ventricle, fills and extends them, and pushes forward thro' the Valves of the great Artery, and thus the Blood is brought to the Heart; and it is emptied jointly by the Elafticity of the Steam, the Compreffion of the Atmosphere, and the Contraction of its own mufcular Fibres; and fo by a continual Evacuation of the Ventricles, a Sort of Vacuum or Space is found for the fucceeding Blood and Steam, ready to pour itself in at the right Auricle from the Vena Cava, the Refiftance before it being removed.

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