the Brain is branched out to every Part of the Body in Tubes attending the Arteries, and if the Spirits circulate not in them, they must perspire or be difcharged at the Ends, otherwise they would be stagnant, and would need no new Supplies. Such a Degree of Cold as condenfes the Steam in the outward Ends of the Nerves, or in the Muscles, takes away the Sense of Feeling, and almoft the Power of Motion. What Effects different forts of Steam, different Quantities, fecreted or discharged at different Seafons, &c. may have upon the Nerves deferve to be traced, and nicely confidered. That what I call Steam will be fecreted into thofe Tubes is plain, and that there never is any Subftance or Fluid found in them is certain, and it seems not neceffary that they should be fo large, to convey the Senfe of touch ing to the Brain: And they are more likely than the Arteries, or any other Tubes, to have Outlets to the Muscles to convey the Steam which extends and contracts them alternately. Steam affects our Bodies with that Senfation, which Heat produces in Proportion to the Quantity of Corpufcles of Fire, or volatile Salts in it; When they are in too great Proportion, they can divide the Parts, &c. VOL. X. Ꮐ When

When in a due Proportion, it makes our Bodies warm, and it may rife with great Force by Fermentation, when loaded with proper Fluids, without affecting our Bodies with any confiderable Degree of Heat.

CHA P. XI.

The Sides of the greater Tubes, as Guts, Arteries, Veins, &c. compofed of leffer Tubes, their Difpofitions, and Uses.

AS all the greater Tubes in the Body,

fuch as Arteries, Veins, Ducts, Glands, &c. must be compofed of still leffer in Proportion with the Mouths of the smallest in each inward, or into the Infide of the Tubes, till their Ends terminate at the capillary Glands outward, or into the Stomach, Guts, &c. inward; they must receive Juices ftill thinner and thinner out of the Blood, and fecrete them into it again, or discharge them outward or inward, and filling the fmaller Veffels in the Sides, muft contract and straighten, and discharging or emptying them, lengthen and widen the Tubes they compofe; iffuing the Juices into the smaller,

thicken

"Tis

thicken the Blood, and fecreting them into the greater Blood-veffels thin it, &c. And they must be directed by the fame Agents and Caufes: At what Times, and for what Ufes, deferves to be nicely obferved, and well confidered, as well in the Lungs, Liver, Milt, Kidneys, &c. as in the outward Parts of the Body; but more particularly in the Sides of the Stomach and Guts, because their Effects seem to be of greater Confequence here. easier to conceive than defcribe, how filling or emptying finall Tubes which com pofe the Sides of a larger Tube, ftraightens or widens it. If there be fo many fmall Tubes parallel and touching with their Sides, that they can be filled and extended into Circles, and emptied fo, that their Sides may meet when they are empty, the Circumference of the great Tube will be near half the Length of the Circumferences of all the leffer ones; when the leffer Tubes are full, the Circumference of the great Tube, through the Centres of the leffer ones, will be but about one third of the Circumferences of all the leffer Tubes, and almost half of each lef fer Tube, and of the Fluid in each of them, will be within that Circumference. If the leffer Tubes be fo wide or fo few, that

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that they cannot be extended into Circles when they are filled, but fill the great Tube, their Outfides will form half Arches, and their Infides Triangles, each with a Point at the Centre of the great Tube. If there be many Rows of the leffer Tubes, which compose the Sides of the greater, of dif ferent Sizes, or in different Pofitions, fome parallel to the great Tube, fome environing it, fome diagonal to them, &c. emptying or filling; the leffer will widen or ftraighten, lengthen or fhorten, open or fhut the great Tube in the Manner aforefaid, and those twined about will comprefs the reft after the fame Manner. If there be feveral Folds of Skin composed of hollow Tubes or Bladders, round the Infides of any Part of the Guts, &c. of fufficient Size or Capacity, 'tis plain, that when those Veffels or Glands in Tubes, or Branches of Tubes are full, they will meet, fill up the Gut, or, &c. ply into the Folds of one another, and form a Valve or Stop; and when the Juice is discharged, and the Blood repelled out of them, these Veffels, Glands, &c. will fall down by the Sides of the Guts, or, &c. in Form of thin empty Skins, and make an open Paffage. The Valves in the Blood-Veffels, which only open one

Way,

Way, and are kept fhut when the Force on the Outfide is ftrongeft, and are open'd when the Force on the Infide is strongest, need be of no other Figure than those of Caulids in a Pump, and need no filling or emptying of the fmall Veffels, but only to be bended forward and backward, fo as to open and shut them.

С НА Р. XII.

A Defcription of the Ducts, &c. for fecreting, and the Glands for collecting and difcharging Juices out of the Blood.

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Lands are a Congeries of fmall Veffels, contrived to collect and difcharge, the neceffary Quantities of the feveral Sorts of Juices, which jointly we call Blood out of the Veffels in which it circulates. The Blood in a healthy Perfon should be compofed of fuch a Mixture of Juices, that together they may not be too crafs to pafs the fmallest Bloodveffels, nor too thin to let the Steam pervade them without circulating them; and of a fufficient Proportion of Corpufcles of each Sort and Size, neceffary to be fecreted

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