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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 discharged at the Ends, otherwise they would be stagnant, and would need no new Supplies. Such a Degree of Cold as condenses the Steam in the outward Ends of the Nerves, or in the Muscles, takes away the Sense of Feeling, and almost the Power of Motion. What Effects different forts of Steam, different Quantities, secreted or discharged at different Seasons, &c. may have upon the Nerves deserve to be traced, and nicely considered. That what I call Steam will be secreted into those Tubes is plain, and that there never is any Suba stance or Fluid found in them is certain, and it seems not necessary that they should be fo large, to convey the Sense of touching 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 Sensation, which Heat produces in Proportion to the Quantity of Corpuscles of Fire, or volacile Salts in it; When they are in too great Proportion, they can divide the Parts, & Co ÑOL, X.
When in a due Proportion, it makes our Bodies warm, and it may rise with great Force by Fermentation, when loaded with proper Fluids, without affecting our Bodies with any considerable Degree of Heat.
C H A P. XI.
Arteries, Veins, &c. composed of lesser
A $ all the greater Tubes in the Body, A such as Arteries, Veins, Ducts, Glands, &c. must be composed of still lesser in Proportion with the Mouths of the smallest in each inward, or into the Inside of the Tubes, till their Ends terminate at the capillary Glands outward, or into the Stomach, Guts, &c. inward; they must receive Juiceş still thinner and thinner out of the Blood, and secrete them into it again, or discharge them outward or inward, and filling the smaller Vessels in the Sides, must contract and straighten, and discharging or emptying them, lengthen and widen the Tubes they compose ; issuing the Juices into the smaller,
thicken the Blood, and fecreting them in to the greater Blood-veffels thin it, &c. And they must be directed by the fame Agents and Causes : At what Times, and for what Uses, deferves to be nicely observed, and well considered, 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 Consequence here. 'Tis easier to conceive than describe, how filling or emptying finall Tubes which compose the sides of a larger Tube, straightens or widens it. If there be fo many smallTubes parallel and touching with their Sides, that they can be filled and extended into Circles, and emptied so, 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 lefler 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 lefser Tube; and of the Fluid in each of them, will be within that Circumference, If the lefser Tubes be to wide or fo few, G2 .
that they cannot be extended into Circles when they are filled, but fill the great Tube, their Outfides will form half Arches, and their Insides Triangles, each with a Point at the Centre of the great Tube. If there be many Rows of the lefser Tubes, which compose the sides of the greater, of different Sizes, or in different Positions, fome parallel to the great Tube, some environing it, some diagonal to them, &c. emptying or filling; the lesser will widen or straighten, lengthen or shorten, open or shut the great Tube in the Manner aforefaid, and those twined about will compress the rest after the same Manner. If there be several Folds of Skin composed of hollow Tubes or Bladders, round the Insides of any part of the Guts; &c. of sufficient Size or Capacity, 'tis plain, that when those Vessels or Ġlands 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 Vessels, Glands, &c. will fall down by the sides of the Guts, or, &c. in Form of thin empty Skins, and make an open Passage. The Valves in the Blood-Vessels, which only open one.
Way, and are kept îhut when the Force on the Outside is strongest, and are open'd when the Force on the Inside is strongest, need be of no 'other Figure than those of Caulids in a Pump, and need no filling or emptying of the small Vessels, but only to be bended forward and backward, so as to open and shut them.
CHA P. XII. A Description of the Duets, &c. for se
creting, and the Glands for collecting and discharging Juices out of the Blood.:
Lands are a Congeries of small VefU sels, contrived to collect and difcharge, the neceffary Quantities of the several sorts of Juices, which jointly we call Blood out of the Vessels in which it circulates. The Blood in a healthy Perfon should be composed of such a Mix= ture of Juices, that together they may not be too crass to pass the smallest Bloodvessels, nor too thin to let the Steam peryade them without circulating them; and of a sufficient Proportion of Corpuscles of each Sort and Size, necessary to be seG 3