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into that bowel, and is there mixed with the aliment, as foon almoft as it paffes the ftomach: adding alfo as a remark, how grievously this fame bile offends the ftomach itself, yet cherishes the veffel that lies next to it.

Secondly, We have now the aliment in the inteftines, converted into pulp, and, though lately confifting of perhaps ten different viands, reduced to nearly an uniform substance, and to a state fitted for yielding its effence, which is called chyle, but which is milk, or more nearly refembling milk than any other liquor with which it can be compared. For the ftraining off of this fluid from the digefted aliment in the course of its long progress through the body, myriads of capillary tubes, i. e. pipes as fmall as hairs, open their orifices into the cavity of every part of the inteftines. These tubes, which

are fo fine and flender as not to be visible unless when diftended with chyle, foon unite into larger branches. The pipes, formed by this union, terminate in glands, from which other pipes of a ftill larger diameter arifing, carry the chyle, from all parts, into a common refervoir or receptacle. This receptacle is a bag large enough to hold about two table spoon

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fulls; and from this veffel a duct or main pipe proce ds, climbing up the back part of the cheft, and then creeping along the gullet till it reach the neck. Here it meets the river. Here it discharges itfelf into a large vein, which foon conveys the chyle, now flowing along with the old blood, to the heart. This whole route can be exhibited to the eye. Nothing is left to be fupplied by imagination. or conjecture. Now, beside the fubferviency of this whole ftructure to a manifeft and neceffary purpose, we may remark two or three feparate particulars in it, which fhew, not only the contrivance, but the perfection of it. We may remark, firft, the length of the inteftines, which, in the human fubject, is fix times that of the body. Simply for a paffage, these voluminous bowels, this prolixity of gut, feems in no wife neceffary; but, in order to allow time and space for the fucceffive extraction of the chyle from the digested aliment, namely, that the chyle, which efcapes the lacteals of one part of the guts, may be taken up by thofe of fome other part, the length of the canal is of evident use and conduciveness. Secondly, we must also remark their peristaltic motion; which is made up of contractions, following one another

another like waves upon the furface of a fluid, and not unlike what we obferve in the body of an earthworm crawling along the ground; and which is effected by the joint action of longitudinal and of spiral, or rather perhaps of a great number of feparate femicircular fibres. This curious action pushes forward the groffer part of the aliment, at the fame time that the more fubtile parts, which we call chyle, are, by a series of gentle compreffions, fqueezed into the narrow orifices. of the lacteal veins. Thirdly, It was neceffary that these tubes, which we denominate lacteals, or their mouths at least, fhould be made as narrow as poffible, in order to deny admiffion into the blood to any particle, which is of size enough to make a lodgement afterwards in the fmall arteries, and thereby to obftruct the circulation: and it was alfo neceffary that this extreme tenuity fhould be compensated by multitude; for a large quantity of chyle (in ordinary conftitutions, not less, it has been computed, than two or three quarts in a day) is, by fome means or other, to be paffed through them. Accordingly, we find the number of the lacteals exceeding all powers of computation; and their pipes

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pipes fo fine and flender, as not to be visible, unless filled, to the naked eye; and their orifices, which open into the inteftines, fo fmall, as not to be difcernible even by the b. ft microscope. Fourthly, The main pipe which carries the chyle from the refervoir to the blood, viz. the thoracic duct, being fixed in an almost upright pofition, and wanting that advantage of propulfion, which the arteries poffefs, is furnished with a fucceffion of valves to check the afcending fluid, when once it has paffed them, from falling back. These valves look upward, fo as to leave the afcent free, but to prevent the return of the chyle, if, for want of fufficient force to push it on, its weight should at any time cause it to defcend. Fifthly, The chyle enters the blood in an odd place, but perhaps the most commodious place poffible, viz. at a large vein in the neck, so fituated with refpect to the circulation, as fpeedily to bring the mixture to the heart. And this feems to be a circumftance of great moment; for had the chyle entered the blood at an artery, or at a diftant vein, the fluid, compofed of the old and the new materials, must have performed a confiderable part of the circulation, before it received that churn

ing in the lungs, which is, probably, necessary for the intimate and perfect union of the old blood with the recent chyle. Who could

have dreamt of a communication between the cavity of the inteftines and the left great vein of the neck? Who could have suspected that this communication fhould be the medium through which all nourishment is derived to the body? Or this the place, where, by a side inlet, the important junction is formed between the blood and the material which feeds it?

We poftponed the confideration of digef tion, left it should interrupt us in tracing the course of the food to the blood; but, in treating of the alimentary system, so principal a part of the procefs cannot be omitted.

Of the gastric juice, the immediate agent, by which that change which food undergoes in our ftomachs is effected, we shall take our account, from the numerous, careful, and varied experiments, of the Abbé Spallanzani.

1. It is not a fimple diluent, but a real folvent. A quarter of an ounce of beef had fcarce touched the ftomach of a crow, when the folution began.

2. It has not the nature of faliva: it has not the nature of bile; but is diftinct from both.

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