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the great work of digeftion ; and according to this account, the offices of. every part will be very eafily underftood. The circular tftfdg of mufcular fibres, placed round the orifice of the oefophagus, are defigned to prevent the upper orifice of the fiomach from being too much diftended, whe- ther by our carelefsly fwallowing too large morfels, or by the action of vomiting. The ufe of the mufcular circles,
- at the bottom of the fiomach, is as eafily feen : the aliments received into this part of the fiomach, were it not for thefe circular arrangements of fibres, would remain there, and have no tendency given them to go out of the fiomach ; but
. by this wonderful Aructure, the whole bottom of the fto- mach can at once be put into a fafe and eafy, though a pow-
- erful contraction, by means of which the aliments are na-
turally .fent toward the pylorus for their difcharge. Thefe circles give the fir ft principle of the periftaltic motion of the fiomach, which is much the fame with that of the in teftines, . .
When the aliments have been thrown off from thefe circles, they are not .immediately, however, difcharged into the
- pylorus, but are. thrown upon thofe bundles of fibres, or fmall rnufcles, which make what has been before called the reticular coat of the fiomach. That part of this coat which immediately receives them, is -that compofed of fegments of circles, the convex parts of which are all placed toward
. the bottom of the fiomach ; and as thefe afterwards form their
■ contractions, their middle naturally elevates, and throws off the aliment itill toward the pylorus, and this is done with the more force, as the action of thefe fibres is ftrengthened by the longitudinal ones j and, in fine, thofe longitudinal fibres, which are attached to the bands that furround the pylorus, when they act, contract, or pull the other parts of the fiomach toward their insertions j fo that every thing tends to help the throwing the food upon the pylorus. The reticular coat of the fiomach has alfo other great ad- vantages ; it is eafily capable of extenlion, and coniequently gives the ftomach a capacity of enlarging, fo as to hold a larger quantity of aliments than it otherwife could ; a'nd when they act, fo as to.be appioaching toward their .natural ftate again after fuch diftsntion, this action, which is no other than their contraction, neceffarily throws the aliments toward the pylorus: this contraction is always fucceeded by a fmall dilatation again, and that by another contracti- on, and thefe alternately fucceeding one another, fo long as any of the aliments continue in ithe ftomach, conftitute
. what authors call its periftaltic motion. Although this mo- tion is very flight, and only a kind of vermicular undulation,
■■ which is fcarce . fenfible, yet there have not been wanting very great men, who have thought it fufficient tor the great work of digeftion, Thefe authors fet afide the ufe of ajiy liquors, or juices of the fiomach, mixing themfelv.es with the aliments, and give the whole to this motion, which t-ney call a kind of trituration, which they fay breaks the ali- ments into fmall and fine parts, by rubbing them againft
■ one another, and that thefe fine broken particles make what is called chyle; but it is ■ fcarce confonant to reafon, that fo weak a caufe fhould be productive of fuch great effects.
"This motion is no ftronger than the periftaltic motion of .. the interlines, and that is never fuppofed to have any fuch effects on their contents, but only, to pufth them forward. The liquor prepared from the food is known alfo, to be grey at its pafiing out of the fiomach, and only to acquire its white colour in the duodenum ; and how is . this accountable for on the plan of trituration only ? And finally, if that were all that was required to digeftion, to what purpofe did na- ture, which does nothing in vain, ordain fuch an abundance of fluids to be prefent in all places, where the aliments were 2 deftincd to undergo any change ? To know the abundant quantity of thefe, we need only follow the courfe of the food from the time of its being taken into the mouth to that of its. being changed into chyle. All the time that the teeth are chewing the food, the parotid glands a'fford a prodigious quantity of faliva, which runs into the mouth, mixes with it, and pafTes with it into the fiomach $ befide thefe,. alfo, there are many other fources. of the faliva, which all difcharge it at the -fame time,_but the quantity from thefe alone is not eafily conceived*. A foldicr had, by a wound in the cheek, one of the parotids cut in two, and had the wound clofed within, but not without ; it was obferved,. that whenever he ufed bis jaws in chewing, this one wounded, gland alone difcharged a quantity of lymph enough to wet- feveral napkins.; what then muft be the quantity at every meal difcharged from both, and from all the other fources together? Though this is all carried down into the fiomach, yet there frefh juices are added to it. Wepfer difcovered multitudes of glands in the human fio- mach, the orifices of which were very fenfible ; and befide thefe, Mr, Ruyfch difcovered feveral other eminences, which, by their refemblance to thofe in the fecond ftomach of an ox, fecrn to be only cafes enclofmg duffers of minute glands, all deftincd, with the others, to pour out their contents on the mafc of aliments. All thefe fluids, however, only change the food into a thick greyifh liquor, which is too coaife to be received into the lacteals, and needs a farther elabo-
S TO
ration. This elaboration changes it into a white liquor, which we call chyle ; and this is only performed in the duo- denum, where there can be no trituration, but where there is a very remarkable afiemblage of different liquors to effect it: for befide the common ones, the liver and gall-bladder difcharge into this inteftme a great quantity of bile by the ductus choledocus ; and the pancreas fends thither alfo a great deal of its lympth. Brunderus has obferved alfo, in this inteftine, a valt number of gljnds, which, according to him, make a fort of fecond pancreas : thefe all furnilh, alfo, a great quantity of liquor's to the duodenum, where this great change is made in the matter of the aliment; and it is very natural to conclude from the- whole, that it is By means of thefe liquors that this change is effected; and if it appear, that the lair change of the greyiln liquor of the fio- mach into chyle be wrought by thefe fluids, why fhould it be doubted but that nature, which is alike in all its works, has ufed the fame means in the firft change, and by the li- quors, mixt with the aliment's in the ftomach, has wrought them into that grey liquor they are found there changed in- to ? Trituration does not at all feem the bufinefs of the fiomach, nature we fee has appointed another part, the mouth, for that office, and has furnifhed that with hard- bodies, ca- pable of tearing and grinding things to pieces. The moft natural opinion, on the whole, feems therefore, that the office of the mouth was thus to rend and tear in pieces the aliments before their paffage into the fiomach, that there the juices might act more ftiongly upon them ; in the fame manner as the chemift beats and breaks to pieces the fubftances, which he is going to throw into proper liquors, to extract their tincture. Mem. Acad. Par. 17 19.. The digeftive power of the ftomach of fome fowls is vaffly greater than' that in men, or any other animals. Cryftal bullets, fome hollow, and others folid, have been cramrried I down the throats of hens, and have been found afterwards I ftrangely eroded, and eaten by the'jitices there. Hollow I buliets of glafs have been alfo crammed down by the mem- bers of the Florentine Academy, and' have been found after- wards riot only eroded' on their furface, bmt filled witHin with a whitiih liquor like cream, which teemed to prey upon their fubftarice. It is probable hence', that the ft rong- di- geftion of thefe fowls may be in fome frieafure owing to- a powerful menftruum in their fiomach; 'Mais and cryital are two things wholly indiflbluble by any trienftruums we are acquainted with, and yet they are corrbded here. This menftruum in the fiomach of thefe animals, affiftfed by what' the gravel-ffones, whfch they fwallow, are able to do in the manner of teeth, may very well deftroy, and reduce iubftances of fuch derife texture, as we fcarce know how to -manage. The glafs drop's With long tails, called Prince Ru- pert's drops, having, been, in the fame manner forced down the throats of capons, were found entire in the' fiomach wrier many days, arid burft as ufual on breaking oft* the tail. Thefe loft fofnewhat of their weight by. remaining in the fiomach fome tirrie, but the' fame fort of drops, when lin- tempered by heating In." the fire, ( loft a great deal in a Very fhort time. One of them, with which Redi .rriade.his expe- riments, loft four grains 'of its weight in, four days-,- and giving it to another fowl, it, in fix: days time, loft-' nine grains more. This is an argument, not drily of the.' ^aft power of digeftion in the ftomach of thefe fowls, but of the great difference of hardnefs there is between the fame glafs when tempered, by being dropped hot into water, and when untempered again by fire.
Experiments were alfo made, ,by giving diamonds, topazes, leaden bullets, jafpers; arid porphyry, to'the'fame animals, and -others of like kinds. The diamond loft nothing of its weight;- the topaz alm'oft nothing, the lo'fs being fcarce difcernible with nice fcales ;' other ftohes fcarce loft any thine, but the leaden bullets Toft oorifiderab'ly. ' Hence it is eafy to conclude, that the friia'll gravel -ftones, Which they pick up to ferve for grinding the food in their fiomachs, do their office without parting with a'lmoft any thing frofri themfehfes : thefe little, ftones, though lefs beautiful, Vet approaching 1 in their nature to the gems. There is great 1 difference, how- ever, 'between thefe and pearls; for it was found that 'fbur pearls given to a pigeon loft one third of their weight"' in twenty four hours, and eight fmall pearls/given to another pigeon loft two thirds' of their weight in two days. Jltdi, Efperienz. Stomach of fifm. The ftomach of fijhss is very different' in the various kinds, in reflect of flze, thickhels, and ittf' Se- veral properties and qualities; but its lituation is generally longitudinal, and it is fingle in all the known fifties, ex- cept in the firomatcus of Rolideletius, in which it is faid to be double.
The fiomach in living nth is cold tq'tfce touch, but this is only a proof that it ' is 'lefs tiot than 'OUT own flefh. That there -is heat in it, is evident enough . from the digeftion which is fo powerful in it, the fiomachs of many fifh. di- gefting fubftances which ours could not at a!! effect ; fuch are the mills of Ihell'fifli. it is not eafy to fuppofe this could be performed without fome degree of he'at in the part, but at the fame time we are informed by this how fmaH a
degree
