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This wonderful menstruum, the most active we are acquainted with in nature, is secreted by a distinct set of vessels that exist in the texture of the stomach, and empty themselves into its cavity by innumerable orifices invisible to the naked eye; and it is hence called gastric juice, from yaothp, which is Greek for stomach. : Mr. Cruickshank supposes about a pound of it to be poured forth every twenty-four hours. " The drink,” says he,“ taken into the stomach may be two pounds in twenty-four hours; the saliva swallowed may be one pound in the same period, the gastric juice another, the pancreatic juice another. The bile poured into the intestines Haller supposes about twenty ounces, besides the fluid secreted through the whole of the internal surfaces of the intestines ;'* which Haller calculates at not less than eight pounds in twenty-four hours,-a calculation, nevertheless, that Blumenbach regards as extravagant.

The quantity of the gastric juice, however, seems to vary very considerably, according to the demand of the system generally, or the state of the stomach itself. In carnivorous birds, whose stomachs are membranous alone, and, consequently, whose food is chymified by the sole action of the gastric juice, without any collateral assistance or previous mastication, this fluid is secreted in much larger abundance; as it is also in those who labour under that morbid state of the stomach which is called canine appetite; or when, on recovery from severs, or in consequence of long abstinence, the system is reduced to a state of great exhaustion, and a keen sense of hunger induces a desire to devour food voraciously and almost perpetually.

Such was the situation of Admiral Byron and his two friends, Captains Cheap and Hamilton, after they had been shipwrecked on the western coast of South America, and had been emaciated, as he tells us, to skin and bone, by having suffered with hunger and fatigue for some months. “The governor," says Admiral Byron, “ ordered a table to be spread for us with cold ham and fowls, which only we three sat down to, and in a short time des. patched more than ten men with common appetites would have done. It is amazing that our eating to that excess we had done from the time we first got among these kind Indians had not killed us; we were never satisfied, and used to take all opportunities, for some months after, of filling our pockets when we were not seen, that we might get up two or three times in the night to cram ourselves."I

When pure and in a healthy state, the gastric juice is a thin, transparent, and uninflammable fluid, of a weak saline taste, and destitute of smell. Generally speaking, it is neither acid nor alkaline ; but it appears to vary more or less in these properties, not only in animals whose organs of digestion are of a different structure, but even in the very same animal under different circumstances. It may, however, be laid down as an established rule, that in carnivorous and graminivorous animals possessing only a single stomach; this fluid is acid, and colours blue vegetable juices red; in omnivorous animals, as man, whose food is composed both of vegetable and animal diet, it is neutral; and in graminivorous ruminating animals with four stomachs, and particularly in the adults of these tribes, it has an alkaline tendency, and colours blue vegetable juices green.

There are two grand characteristics by which this fluid is pre-eminently distinguished; a most astonishing faculty of counteracting and even correct. ing putrefaction; and a faculty, equally astonishing, of dissolving the toughest and most rigid substances in nature.

or its ANTISEPTIC POWER abundant proofs may be adduced from every class of animals. Among mankind, and especially in civilized life, the food is usually eaten in a state of sweetness and freshness; but fashion, and the luxuri. ous desire of having it softened and mellowed to our hands, tempt us to keep several kinds as long as we can endure the smell. The wandering hordes of gypsies, however, and the inhabitants of various savage countries, and especially those about the mouth of the Orange river in Africa, carry this sort of luxury to a much higher pitch, for they have no objection to an offensive smell, and appear to value their food in proportion to its approach towards putrefaction. Now all these foods, whatever be the degree of their putridity, are equally restored to a state of sweetness by the action of this juice, a short time after they have been introduced into the stomach.

* Anat. of the Absorbing Vessels, p. 106.

† Physiol. Institut. xxvil. $ 410. | Voyage, p. 181. See also Hunter's Animal Economy, p. 196.

Dr. Fordyce made a variety of experiments in reference to this subject upon the dog, and found uniformly that the most putrid meat he could be made to swallow, was in a very short time deprived of its putrescency. We cannot, therefore, be surprised that crows, vultures, and hyenas, who find a pleasure in tainted flesh, should fatten upon so impure a diet; nor that the dunghill should have its courtiers among insects as well as the flowergarden.

The gastric juice has hence been employed as an antiseptic in a variety of cases out of the body.

Spallanzani has ascertained that the gastric juice of the crow and the dog will preserve veal and mutton perfectly sweet, and without consumption, thirty-seven days in winter; while the same meats immersed in water emit .a fetid smell as early as the seventh day, and by the thirtieth are resolved into a state of most offensive liquidity.

Physicians and surgeons have equally availed themselves of this corrective quality, and have occasionally employed the gastric juice, internally in cases of indigestion from a debilitated stomach, and externally as a check to gangrenes, and a stimulus to impotent and indolent ulcers. I do not know that this practice has hitherto taken place very largely in our own country, but it has been extensively resorted to on the Continent, and especially in Switzerland and Italy ; and in many cases with great success.

But the gastric juice is as remarkable for its solvent as for its antiputres. cent property. Of this any industrious observer may satisfy himself by attending to the process of digestion in many of our most common animals; but it has been most strikingly exemplified in the experiments of Reaumur and Spallanzani. Pieces of the toughest meats, and of the most solid bones, enclosed in small perforated tin cases to guard against all muscular action, have been repeatedly thrust into the stomach of a buzzard: the meats were uniformly found diminished to three-fourths of their bulk in the space of twentyfour hours, and reduced to slender threads; and the bones were wholly digested, either upon the first trial or a few repetitions of it. Dr. Stevens repeated the experiment on the human stomach by means of a perforated ivory ball, which he hired a person at Edinburgh alternately to swallow and disgorge, when a like effect was observed.

The gastric juice of the dog dissolves ivory itself and the enamel of the teeth ; that of the hen has dissolved an onyx and diminished a louis-d'or;* even among insects we find some tribes that fatten upon the fibrous parts of the roots of trees, and others upon metallic oxides. And it is not long since that, upon examining the stomach and intestinal tube of a man who died in one of the public hospitals of this metropolis, and who had some years before swallowed a number of clasp-knives out of hardihood, their handles were found digested, and their blades blunted, though he had not been able to discharge them from his body.

It is in consequence of this wonderful power that the stomach is sometimes found in the extraordinary condition of digesting itself; and of exhibiting, when examined on dissection, various erosions in different parts of it, and especially towards the upper half, into which the gastric juice is supposed to flow most freely. It is the opinion of Mr. John Hunter,t however, whose opinions are always entitled to respect, that such a fact can never take place except in cases of sudden death, when the stomach is in full health, and the gastric juice, now just poured forth, is surrounded by a dead organ. For he plausibly argues, that the moment the stomach begins to be diseased, it ceases to secrete this fluid, at least in a state of perfect activity; and that so long as it is itself alive, it is capable, by its living principle, of counteracting the effect of this solvent power. Yet a case has lately been published by Mr. Burns of Glasgow, in which the stomach appears to have been eroded, although the death, instead of being sudden, did not take place till after a long illness and great emaciation of the body. It is possible, however, that even here the stomach did not participate in the disease. That the living principle of the stomach is capable, so long as it continues in the stomach, of resisting the action of the gastric juice, can hardly he questioned. And it is to the superior power of this principle of life, that worms and the ova of insects are so often capable of existing in the stomach uninjured, and even of thriving in the midst of so destructible an agency.

• Swammerdam, Biblia Naturæ, p. 168.

| Phil. Trans. 1772.

But though the solvent juice of the stomach is the chief agent in the process of digestion, its muscular power contributes always something, and in many animals a considerable proportion, towards the general result; and hence, the shape and structure of this organ, instead of being uniformly alike, is varied with the most skilful attention to the nature of the mechanism by which it is to operate.

In its general construction the stomach of different animals may be divided into three kinds; membranous, muscular, and bony. The first is common to graminivorous quadrupeds, and to carnivorous animals of most kinds; to sheep, oxen, horses, dogs, and cats; eagles, falcons, snakes, frogs, newts, and the greater number of fishes, as well as to man himself. The second is common to graminivorous birds; and to granivorous animals of most kinds ; to fowls, ducks, turkeys, geese, and pigeons. The third, to a few apterous insects, a few soft-bodied worms, and a few zoophytes; to the cancer-genus, the cuttle-fish, the sea-hedgehog; tubipores and madrepores.

Of the membranous stomach we have already taken notice in describing that of man; and at the bony stomach we took a glance in a late lecture on the teeth and other masticatory organs. It only remains, therefore, that we make a few remarks on that singular variety of the membranous stomach which belongs to ruminant animals, and on the muscular stomach of granivorous and graminivorous birds.

All animals which ruminate must have more stomachs or ventricles than one; some have two, some three; and the sheep and ox not less than four. The food is carried down directly into the first, which lies upon the left side, and is the largest of all; the vulgar name for this is the paunch. There are no wrinkles on its internal surface; but the food is considerably macerated in it by the force of its muscular coat, and the digestive secretions which are poured into it. Yet, in consequence of the vegetable and unanalogous nature of the food, it requires a much farther comminution; and is hence forced up by the esophagus into the mouth, and a second time masticated; and this constitutes the act called rumination, or chewing the cud. After this process, it is sent down into the second ventricle, for the esophagus opens equally into both, and the animal has a power of directing it to which. soever it pleases. This ventricle is called the bonnet or king's-hood; its internal surface contains a number of cells, and resembles a honey-comb; it macerates the food still farther; which is then protruded into the third ventricle, that, on account of its very numerous folds or wrinkles, is called manyplies, and vulgarly many-plus. It is here still farther elaborated, and is then sent into the fourth ventricle, which, on account of its colour, is called the red, and by the French le caillé, or the curdle, since it is here that the milk sucked by calves first assumes a curdled appearance. It is thus that the process of digestion is completed, and it is this compartment that constitutes the true stomach, to which the others are only vestibules.

There are some animals, however, which do not ruminate, that have more than one stomach; thus the hampster has two, the kangaroo three, and the sloth not less than four.* Nor does the conformation terminate even with

• Wiederann, Archiv, b. i

quadrupeds ; for among birds the ostrich has two ventricles,* and among fishes the stomateus hiatola. The horse and ass, on the contrary, though graminivorous quadrupeds like the ox, have only one stomach.

There may seem, perhaps, something playful in this application of different systems of mechanism to the same class of animals, and of the same system to different classes : but it shows us, at least, that the hand of nature is not necessarily fettered by its own general laws, nor compelled, even under the same circumstances, to adopt the same cause to produce the same effect. Yet, if we had time, we might proceed beyond this remark, and point out, if I mistake not, the reasons for such diversities, and the skill with which they are introduced. Thus the horse and ass are formed for activity, and require lightness; and hence the bulk and complexity of three or four stomachs would counteract the object for which they are created; but it does not interfere with the pursuits of the ox, which is heavy and indolent in its nature; and which, though it may perhaps be employed as a beast of burden, can never be made use of for speed. The activity of the horse and ass, moreover, excites, from the stimulus it produces, a larger secretion of gastric juice than is met with in the ox, and thus in a considerable degree supplies a substitute for the three deficient stomachs; but it by no means extracts the nutriment so entirely from the food introduced into it; and we hence see the reason why the dung of horses is richer than that of black cattle, and why they require three or four times as much provender.

We may apply the whole of these remarks to the ostrich, whose peculiar habitation is the sandy and burning deserts of the torrid zone, where not a blade of grass is to be seen for hundreds of miles, and where the little food it lights upon must be made the most of. The double stomach it possesses enables it to accomplish this purpose, and to digest coarse grass, prickly shrubs, and scattered pieces of leather, with equal ease. This animal is supposed to be one of the most stupid in nature, and to have no discernment in the choice of its food; for it swallows stone, glass, iron, and whatever else comes in its way, along with its proper sustenance. But it is easy to redeem the ostrich from such a reproach, at least in the instance before us; for these very articles, by their hard and indestructible property, perform the office of teeth in the animal's stomach; they enable it to triturate its food most minutely, and to extract its last particle of nutriment. It is true that in the class of birds, or that to which the ostrich belongs, a double stomach must necessarily, to a certain extent, oppose the general levity by which this class is usually characterized. But the wings of the ostrich are not designed for flight : they assist him in that rapidity of running for which he is so celebrated, and in which he exceeds all other animals, but are not designed to lift him from the earth. In reality, the ostrich appears to be the connecting link between birds and quadrupeds, and especially ruminant quadrupeds. In its general portrait, as well as in the structure of its stomach, it has a near resemblance to the camel; in its voice, instead of a whistle, it has a grunt, like that of the hog; in its disposition, it is as easily tamed as the horse, and like him may be employed, and often has been, as a racer, though in speed it outstrips the swiftest race-horse in the world. Adanson asserts, indeed, that it will do so when made to carry double ; and that, when at the factory of Podore, he had two ostriches carefully broken in, the strongest of which, though young, would run swifter, with two negroes on his back, than a racer of the best breed.

Yet widely different is the mechanism of the stomach in birds of flight that feed on vegetables : nor could any contrivance be better adapted to unite the two characters of strength and levity. Instead of the bulky and complicated compartments of the membranous stomach of ruminant animals, we here meet with a thick, tough, muscular texture, small in size, but more powerful than the stoutest jaw-bone, and which is usually called GIZZARD.

It consists of four distinct muscles, a large hemispherical pair at the sides, and two smaller muscles at the two ends of the cavity. These muscles are

• Valionieri, Anatomia, &c. p. 159, 1713.

distinguished from the rest belonging to the animal, not less by their colour than by their prodigious strength; and the internal cuticle with which they are covered is peculiarly callous, and often becomes quite horny from pressure and friction.

The gizzard of grazing birds, as the goose and turkey, differs in some degree in the formation of its muscles from that of granivorous. They have also “a swell in the lower part of the esophagus, which answers the purpose of a reservoir, in which the grass is retained, macerated, and mixed with the secretions poured out by the glandular surfaces surrounding it, in this respect corresponding to the first and second stomachs of ruminating animals, in which the grass is prepared for mastification,"* though essentially lighter.

In most birds, indeed, we meet with an approach towards this, in a cavity situated above the muscular stomach, and called the crop, or craw. This first receives the food from the mouth, and slightly softens it by a mucous fluid secreted from its interior; and thus prepared, a part of it is given back to the young, where there are young to partake of it, and the rest is sent to the gizzard or proper stomach, whose muscular mechanism, in conjunction with its gastric juice, soon comminutes it into the most impalpable pulp. There are several kinds, however, that, like the ostrich, endeavour to assist the muscular action by swallowing pebbles or gravel ; some of which find this additional aid so indispensable, that they are not able to digest their food, and grow lean without it. Spallanzani attempted to prove that these stones are of no use, and are only swallowed by accident; but their real advantage has been completely established by Mr. J. Hunter, who has correctly observed, that the larger the gizzards, the larger are the pebbles found in them. In the gizzard of a turkey he counted two hundred; in that of a goose, a thousand.

Reaumur and Spallanzani have put the prodigious power of this muscular stomach to the test, by compelling geese and other birds to swallow needles, lancets, and other hard and pointed substances; which, in every experiment, were found, a few hours afterward, on killing and examining the animal, or on its regorging them, to be broken off and blunted, without any injury to stomach whatever.

Yet, as all animals are not designed for all kinds of food, neither the force of the strongest muscular fibres, nor the solvent power of the most active gastric juice, will avail in every instance. The wild-boar and the vulture devour the rattlesnake uninjured, and fatten upon it; but there are many kinds of vegetables which neither of these are capable of digesting. The owl digests flesh and bone, but cannot be made to digest grain or bread; and in one instance died, under the experiments of Spallanzani, when confined to vegetable food. The falcon seems as little capable of dissolving vegetables ; yet the eagle dissolves bread and bone equally; and wood-pigeons may, in like manner, be brought to live, and even to thrive, on flesh meat. The procellaria pelagica, or stormy petrel, lives entirely on oil, as the fat of dead whales and other fishes, whenever he can get it, and if not, converts every thing he swallows into oil. He discharges pure oil from his mouth at objects, that offend him; and feeds his young with the same substance. This is the most daring of all birds in a tempest, though not more than six inches long. As soon as the clouds begin to collect, he quits his rocky covert, and enjoys the gathering and magnificent scenery: he rides triumphantly on the whirlwind, and skims with incredible velocity the giddiest peaks and deepest hollows of the most tremendous waves. His appearance is a sure presage of foul weather to the seaman.

There are some tribes of animals that appear capable of subsisting on water alone, and a few on mere air, incapable as these substances seem to be, at first sight, of affording any thing like solid nutriment. Leeches and tadpoles present us with familiar proofs of the former assertion, and there are various kinds of fishes that may be added to the catalogue. Rondelet kept a silver fish in pure water alone for three years; and at the end of that period it had

• Home, On the Ġizzards of Grazing Birds, Phil. Trans. 1810, p. 183

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