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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,* 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 be 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.

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

Phil. Trans. 1772.

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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. The 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 many-plies, 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 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

* Wiedemann, Archiv. b. i.

Valisnieri, Anatomia, &c. p. 159, 1715.

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 racehorse 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 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 granivorou ous. 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 mastication," though essentially lighter.

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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

* Home, On the Gizzards of Grazing Birds, Phil. Trans. 1810, p. 183.

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. Spalanzani 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 Spalanzani 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 afterwards, on killing and examining the animal, or on its regorging them, to be broken off and blunted, without any injury to the 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 Spalanzani, 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 petril, 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 grown as large as the glass globe that contained it. Several species of the carp kind, and especially the gold-fish, have a similar power; and even the pike, the most glutinous, perhaps, of the whole class, will both live and thrive upon water alone in a marble basin.

The bee, and various other insects, derive their nutriment from the nectar and effluvium of flowers. So also does the trochilus genus, or hummingbird, which appears to be the connecting link between the two classes; buzzing like the bee itself with a joyous hum around the blossom on which it lights; and in one of its species, t. minimus, not exceeding it in size, and only weighing from 20 to 45 grains.

Air alone appears sufficient for the support of animals of other kinds. Snails and chameleons have been known repeatedly to live upon nothing else for years.* Garman asserts that it is a sufficient food for spiders; and that though they will devour other food, as fishes will that may be maintained alone on water, they do not stand in need of any other. Latreille confirms this assertion to a considerable extent, by informing us that he stuck a spider to a piece of cork, and precluded it from communication with any thing else for four successive months, at the end of which time it appeared to be as lively as ever.† And. Mr. Baker tells us, in the Philosophical Transactions, that he had a beetle that lived in a glass confinement for three years without food, and then fled away by accident.

The larves of ants, as well as of several other insects of prey, are not only supported by air, but actually increase in bulk, and undergo their metamorphoses without any other nourishment. It is probable, also, that air is at times the only food of the scolopendra phosphorea, or luminous centipede, which has been seen, illuminating the atmosphere, and sometimes falling into a ship, a thousand miles from land.

Amphibious animals have a peculiar tenacity to life under every circumstance of privation; and not only frogs, and toads, but tortoises, lizards, and serpents, are well known to have existed for months, and even years, without other food than water-in some instances, without other food than air.

Mr. Bruce kept two cerastes, or horned snakes, in a glass jar for two years, without giving them any thing. He did not observe that they slept in the winter-season; and they cast their skins, as usual, on the last day of April.‡

Lizards, and especially the newt species, have been found imbedded in a chalk-rock, apparently dead and fossilized, but have re-assumed living. action on exposure to the atmosphere.§ On their detection in this state the mouth is usually closed with a glutinous substance, and closed so tenaciously, that they often die of suffocation in the very effort to extricate themselves from this material.]

In respect to toads the same fact has been ascertained, for nearly two years, by way of experiment; and has been verified, by accident, for a much longer term of time. The late Edward Walker, Esq. of Guestingthorpe, Essex, informed me not long since, that he had found a toad perfectly alive in the midst of a full grown elm, after it was cut down by his order, exactly occupying the cavity which it appeared gradually to have scooped out as it grew in size, and which had not the smallest external communication by any aperture that could be traced. And very explicit, and apparently very cautious, accounts have been repeatedly published in different journals, of their having been found alive, imbedded in the very middle of trunks of trees and blocks of marble, so large and massy, that, if the accounts be true, they must have been in such situations for at least a century.** There is a very particular case of this kind given by M. Seigue, in the Memoirs of the Royal Academy of Paris.††

Encyclop. Brit. art. Physiol. p. 679.
Voyages, Appendix, p. 296. Evo. edit.
Journ. of Science, No. XII. p. 375.

† Monthly Rev. Appx. lv. 494.

§ Wilkinson, Tilloch's Phil. Mag. Dec. 1816.

See Dalyell's Introd. to his Translation of Spalanzani's Tracts, p. xliii. 1803. ** See various instances, Encycl. Brit. art. Physiol. p. 681.

tt Mem. 1731. H. 24. Dr. Edwards, of Paris, has sufficiently ascertained of late, that blocks of mortar, and heaps of sand, are porous enough to admit so much air as is requisite to support the life of lizards, toads, and other amphibials of the batrachian family; but that they all perish if surrounded by mercury, or even water, so as to intercept the air by their being encompassed by an exhausted receiver. In boxes of mortar or sand, however, they live much longer than in boxes plunged under water. The probable cause is, that the air of the atmos

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