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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 *Wiedemann, Archiv. b. i.
+ Valisnieri, Anatomia, &c. p. 159. 1713.
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 characterised. 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 granivorous. They have also "a swell in the lower part of the œsophagus, 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 sur
rounding 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.
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 M. 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
* Home, On the Gizzards of Grazing Birds, Phil. Trans. 1810, p. 183.
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 wildboar and the vulture devour the rattle-snake 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 seamen.
There are some tribes of animals that appear capable of subsisting on water alone, and a few on mere