On the other hand, those animals which are enormously fat, live exclusively upon vegetables, and drink largely. The hippopotamus, for example, so uncouth in form from its immense amount of fat, feeds wholly upon vegetable matter--rice, millet, sugar-cane, &c. Naturalists long entertained the opinion that this animal, living mostly in the water, fed chiefly upon fish. It is now, however, well ascertained that the hippopotamus never touches fish, and is wholly a vegetable feeder. The walrus, which, according to Buffon, seems to afford the connecting link between amphibious quadrupeds and the cetacea, is a veritable mass of fat, and lives exclusively upon marine herbage. The walrus of Kamschatka measures from twenty to twenty-three feet in length, sixteen to eighteen feet in circumference, and weighs from six to eight thousand pounds. The following fact may be cited as a remarkable proof that the quantity of fat in any animal is mainly dependent on the character of its food: Among the whale tribe, those monsters in size, that of Greenland (Balæna mysticetus of Linnæus) possesses the greatest amount of blubber, and it feeds upon zoophytes, of which many resemble as much in character the plant as the animal. The fin-backed whale (Balæna böops of Linnæus), which does not feed upon mucilaginous matter, but upon small fish, has a much thinner layer of blubber than the former. The sperm whale or cachalot (Balæna physalus of Linnæus), which feeds on mackerel, herrings, and northern salmon, although nearly as long as the Greenland whale, is much thinner. The layer of blubber is not so thick as in the fin-backed, and yields only ten or twelve tuns of oil; while the Greenland whale yields fifty, sixty, and even eighty tuns. Now, chemistry, as we have said, furnishes a rational explanation of these facts. With the exception of flesh, all alimentary substances (the mucilaginous, the gummy, the saccharine, the aqueous, &c.) consist of carbon and hydrogen, and fat is composed of the same elements. Success in the treatment of disease would be more frequent, if medical practitioners would pay greater attention to the chemistry of the vital functions; and the reason why certain articles of diet have a greater tendency than others to the formation of fat, would, by the aid of the exact science of chemistry, be rendered self-evident.