The most favourable physiological condition for the production of fat, in man as in the lower animals, is a large extent of intestinal absorbent surface, the absorbent vessels being proportional in number to the amplitude of the intestinal surface. The intestines, however, are conformable to the nature of the aliment. The intestines are small in the lion, tiger and panther, because their food consists of a small quantity of flesh. The ox, on the other hand, a herbivorous animal, possesses an enormous paunch, to contain the large mass of food, yielding but little nutritive matter; consequently the herbivora must have a larger absorbent surface than the carnivora. The length of the intestinal tract in herbivorous animals is equal to fifteen times the length of the body; in the carnivora the length of the intestines is about three times that of the body; while in the tiger, feeding exclusively on blood, it equals only the length of the animal. In this respect man holds an intermediate position, the intestines being equal in length to about five or six times the height of the individual. This provision of nature is in keeping with the character of his food--partly animal, partly vegetable. It is at his option, however, to modify this natural condition, by living wholly upon meat or wholly upon vegetables. A person whose food is very substantial, but small in quantity (as, for example, meat), does not possess the dilated stomach and intestines of the vegetable feeder, and consequently has a less absorbent surface than the latter. Among animals, we notice that the carnivora have naturally but little fat, scarcely any belly, but an enormous development of muscular power; whilst the herbivora are more or less laden with fat. Among men, it may be noticed that the corpulent shew a preference for vegetable and farinaceous food, and partake largely of water, beer, &c. If we examine this question from a chemical point of view, we obtain the most satisfactory evidence that flesh must be productive of less fat than vegetable matter. The composition of human fat in 100 parts is Carbon 79.000 Hydrogen 15.416 Oxygen 5.584 ------ 100.000 The principal constituents of fat, therefore, are carbon and hydrogen. Again, chemistry teaches that all food not consisting of flesh, such as vegetables, farinacea, sugars, &c., resemble fat, being chiefly composed of carbon and hydrogen; and, still more, that fat exists, already formed, in some vegetable substances, as oil of olives, oil of nuts, and oleaginous seeds. If, therefore, we introduce into the system substances rich in carbon and hydrogen, we must make fat as inevitably as the bee makes honey from its elements contained in the flowers.