FOOD. All substances susceptible of dioestion and assimilation may come under the denomination of, ood ; but the proximate principles of organic bodies on which their nutritive powers depend are comparatively few. Hence, although, the articles employed in different countries for the support of animal life are almost infinitely various, their sustaining powers may be referred to certain substances capable of being separated and identified by chemical analysis and tests. Among the proximate elements of vegetable food gluten and its modifications, starch, gum, sugar, oil, wax, and lignin or woody fibre, are by far the most important ; and among those of animal food albumen, gelatin, and their modifications, together with fiats and oils, which are common to both kingdoms of nature.
To illustrate the actual simplicity of our food as compared with its apparent multi fariousness and complexity, it may suffice to state, that wheat and almost all the esculent grains consist principally of starch and gluten; that the same ingre dients are found in many fruits and roots ; that sugar, gum or a relation of gum which is called vegetable jelly, together with minute traces of aromatic principles which give flavor, and more or less abundance of water, and of vegetable acids, are the chief component parts of apples, pears, peaches, currants, gooseberries, and all analogous tribes of fruits ; a very few also contain oil. Then, as regards animal food, the muscular fibres of various ani mals closely resemble each other in com position and nutritive power ; in some cases texture merely, and in others mi nute additions of foreign matters, confer upon them their relative digestibilities, and their different aspects and flavors; albumen or fibrine, and gelatin, small proportions of saline bodies, and a large quantity of water are found in them all. It often happens that the truly nutri tious part of food is so combined with or protected by indigestible matters, as to escape the solvent powers of the stomach, unless previously prepared and modified by various chemical and mechanical agents. Indurated woody fibre, for in stance, or lignin, as chemists call it, will often resist the joint action of the stomach and bowels, and pass through the ali mentary canal with scarcely any altera tion. The husks of many seeds and
fruits are composed almost exclusively of this material. This is the case with the kernels of the apple, pear, &c.; the seeds of the currant, gooseberry, melon, and so on ; the skin or husk of peas, beans, &c., and of wheat, barley, and oats ; so that unless the woody part is either broken down by the teeth or previously removed, the food which it envelops is protected from the solvent action of the secretions of the stomach. This is in some respects a wise and curious provision in nature; for birds in this way become the carriers of seeds, which pass through them not only undigested, but even retaining their vegetative powers and in this way un inhabited and sterile portions of the globe may gradually become clothed with verd ure, and shrubs, and trees.' Bones are highly nutritive ; but unless broken into very small fragments by the masticatory powers of the animals which eat them, they too would elude digestion. In refer ence, to the food of man, much of its digestibility and nutritious power is referable to the important chemical operations preparatory to its use which are carried on in the kitchen ; in other words, cookery is essentially a chemical art ; and substances totally unfit, in their raw state, for reception into the stomach, are ren dered palatable, digestible, and nutritious by the skill of the cook. And here salt, and a variety of condiments, as they are called, and which are aromatic and stimu lant substances, chiefly of vegetable ori gin, play an important part ; nor must the mere effect of heat be overlooked, for it is most important. Meat, by boiling and roasting, is not only softened in its fibre, but new substances are generated in it. Among these a peculiar extractive matter, and osmazone, or the principle which gives an agreeable flavor and odor to dressed meat, are especially recognized. Nor are the changes which vegetables suffer under the influence of heat less obvious.