Aliment, Or Food, all the solid and liquid substances requisite for the nourishment of the body. The living body is in a constant state of change. Every one of its motions, every exertion of the voluntary muscles, even the contractions of the heart and the movements of respiration, are attended by the disintegration of some portion of the tissues, which must be renovated in order to maintain their vital activity. This constant waste of tissues demands a corresponding supply of food, by which the loss may be made good. Properly speaking, all the ingredients of the body constantly require to be replaced, and must therefore form a part of the food. Alimentary materials are accordingly divided into groups, distinguished from each other by certain characteristics. 1. The first comprises the inorganic substances proper, namely, water and the mineral salts. They are all essential as ingredients of the food, since they form an essential part of the bodily frame. Of these inorganic substances, water is the most abundant and the most constantly indispensable. It forms from two thirds to three quarters of the entire mass of the human body, and is constantly discharged from the body by the perspiration, the respiration, and the urine.

The water thus lost must consequently be replaced by that which is taken with the food and drink. The quantity of water taken in to supply the wants of the system is for an adult man, on the average, about 4 1/2 pounds per day. Of the mineral salts which are necessary constituents of the body and of the food, chloride of sodium, or common salt, and phosphate of lime are the most important. They exist in greater or less abundance in every one of the solids and fluids of the body. Chloride of sodium, for example, is present in the blood in the proportion of 4 1/2 parts per thousand; and phosphate of lime exists in the bones and other solid tissues in much greater proportion. Both these substances are also ingredients of the food. Chloride of sodium is found in muscular flesh, or lean meat, in the proportion of two parts per thousand, and we are also in the habit of adding it to the food as a condiment. Breeders of sheep, cattle, and horses always find that a liberal supply of common salt improves greatly the condition of the animals. Phosphate of lime exists in the muscular flesh of animals, in fish, oysters, eggs, in the cereal grains, in peas, beans, potatoes, beets, turnips, etc, and even in most of the juicy fruits.

The alkaline salts, the carbonates of soda and potassa, are also necessary to the nourishment of the body; since the blood and most of the secretions must have an alkaline reaction, and this reaction is for the most part communicated to them by the presence of the carbonates of soda and potassa. Unlike the mineral salts, however, the alkaline carbonates are not usually introduced into the body under their own form. Many of the summer fruits and vegetables contain salts of soda and potassa combined with various organic acids, such as the malates, tartrates, and citrates of these bases. These salts are decomposed in the interior of the body, and their vegetable acids replaced by the carbonic acid. Thus they become alkaline salts, and provide for the proper constitution of the animal fluids. 2. Another group of the alimentary substances comprises starch and sugar. These two resemble each other in their chemical constitution, being composed of carbon, hydrogen, and oxygen alone. They are further connected by the fact that starch may by various means be converted into sugar. The readiest mode of doing this is perhaps by boiling with a dilute acid.

If 320 grains of starch be boiled for five hours with about two fluid drachms of sulphuric acid in a pint of water, it will be found to have lost the properties of starch and acquired the sweet taste and other characteristic qualities of sugar. There are various other modes by which the same change may be accomplished; and in fact in very many instances, if not in all, in which sugar is formed in the juices of vegetables, it has first appeared in the form of starch. Of the substances belonging to this group, the different varieties of starch are the most abundant. Starch is found, in the form of minute rounded grains, in a vast number of vegetable productions. It is abundant in wheat flour, in rice, Indian corn, rye, barley, oats, potatoes, peas, and beans, and enters in smaller proportion into nearly every article of vegetable food. In the process of cooking, or heating the starch in contact with water, its grains swell up, become softened, absorb water, and at last, if the heat be sufficiently long continued and the water sufficiently abundant, they fuse together into a gelatinous, homogeneous mass. In this condition they are much more digestible than in the raw state, and it is in this form that starch is almost always actually used as food.

Sugar is also taken not only in its purified form, as an addition to other substances, but also as a natural ingredient in the sweet juices of nearly all the i fruits and most vegetables. Wheat flour contains 5 per cent. of sugar, milk nearly 5 per cent., beets 9 per cent., pears over 10 per cent., and peaches and cherries from 16 to 18 per cent. Vegetable substances containing starch and sugar are always useful, and in the long run indispensable for maintaining health in the human species. A diet exclusively composed of meat and other animal substances becomes after a short time exceedingly distasteful, and an almost irresistible desire is experienced for food of a vegetable origin. This is an instinctive demand of the system. Even dried or preserved vegetables will not answer the purpose indefinitely, for there is something in the fresh vegetable juices winch is essential to health; and if fresh vegetables are excluded from the food for a long time, all the symptoms of scurvy begin to manifest themselves, showing a generally disordered condition of the nutritive func-tions. 3. A third group of alimentary ma-terials comprises the fats.