The purposes of food are to promote growth, to supply force and heat, and to furnish material to repair the waste which is constantly taking place in the body. Every breath, every thought, every motion, wears out some portion of the delicate and wonderful house in which we live. Various vital processes remove these worn and useless particles; and to keep the body in health, their loss must be made good by constantly renewed supplies of material properly adapted to replenish the worn and impaired tissues. This renovating material must be supplied through the medium of food and drink, and the best food is that by which the desired end may be most readily and perfectly attained. The great diversity in character of the several tissues of the body, makes it necessary that food should contain a variety of elements, in order that each part may be properly nourished and replenished. THE FOOD ELEMENTS.--The various elements found in food are the following: Starch, sugar, fats, albumen, mineral substances, indigestible substances. The digestible food elements are often grouped, according to their chemical composition, into three classes; _vis._, carbonaceous, nitrogenous, and inorganic. The carbonaceous class includes starch, sugar, and fats; the nitrogenous, all albuminous elements; and the inorganic comprises the mineral elements. _Starch_ is only found in vegetable foods; all grains, most vegetables, and some fruits, contain starch in abundance. Several kinds of _sugar_ are made in nature's laboratory; _cane_, _grape_, _fruit_, and _milk_ sugar. The first is obtained from the sugar-cane, the sap of maple trees, and from the beet root. Grape and fruit sugars are found in most fruits and in honey. Milk sugar is one of the constituents of milk. Glucose, an artificial sugar resembling grape sugar, is now largely manufactured by subjecting the starch of corn or potatoes to a chemical process; but it lacks the sweetness of natural sugars, and is by no means a proper substitute for them. _Albumen_ is found in its purest, uncombined state in the white of an egg, which is almost wholly composed of albumen. It exists, combined with other food elements, in many other foods, both animal and vegetable. It is found abundant in oatmeal, and to some extent in the other grains, and in the juices of vegetables. All natural foods contain elements which in many respects resemble _albumen_, and are so closely allied to it that for convenience they are usually classified under the general name of "albumen." The chief of these is _gluten_, which is found in wheat, rye, and barley. _Casein_, found in peas, beans, and milk, and the _fibrin_ of flesh, are elements of this class.