FOOD, any substance which, taken into the body, is capable of sustaining or nourishing, or which assists in sustain ing or nourishing the living being. Foods may be classed under three heads, gase ous, liquid, and solid, the first two con sisting of the air we breathe—the oxygen of which is so essential to life—and the water we drink. Milk, tea, coffee, cocoa, etc., are popularly called liquid food, but each of these is simply water in which various solid substances are dissolved, or held in suspension. The solid foods are of three kinds — viz., nitrogenous, non nitrogenous, and mineral. Nitrogen compounds, or flesh formers, are essen tially composed of carbon, hydrogen, oxygen, and nitrogen. They possess the only ingredients capable of building up and repairing the nitrogenous tissues of the body, but they also furnish a limited supply of heat, especially when heat-giv ing compounds are deficient in the body. Nitrogenous compounds are found both in the animal and vegetable kingdoms under the forms of albumen, fibrin, casein, gelatine, and chondrin. Non-nitrogenous compounds, or heat givers, sometimes called carbonaceous compounds, are com posed of carbon, hydrogen, and oxygen. They serve to keep up the heat of the body, and so produce energy or force; but they contribute, also, to the repair and growth of the body. The chief heat
givers are starch (abundant in the cereal grains), sugar, and fat. None of these substances will of itself sustain life. The mineral foods are the salts of soda and • potash the phosphates of lime and mag nesia, iron, ron, etc. As the daily waste of the body must be met by a daily supply of nourishment, it becomes of the utmost importance that such supply should con sist of both flesh formers and heat givers, and in the proportion of two parts of the former to six of the latter. The National Pure Food Law, which went into effect in the United States Aug. 1, 1900, was aimed against ADULTERATION (q. v.). See NUTRITION; CONSERVATION OF FOOD.
The food of animals is not directly de rived from inorganic nature, but medi ately through the agency of plants. Plants can feed on and assimilate inor ganic matter, in this respect differing from animals. A few plants, however, such as fungi, the sundew (Drosera), and Venus' fly trap, require animal food. The ordinary food of plants con sists of carbon, water, and nitrogen.