is found in sweet milk. Grape sugar is found in grapes and honey; the small grains seen in raisins consist of grape sugar; it can also be prepared artificially from starch. Cane sugar is found in cane, in sap of the maple, and in the sugar beet (Exps. 2, 3).
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Fig. 88.—A Tiny Bit of Potato, highly magnified, showing cells filled with grains of starch. Cooking bursts these cells.
Fats include the fats and oils found in milk, flesh, and plants. A fat, such as tallow, is solid at the ordinary temperature; while an oil, such as olive oil, is liquid at the same temperature. Tallow was oil while it was in the warm body of the ox. Sugar is transformed into fatty tissue as readily as is fatty food itself.
Proteids are the only foods that contain the tissue-building nitrogen. Protoplasm cannot be formed without nitrogen. We do not often see a pure proteid food, for this food stuff is not so readily separated from foods containing it as are starch, sugar, and fat. Albumen, or white-of-egg, is proteid united with four times its weight of water. Pure proteid is also called albumin. Coagulation by heat is one test for proteid (Exp. 4). These are the names of proteids, or albumins, found in several common foods: casein, the curd or cheesy part of milk; myosin of lean meat; fibrin in blood; legumin in beans and peas; gluten, or the sticky part of wet flour; gelatin in bones. Proteid is valuable to the body as fuel
