3. It produces heat and energy.
4. It regulates the body.
How then can we judge if a substance be a food? By deciding that it performs one of these duties in the body.
LESSON II
NECESSARY SUBSTANCES IN FOOD
The names of the substances in food which supply the material for the different uses of the body should be taken next.
1. For building and repairing.—(1) Mineral matter—used largely in hard tissues. (2) Nitrogenous matter, or protein—used largely for flesh. (3) Water—used in all tissues.
2. For fuel.—Carbonaceous matter (starch, sugar, fat).
3. For regulating.—Mineral matter, water.
Note.—The teacher should call attention to the fact that few foods contain all these substances, some have nearly all, some have only one, some two or more. In order to get all, we must eat a variety of foods. The class is now ready to consider the well-known foods, in order to find out which of these necessary substances each food contains, and to obtain a general idea of their comparative food values.