Think of some persons who have taken food every day, and yet as long as you have known them they have not increased in size. What has food done for their tissues? The class must be told that the tissues of our bodies wear out through use, and that food has furnished the material to replace the worn-out parts. What do we say we are doing to clothes when we replace the worn parts? We are mending or repairing them. What does food do for our worn-out tissues? _Food repairs the tissues of the body._ Do not think any more about the tissues of the body. Suppose you had not been able to get any food for several days. In what way would you be different from what you are now? You would not be as strong. Food gives strength or energy by being burned inside the body. There is a fire burning in our bodies all the time we are alive, the fuel being food. What do we require from the fire in our homes? We require heat. The fires in our bodies give us heat also. Any fire gives off both heat and energy. State another use of food to the body. _Food produces heat and energy in the body._ But food does more for the body; it contains substances to keep our bodies in order. Suppose the clock gets out of order and does not keep good time, what does the watchmaker do to it? He regulates it. That is what certain kinds of food do for us. What then is another use of food? _Food regulates the body._ Name the uses of food to the body. 1. It builds the tissues. 2. It repairs the tissues. 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. SOURCES OF FOOD All nature supplies us with food. The three great divisions of nature are animal, vegetable, and mineral, and from each we obtain food, though most largely from the animal and vegetable kingdoms. Animal food is some part of an animal's body or some product of an animal: examples--meat or fish, milk, eggs. Vegetable food is some part of a plant: examples--vegetables, fruit, seeds.