KINDS OF FOOD 347 



Tuberculosis (consumption) often attacks the joints. 

 At the hip it produces "hip disease." 



The chief injuries to muscles come from either overwork or under- 

 work. Most students take too little exercise, and are content to let 

 others play, while they themselves look on. The body should get 

 daily exercise, best out of doors. One should exercise until he just 

 begins to be a little tired; then he should rest. By gradually increasing 

 the amount of our exercise, all of us can build up vigorous bodies. But 

 exercise is useless unless we have good food, and long hours of sleep, and 

 unless we avoid alcohol and all other harmful stimulants. 



357. Kinds of Food. As the cells of the body do their 

 work, some of their protoplasm is used up, and needs to 

 be replaced. Moreover, as the oxygen of the blood 

 comes to the cells, it "burns up" (oxidizes) some of the 

 cell material to give energy to the cells. There are, 

 therefore, two distinct reasons why we must have food : 



(1) In order to give the cells material for their growth 

 and repair; 



(2) In order to give them energy, so that they can do 

 their work. 



So we may say that anything which gives the body the 

 materials for growth and repair, or which gives it heat or 

 energy, is food. 



In spite of the fact that we eat many foods, we can re- 

 duce the kinds of food to five simple foods, or nutrients 

 (Fig. 277 'a; also Appendix, Table XII). The nutrients are: 



1. Proteids. 4. Minerals. 



2. Carbohydrates. 5. Water. 



3. Fats. 



Proteids are obtained from both animal and vegetable 

 food (cf. 56, 298, and 299). One form of proteids is 



