50 HUMAN BIOLOGY 



kind of food substances that we found in plants ; and this 

 is what we might expect, since the cow is whoUy'dependent 

 upon grass and other vegetable foods. Indeed, when we 

 analyze any other animal foods that we eat, we find that all 

 consist of one or more of the food substances which closely re- 

 semble those that we have been stud3dng in plant biology. In 

 Figures 19 and 20 are represented not only the various nu- 

 trients found in some of our most common foods, but also 

 their relative proportions in percentages. 



52. Composition of various foods. — (Home study.) 



1. Name the foods represented in Figures 19 and 20 that are 



derived from animals; name those obtained from 

 plants. 



2. Which of the two classes of foods, named in 1 above, has 



on the average the larger percentage of protein? 



3. In which of these two classes do you find the larger 



amount of fats ? 



4. Which class has the larger percentage of carbohydrates? 



5. What, then, are the principal differences in the composi- 



tion of animal and vegetable foods ? 



6. Name the various food substances found in one animal 



food and in one vegetable food, giving in each case the 

 percentage of each nutrient. 



IV. Uses of the Food Substances 



53. Uses of the food substances to plants and animals. — 



In our study of green plants we learned that these living 

 organisms can manufacture the food substances they need 

 from the simple compounds (water, carbon dioxid, and 

 mineral matters) found in earth, air, and water, and that 

 these food substances are used for the making of protoplasm 

 and the liberation of energy. Animals and human beings, 

 on the other hand, since they cannot make their foods, are 



