402 



GENERAL SCIENCE 



diets, but their digestive organs are so modified that they 

 easily take care of large quantities of waste materials, 

 such as cellulose, which forms the indigestible walls of 

 plant cells. The digestive organs are intended for work, 



Wheat 



Turnip 



Corn 



Apple 



FIG. 357. Nutritive Values of Different Foods. 



Fats, black ; carbohydrates, horizontal lines ; proteins, vertical lines ; other 



parts, water. 



but they should not be overworked in separating from 

 food an excess of poisonous wastes. 



Principles of Cooking. Man is the only animal 

 that cooks his food, although a number of animals will 

 eat cooked food. Cooking renders food more digestible 

 or more palatable; and either is a sufficient reason for 

 the extra trouble. With the exception of fruits only a 

 few articles of food are eaten in their natural state. 



Cooking has a marked effect on meats. Raw meat 

 is tough and not easily pulled apart. Cooking breaks 

 up the connective tissue and causes the muscular fibers 



