ALIMENTATION 109 



supply can be determined as well as the quantity of carbon 

 dioxide produced. It also permits the measurement of the 

 amount of heat produced by the subject which, when supple- 

 mented by analysis of the urine and feces, gives the total carbon 

 and nitrogen excretion along with the heat loss. Since the 

 amount of protein, fat, and carbohydrate oxidized in the body 

 may be determined from the carbon and nitrogen excretion, the 

 amount of foodstuffs necessary to meet these requirements can 

 be calculated; and since there is a close correspondence in the 

 estimated and actual food requirements, a satisfactory proof is 

 reached that the energy released as heat, or as heat and work, 

 is derived from the potential energy of the food stuffs eaten. 



The basal metabolism refers to the amount of heat produced 

 when the body is at rest. On the average this amounts to about 

 1,600 calories for a man and about 1,400 calories for a woman, 

 during a 24-hour period. If the subject in the calorimeter 

 performs active work on a bicycle ergometer, the total energy 

 produced as heat and muscular work may be increased to over 

 5,000 calories. The dietary requirements vary in proportion 

 to the total energy requirements. 



Foods. — Animals use food closely allied in chemical composi- 

 tion to animal tissues. Foodstuffs, except water, cane sugar, 

 and sodium chloride, are not ordinarily used as separate articles 

 of diet. Any single article of food, such as rice or meat, may 

 contain all the foodstuffs, yet rice is thought of as a carbohydrate 

 food and meat as protein food, because of the relative pre- 

 dominance of carbohydrate in rice and of protein in meat- 

 Protein exists in various forms, such as the myosin of meat, 

 casein of milk, gluten of bread, and albumin of eggs. Carbo- 

 hydrate foods, such as rice or whole-wheat flour, contain a high 

 percentage of starch. Carbohydrate in the form of sugar is 

 obtained principally from fruits or in a pure form, usually as cane 

 sugar. A variable amount of fat is found in meat, fruit, and 

 vegetables. In diets this is usually supplemented by additional 

 fat in the form of butter or vegetable oils. Water and inorganic 

 salts are constituents of all foods. 



Vitamins. — In addition to protein, fat, carbohydrate, water, 

 and inorganic salts the animal body requires minute amounts of 

 organic substances known as vitamins. A number — at least 

 six — have been identified, though not completely isolated in a 



