180 NUTRITIONAL PHYSIOLOGY 



The Eskimos necessarily eat but little carbohydrate, for 

 they can obtain no vegetable food of importance; it seems 

 plain, however, that they have increased both fat and pro- 

 tein consumption and not protein alone. 



The foregoing suggestions make clear the inconveniences 

 and the unhygienic aspect of any attempt to live on a 

 single type of food. It is a fact, furthermore, that one 

 could not under any conditions continue indefinitely to eat 

 only non-nitrogenous food. Protein metabolism never 

 ceases and a certain nitrogenous income must be provided. 

 We cannot, therefore, judge the fitness of a diet solely by 

 its heat value. It must measure up to a reasonable stand- 

 ard in this respect, but it must also include a suitable pro- 

 portion of protein. Another criterion, not so commonly 

 insisted upon, is that a sufficient quantity and variety of 

 mineral compounds shall be supplied. Of course, these 

 scientific characterizations of the diet are inadequate unless 

 attention is paid also to attractiveness and digestibility. 



When a subject freely chooses his food, unprejudiced 

 by chemical knowledge, he is apt to make use of all three 

 classes of food-stuffs to a considerable extent. Carbo- 

 hydrate will usually amount to more than half the total 

 solids of the ration, while protein and fat show a curious 

 tendency to be taken in nearly equal weights. An 'ex- 

 ample of such a selection, perhaps the one most frequently 

 quoted, is the following: 



Protein 100 grams (410 Calories). 



Fat 100 " 930 " 



Carbohydrate 250 " 1025 " 



2365 " 



Of late years, observation having been extended to large 

 numbers of people, it has become evident that Americans 

 of student and professional classes rarely choose to eat as 

 much as 100 grams of protein. 



Calorimetry. We have been speaking of the amounts 

 of heat set free in the oxidation of various food materials, 

 and of the energy liberated by animals and men as an ac 



