362 PKACTICAL PHYSIOLOGY 



weighed out. Carefully gauge the amounts so as to gain an idea of 

 the food necessary daily for a person doing light muscular work. 



For persons leading a sedentary life only 2,500 to 2,700 calories are 

 required. For moderately hard muscular work it is well to allow 

 3,3003,700 C., for hard and very hard muscular work from 4,150 

 5,000 C. are required. Specimen diets are given in the following table: 



Protein. Fat. Carbohydrate. Calories. 



Sedentary, ... 88 108 345 2,501 



Moderate hard work, - {}* |g 476 3,364 



Verv hard W or k , - .{J jg g Jg 



Most investigators have given diets fairly closely resembling these ; 

 and although some of them include more fat than the specimen diet we 

 have taken, it must be remembered that fat is considerably dearer as 

 an article of food. 



Chittenden, as the result of his experiments, believes that the body 

 is better with a low protein diet that is considerably less than those 

 given above. It has recently been shown, however, that the con- 

 stituent parts of the protein vary considerably in their value for the 

 maintenance of health. The ringed amino-acids (tyrosin, tryptophan, 

 etc.) appear to be the most important. Bodies without these, such as 

 gelatine, cannot support life. Yet if these bodies be added to gelatine 

 or other such inadequate diet (e.g. the products of digestion not con- 

 taining the benzene ring), such addition renders the diet adequate. It 

 is worthy of note, also, that the diet supplied to the young animal 

 contains much protein (caseinogen), rich in such " ringed " bodies. 

 The kind of protein in a diet must, on this account, be taken into 

 account. It would seem therefore that it is well, as the analyses of the 

 diets of different nations show, to have about 125 grammes of protein in a 

 diet in order to ensure an adequate supply of substances from which 

 the organism can select what is needed for its nutrition. 



These facts, too, show us how important it is to know the exact 

 composition of the various food-stuffs, so that we may be in a position 

 to draw up an adequate diet sheet. 



The organic food-stuffs may conveniently be divided into two classes, 

 the animal and the vegetable. 



The Animal Food-Stuffs. One of the most important of these, viz. 

 milk, has been discussed in a separate chapter. Meat and eggs form 

 another important class of animal foods. (See Table, p. 366.) 



Eggs. A hen's egg weighs about two ounces or fifty grammes. The 

 shell forms about 1 2 % of the total weight, and consists mainly of 



