396 



ere ted by the kidney, and thus excessive work is thrown upon 

 these excretory organs. 



It is therefore not advantageous to adopt a too purely protein 

 diet. The great use of proteins is as muscle-builders. When 

 the muscles are in a state of constant activity they have a 

 certain power of laying on protein as they grow. Hence the 

 value of proteins in muscular training. 



Gelatin, although undergoing digestion and absorption like 



PROTEIN 



FIG. 162. To show the effects on the metabolism of proteins and fats of feeding 

 a fasting animal. The continuous horizontal lines indicate the amount 

 of material metabolised, the broken horizontal lines the amount taken. 

 The differences between the levels of these indicate the amount of protein 

 and of fats of the animal body which are metabolised. The first column 

 represents the condition in fasting the succeeding columns the intake and 

 output each day when food is given. 



the proteins, is not available as a muscle- builder. Its sole 

 use is as an energy yielder, and in this respect it has a value 

 equal to the proteins. 



Carbohydrate Diet. Carbohydrates are of equal value with 

 proteins as a source of energy, but they contain no nitrogen, and 

 they are not available alone for building up and repairing the 

 protoplasm of muscles and other tissues. Carbohydrates alone 



