THE PROTEIN REQUIREMENTS OF MANKIND 99 



carbohydrates and fat of dietaries, may not give anything like 

 accurate results. 



This objection does not hold when dealing with protein. The 

 faecal nitrogen may be accepted as a true measure of the protein 

 lost to the body, whatever may be the actual form in which it is 

 excreted. Thus, in conditions of excessive putrefaction, the 

 nitrogen may be largely represented as masses of bacteria. 

 However, as nitrogen cannot be lost nor created in the bowel, 

 any change of form will have no influence on the actual quantity 

 present. One other point in this connection may be referred to 

 viz., the nitrogen eliminated in the faeces that really has been 

 metabolized, but has been made use of in the formation of the 

 intestinal juices. There is very little doubt that vegetable 

 dietaries, such as those of India, require a very much greater 

 secretion of the several digestive juices than the ordinary mixed 

 dietary of Europeans, and that relatively there is a greater 

 loss of metabolized nitrogen from this source than should be the 

 case. 



Strictly speaking, the nitrogen derived from the secretions 

 of the bowel is not really loss from the protein intake of the food, 

 but in actual effect it comes to exactly the same thing. Whether 

 the faecal nitrogen is derived from the protein of the food or from 

 the intestinal secretions, it is lost so far as the body is concerned. 

 If a diet requires great quantities of the intestinal juices for its 

 digestion, a corresponding great increase in the faecal nitrogen 

 from this source will be determined, and a corresponding amount 

 of nitrogen will be withdrawn from the body to provide the 

 materials necessary for the digestive secretions. We have, 

 therefore, in the determination of the f secal nitrogen a true measure 

 of the total waste of protein corresponding to the dietary for the 

 period during which the investigation is being carried out. With 

 a knowledge of the protein intake during that period the co- 

 efficient of protein absorption from the food can easily be 

 arrived at. 



Having decided that dietaries may be considered from the 

 view-point of their total protein and energy values, and that the 

 potential energy is usually sufficient, if not excessive, the only 

 question we are directly concerned with at present is the protein 

 element. 



