NUTBITION 227 



up by far its largest constituent, 1 but there is no ground 

 for thinking that this cell protein exists in any other form 

 than as an active constituent of the cell substance. There 

 is no evidence of protein stored simply as reserve to meet 

 future possible protein needs. 



And yet, during starvation, protein is steadily lost from 

 the body, as is shown by the fact that urea and other protein 

 derivatives continue to be eliminated by the kidneys. Nor 

 can this loss of protein be checked by feeding carbohydrates 

 and fats; these may be provided in the food in amounts 

 abundantly sufficient to meet the fuel demands of the body, 

 but without checking the loss of protein. We can only con- 

 clude that the disintegration of protein within the body is 

 an inevitable part of the chemical activity of the cells, and 

 that in the absence of a supply of the protein products of 

 digestion the body takes protein from its own living sub- 

 stance. Hence protein becomes an indispensable article of 

 diet. The student will, moreover, recall the fact that while 

 carbohydrates and possibly fats may be made from pro- 

 tein, protein cannot be manufactured from the non-protein 

 nutrients. This obviously follows from the fact that fats 

 and carbohydrates are lacking in nitrogen and sulphur, two 

 essential elements of the protein molecule. 



14. Increase of protein in the food increases protein destruc- 

 tion by the body. One peculiarity of the behavior of protein 

 in the body of itself limits the accumulation of any large 

 amount of storage protein. As soon as we increase the protein 

 of the food, there is an increase of protein disintegration in 

 the body, and in a few days protein disintegration equals 



1 The following analysis of muscle cells (lean of meat) is typical : 



Water 75 parts 



Solids 25 parts 



Protein 21 parts 



Salts 1 part 



Fat, connective tissue, etc . . . 2 parts 



Other extractives ,,,,,,, 1 part 



