410 METABOLISM, NUTRITION, AND DIET 



Folin states this theory as follows: "It is clear that the metabolic proc- 

 esses resulting in the end products which tend to be constant in quantity 

 appear to be indispensable for the continuation of life; or, to be more defi- 

 nite, those metabolic processes probably constitute an essential part of the 

 activity which distinguishes living cells from dead ones. I would therefore 

 call the protein metabolism which tends to be constant, tissue metabolism, 

 or endogenous metabolism; the other, the variable proiem metabolism, I would 

 call the exogenous or intermediate metabolism. 



"The endogenous metabolism sets a limit to the low r est level of nitrogen 

 equilibrium attainable. Just where that level is fixed will depend on how 

 much, if any, urea is derived from the same catabolic processes that produce 

 the creatinin. If this can be determined, we shall have a formula expressing 

 more or less definitely the point of lowest attainable protein catabolism, 

 because at such a point the percentage composition of the urine should be 

 practically constant. The total nitrogen eliminated when this constant com- 

 position of the urine has been reached will indicate the lowest attainable 

 level of nitrogen equilibrium." 



The condition of nitrogenous equilibrium, therefore, is one which may 

 be maintained even if the amount of proteid taken as diet far exceeds the 

 necessities of the economy, the urea being excreted in excessive amount; and 

 the wasteful use of proteid food which is so common may not be attended 

 with harmful consequences, so long as the excreting organs are able to elimi- 

 nate nitrogen from the body. 



It is only in cases of growth, by putting on of flesh, as in growing children, 

 that nitrogen is retained in the body in health, except to a very small amount. 

 According to calculations which have been made, it appears that the body 

 puts on thirty grams of flesh for every gram of nitrogen so retained. 



Proteids as Fat- and as Glycogen-Formers. Proteid food is un- 

 doubtedly a source of energy in the body ; and one can say that such proteid 

 as is, according to Voit's view, metabolized without becoming part of the 

 tissue may be considered a source of energy. If this be true, one might ex- 

 pect that proteids could be metabolized into other forms, such as carbo- 

 hydrates and fats. Bernard long ago stated that proteid was a glycogen- 

 former; that abundant glycogen was stored in the liver when flesh diet was 

 fed, and argued that proteid was the source of the glycogen. The careful 

 work of a number of investigators has not obtained sufficient evidence to 

 clear up this question absolutely, but the weight of evidence is in favor of the 

 view that in the body sugar can be formed from proteids. Whether or not 

 proteid can be metabolized into fat, and stored as such, seems at present an 

 open question, notwithstanding the immense amount of work expended in 

 trying to solve the problem. 



Cramer fed 450 grams of lean meat per day to a cat in a respiration cham- 

 ber for 8 days. The daily excretion of nitrogen was 13 grams, of carbon 



