68 THE PHYSIOLOGY OF PROTEIN METABOLISM 



ing varying amounts of protein. He came to the conclusion that the 

 fully grown human organism, for a short period at least, and without any 

 increase of the caloric intake over the normal, could remain in nitrogen 

 equilibrium with an intake of nitrogen of 4/52 grms. (i.e. 28*3 grms. 

 protein, of which only about 12-5 grms. was in the form of pure pro- 

 tein). If the amount be reckoned per kilo of body weight, then the 

 nitrogen requirement is o - o8 grm., of which only 0^03 grm. requires to 

 be in the form of pure protein nitrogen. This amount of nitrogen is 

 considerably smaller than that which was excreted on the third day of 

 complete starvation by Succi : it was not until the third week of fast- 

 ing that values in any way comparable with the figure of Siven were 

 obtained. It is certainly true that if at the close of a fast the subject 

 be put on a protein-free diet the output of nitrogen an output which 

 may reasonably be taken to represent the real protein catabolism may 

 reach a still lower figure. Thus it was found (89) in the case of Beaut6 

 that the output of nitrogen in the urine on the third day after a fast of 

 fourteen days, when he was fed on a diet of starch and cream, amounted 

 to only 2-84 grms. Landergren (237), Folin (129) and Cathcart (90) 

 have also obtained in the normal individual remarkably low outputs 

 of nitrogen when the subject was confined to a diet rich in carbo- 

 hydrate but practically free from protein. Far-reaching conclusions 

 concerning the actual amount of protein required daily cannot be 

 drawn from such experiments unless it be shown that these positive 

 results are not due to the very short duration of the experiments. The 

 importance which is to be attached to results obtained from feeding 

 experiments of short duration, more particularly those in which the diet 

 lacks one or more of the normal constituents or contains them in ab- 

 normal proportion or form, is still a subject of dispute. 



As regards the uniformity of the protein minimum it may be 

 definitely stated that there is no single minimum common to all 

 men and to all conditions. Rubner (342), Caspari (85) and others 

 also hold firmly to this opinion. Caspari quotes the work of Larguier 

 des Bancels in 1903 in confirmation of this belief in the existence of 

 multiple protein minima. The facts which can be cited against a com- 

 mon minimum are many in number. Thus the caloric value of the 

 diet given influences very definitely the protein minimum intake re- 

 quired by the organism. Again, the nature of the food which is fed 

 with the protein influences very materially the amount of nitrogenous 

 material required, as is shown, for example, in the experiments of Voit 

 and Korkunoff. Then, as Rubner has pointed out, the temperature 

 influences quite markedly the course of protein metabolism. Finally, 



