10 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



A considerable variability is thus revealed, the significance of which 

 cannot be definitely assessed. Probably most of it is due to other factors 

 than the functional variability of individual animals. In particular, it 

 seems probable that the individual results represent varying degrees of 

 success in attaining the endogenous level of urinaiy nitrogen excretion, 

 because of the presence of varying amounts of absorbable nitrogen in 

 the rations, or of an inadequate consumption of them. The same situa- 



Note. — It is interesting to note that Petren (J. Biol. Chem., 61:355 (1924)) in the clinical 

 treatment of diabetic patients by means of diets very low in protein and carbohydrates and rich 

 in fat, has obtained extremely low values for the day's excretion of urinary nitrogen. When 

 expressed per kilogram of body weight these values range from 0.023 to 0.035 gms. 



tion exists with respect to similar experiments on men, the results of 

 which are summarized in Table 2. 



It is perhaps significant that in general the lowest values have been 

 obtained with human subjects only after 10 days or more of subsistence 

 upon the experimental diet. The lowest and most recent results were 

 obtained on the 34th and the 71st days of feeding. The slow adjustment of 

 the animal body to low levels of nitrogen feeding, noted in particular by 

 Hindhede(^*), is evidently a similar phenomenon. Apparently the " de- 



