EXCKETIONS 



487 



but wholly independent of quantitative changes in the total amount of 

 nitrogen eliminated. It may be observed in the case of the uric acid 

 that when the total amount of protein metabolism is greatly reduced, the 

 absolute quantity of uric acid is diminished, but not nearly in proportion 

 to the diminution in the total nitrogen, and the per cent of the uric acid 

 nitrogen in terms of the total nitrogen is therefore much increased. From 

 these observations Folin pointed out that urea and creatinin stand in 

 marked contrast to each other, since the former is largely exogenous in 

 origin, while the latter is almost entirely of endogenous formation. Uric 

 acid stands in an intermediate position, being about half endogenous and 

 half exogenous under ordinary conditions of diet. 



Since urea is largely exogenous in its origin the amount of its excre- 

 tion in the urine obviously depends upon the protein intake. With the 

 dietary standards of Voit and of Atwater calling for 118 to 125 grams of 

 protein, the urea output should be 30 to 35 grams. Comparatively few 

 healthy adults appear to eliminate as much urea as this at the present 

 time. Probably 25 grams may be taken as more nearly representing the 

 average output of urea in the human adult, although judging from the 

 very extensive data given in the Referee Board reports, many individuals 

 average hardly more than 20 grams, corresponding to a protein intake 

 of 75 to 80 grams. It is obvious, therefore, that the daily excretion of 

 10 to 15 grams of urea by many hospital patients finds explanation as a 

 rule, not in defective kidney function, but in a low protein intake. Even 

 here the urea excretion represents a protein consumption of 40 to 60 

 grams, an amount which Chittenden(6) has shown may quite adequately 

 supply the requirements of the average individual. 



Assuming that the average urea output of the human adult is 25 

 grams, the content of the various nitrogenous constituents with their dis- 

 tribution in the total nitrogen may be represented as given in the table 

 below. With this output of urea the urea nitrogen would probably con- 

 stitute about 85 per cent of the total nitrogen, thus making the figure for 



AVERAGE CONTENT OF THE NITROGENOUS CONSTITUENTS IN THE URINE OF THE HUMAN 



ADULT 



