THE METABOLISM OF THE PURIN BODIES 403 



that this constancy in the amount of endogenous uric acid on 

 changing from a purin-free diet of high nitrogen value eggs 

 and cream to one of low nitrogen value starch and cream 

 is not so marked as Burian and Schur state it to be. In 

 several of the investigations recorded by Folin, the change in 

 endogenous uric acid following the change of diet was indeed 

 very slight, but in two cases it was quite marked. This worker, 

 while accepting in general Burian and Schur' s contention, would, 

 therefore, not consider it as infallible. In other observations 

 recorded by Folin, it was noted that on changing from a pure 

 starch diet to one of potatoes a very distinct increase in the 

 endogenous uric acid excretion occurred. This would seem to 

 show that the amount of purins in potatoes, though quanti- 

 tatively small, is yet sufficient to influence the exogenous 

 excretion. 



Burian and Schur have collected together, from the literature 

 a considerable number of estimations of the endogenous purin 

 excretions by this direct method, and have found that it may vary 

 considerably in different individuals. Taking all the results hitherto 

 obtained, Burian and Schur give the following figures : 



0'12 grm. purin nitrogsn as lowest endogenous quotient (4 cases). 

 0-16 (10 cases). 



0-20 (4 cases). 



These " levels " do not depend on any known physiological 

 condition of the individual. Walker Hall ( 13 ) has tried to show 

 that body weight and endogenous purin excretion ran parallel, 

 but, even from his tables can no simple relation be seen. 

 It is possible, however, that it may depend on muscle weight, 

 for, as we will see later, much of the endogenous moiety pro- 

 bably comes from the muscles. Nor does the average daily 

 level bear any relation to the amount of work which is per- 

 formed, provided this be neither too excessive nor too slight. 

 We have already seen it to be uninfluenced by the diet, pro- 

 vided this be purin-free and sufficient in amount to prevent 

 starvation. 1 



1 It should, however, be pointed out in this connection that the purin excretion 

 is not so large in complete starvation as when proteids alone are withheld in the 

 diet. 



