THE METABOLISM OF THE PURIN BODIES 405 



influence on the amount ; if, however, there be a fundamental 

 change in the mode of life, if there be a much higher or lower 

 caloric exchange in the tissues, then will there be a variable 

 endogenous excretion. After excessive muscular work there also 

 occurs a temporary rise. That the endogenous quotient remains 

 constant under similar conditions is demonstrated in the following 

 table : 



TABLE II 



In these observations by Rockwood the diet, although purin-free, 

 varied considerably in composition at the different periods. 



Having described how the endogenous quotient may be directly 

 determined, and the fundamental characteristics of this portion 

 of purin excretion, we are now in a position to consider what 

 proportion of the purin administered in the food, i.e. exogenous, 

 reappears as such in the urine, and whether this portion which re- 

 appears varies with the kind of purin administered? 



As has been shown above, food-stuffs which contain purin 

 bodies in greatest amount are the cellular tissues (glands) and 

 the muscles. These tissues contain their purin bodies partly 

 in a free state (xanthin and hypoxanthin in muscle) and partly 

 combined in nuclein. It will be remembered, however (see 

 p. 399), that free adenin and guanin seem to exercise a dif- 

 ferent influence on the purin excretion according to whether 

 they are given free or built up into the nuclein molecule. In 



