THE METABOLISM OF THE PDRHST BODIES 399 



Nuclein. 



Albumin. Nucleic acid. 



Carbohydrate (?). Phosphoric acid. Amido-purins. 



The amido-purins contained in nucleic acids of different sources 

 (prepared from different nuclein) vary in their nature. The 

 nucleic acid of the thymus contains mainly adenin, that of 

 the pancreas guanin alone, and that of a salmon sperm both 

 guanin and adenin. The amount and nature of carbohydrate in 

 the molecule also varies considerably. 



Knowing, then, that nuclein contains amido-purin bodies in 

 its molecule, we might naturally assume that feeding with these 

 pur ins in a pure state (i.e. with guanin and adenin) would influence 

 the purin excretion just as nuclein itself does. This is, however, 

 not the case, neither adenin nor guanin having much effect on 

 the purin excretion, at least in dogs, and, in man, so far as they 

 have been tried, only having a doubtful effect. 



The last group of food-stuffs which contain purin bodies are 

 such substances as thein, caffein, and theobromine, which it will 

 be remembered are methyl-purins. These do not raise the ex- 

 cretion of uric acid, when they are given in the food, but, as we 

 shall see later, they do raise that of the purin bases. 



So far, then, we have fairly answered our first question. We 

 have seen that exogenous urinary purins may be derived from 

 certain free xanthin bases, but not from all, and from nucleins. No 

 other nitrogenous food-stuff in any way influences the amount 

 of the urinary purins. We see why it is that the urea and purin 

 excretions cannot be expected to run parallel, for, by feeding 

 with purin -free nitrogenous food in varying amount, the urea can 

 be made to swing up and down at will, the uric acid remaining, 

 meanwhile, absolutely stationary. 1 These facts show us how 

 hopeless it was in the older researches to try and strike a 

 constant average for the normal purin excretion of man ; and they 



1 For t'xarnple, Hess and Schmoll ( 8 ) found no increase in the urinary purins 

 by adding twenty-four eggs to a fixed diet, although the urea excretion rose 

 enormously. 



