406 THE METABOLISM OF THE PURIN BODIES 



estimating the purin contents of an organ it is of importance, 

 therefore, to determine independently the combined and the free 

 purins. It would be beyond the scope of this article to describe 

 the methods used for these estimations ; the details are fully given, 

 and the accuracy of the methods proven, in a recent paper by 

 Burian and Walker Hall ( 12 ). Of importance for our purpose, 

 however, are the results obtained for different animal food-stuffs. 

 These are given in the following table. 



TABLE III 



100 Grin. Flesh Substance contain: 



Only in the case of flesh and thymus gland is the proportion 

 of free to nuclein purins given. It will be noticed that in flesh 

 most of the purin is present in a free state as xanthin and 

 hypoxanthin, whereas in thymus most of it (adenin) is combined. 

 The methyl-purins represented by the alkaloids caffein, thein, 

 and theobromine must also be reckoned as purin- containing food- 

 stuffs. 



As already pointed out, in estimating the purins in the urine, 

 a distinction has to be made between the completely oxidised 

 purin uric acid, and the less completely oxidised basic bodies 

 xanthin and hypoxanthin. This is necessary, as it is, on a priori 

 grounds, improbable that the three groups of purins, the oxy- 

 purins (xanthin and hypoxanthin), the amido-purins (adenin and 

 guanin), and the methyl-purins (caffein, &c.), will all undergo 

 the same changes in the organism and be excreted in the 

 urine in the same form. To convert the oxy-purins into uric 

 acid, oxidation alone has to occur, but before oxidation of the 



