100 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



pancreas, &c.). It is 2, 6-dioxypurine, its oxygen atoms being 

 attached to the atoms numbered 2 and 6 in the purine nucleus. 



NH-C = NH-C = 



II II 



H-C C-NIL = C C-NHv 



ii ii J-H ii ;>C-H 



N - C -N r NH-C - W/ 



[hypoxanthiiic] [xantliinc] 



Adenine is found in the tissues, blood, and urine. It is obtained 

 from several nucleins, but especially from the nuclein derived from 

 the thymus. It is 6-amino-purine. 



Guanine is also a decomposition product of nucleins, especially 

 of that obtained from the pancreas. Combined with calcium it 

 gives the brilliancy to the scales of fishes, and is also found in the 

 bright tapetum of the eyes in these animals. It is a constituent of 

 guano, and here is probably derived from the fish eaten by marine 

 birds. It is 2-amino-6-oxypurine. 



N = C - NH 2 NH - C = 



H- C C - NH X H 2 N - C C - NH, 



II II >C-H || || 



N-C-N^ N-C- 



[adenine] [guanine] 



Uric acid is 2, 6, 8-trioxypurine. 

 NH - C = 



= C - NH V 



I II >CO 



NH-C - NH/ 



[nric acid] 



The close chemical relationship of uric acid to the purine bases is 

 obvious from a study of the formulae just given. Just as in the case 

 of urea, uric acid, however, may be exogenously or endogenously 

 formed. Certain kinds of food increase uric acid because they con- 

 tain nuclein (for instance, sweetbreads) in abundance, or purine bases 

 (for instance, hypoxanthine in meat) ; the uric acid which originates 

 in this way is termed exogenous. Certain diets, on the other hand, 

 increase uric acid formation by leading to an increase of leucocytes, 

 and consequently increase in the metabolism of their nuclei ; in other 

 cases the leucocytes may increase from other causes, as in the disease 

 named leucocythaemia. The uric acid that arises from nuclear kata- 

 bolism is termed endogenous. Although special attention has been 



