392 THE METABOLISM OF THE PURIN BODIES 



xanthin and hypoxanthin. The following structural formulae de- 

 monstrates the chemical relationship of these bodies : 



6 NH-CO N = C-NH 



I II II 



C 2 C 5 - HN? CH - C - NH CH C - NH 



I I /C 8 H "I ^CH II II \CH 

 HN 3 - C 4 - HN 9 / N - C - N/^ N - C - N<^ 



Purin Hypoxanthin Adenin 



(6 oxy-purin) (6 amino-purin) 



HN - CO HN - CO HN - CO 



II II 



CO C-NH C(NH)C-NH CO C - NH 



I 'I \CH I " >CH I II \CO 



HN - C - N-^ HN - C - N^ HN - C - NH/ 



XantJiin Guanin Uric acid 



(2-6 di-oxy-purin) (2 ammo 6 oxy-purin) (2-6-8 tri-oxy-purin) 



CH 3 -N-CO CH 3 -N-CO 



II II /CH 3 



CO C-NH CO C-N 



I II CH 



CH 3 - N - C - N CH 3 - N - C - N 



Caffein or thein Theobromine 



(1-3 di-methyl-hypoxanthin) (1-3-7 tri-niethyl-hypoxanthin) 



The atoms in purin are numbered so that we can indicate in the 

 formulae of the other members of the group the exact position of 

 side groups. 



We are now in a position to proceed with the metabolism of 

 the purins. 



In the case of mammals, the metabolism of the purin bodies 

 is by no means so simple a study as it is in birds. In mammals, 

 the purin bodies are excretory products of only secondary im- 

 portance in comparison with urea, which forms the chief end 

 product of proteid metabolism. Thus, in mammals, of the total 

 nitrogen excreted each day in the urine about 86 per cent, appears 

 as urea and only 3 per cent, as purin bodies. In birds, on the other 

 hand, the greater proportion of the nitrogen is excreted as purin 

 bodies (uric acid) and only a trace as urea. If uric acid be given 

 by mouth to mammals it reappears in the urine as urea : if urea 

 be similarly fed to birds it reappears in the urine as uric acid. 

 Before proceeding further, let us see wherein lies this difference 



