URIC ACID AND THE PURINE BODIES 645 



cretion of uric acid instead of urea. Everything which in a mammal 

 tends to cause an increase in urea excretion causes in birds and reptiles 

 a similar increase in the excretion of uric acid. 



In the early days of research in the uric-acid problem, not inconsid- 

 erable mistakes were made on account of failure to recognize the essen- 

 tial difference in the metabolism of uric acid in birds and mammals, 

 and the tendency for some time after the exact state of affairs was 

 discovered was to consider that in mammals none of this synthetic proc- 

 ess occurs. The latter view, however, is surely incorrect, for a cer- 

 tain amount not only of uric acid itself but of the lower purine bodies 

 can be produced by synthesis in the mammalian body. Thus, Ascoli and 

 Izar 47 discovered that uric acid could be made either to disappear or 

 to be formed when a minced preparation of liver was incubated, depend- 

 ing upon whether oxygen or carbon dioxide was bubbled through it. 

 With oxygen uric acid disappeared, whereas with carbon dioxide uric 

 acid accumulated, indicating that in the presence of this gas the destroyed 

 uric acid became reformed from the disintegration products of the oxy- 

 genation process. As similar results were obtained from the livers of 

 birds, it is clear that no essential difference exists between the purine 

 metabolic processes occurring in the livers of birds and of mammals. 

 The difference is a quantitative not a qualitative one. 



Regarding the chemical nature of the product into which uric acid is 

 broken down and from which it may be resynthesized, it has been pos- 

 sible so far to identify but one substance namely, dialuric acid. This 

 is a perplexing result, for from all other investigations it would appear 

 that in mammals, with the exception of man and the anthropoid apes, 

 uricase splits uric acid into allantoine (see page 640), which substance, 

 however, when added to liver extract did not cause any uric acid to be 

 formed ; nor did any of the other known decomposition products of uric 

 acid have such a result. The chemical reaction involved in the produc- 

 tion of uric acid from dialuric acid and urea is indicated as follows: 



NH C = O 

 '/ \ 



J 



\ 



(dialuric acid) (urea) 



The synthesis of uric 'acid is brought about by the combined action 

 of a thermolabile enzyme in the blood and a thermostable body in the 

 tissues. An aqueous extract of blood-free liver of the dog can destroy 



