NUCLEIN OR PURINE METABOLISM 879 



allowed to act upon uric acid it splits off the right-hand group, forming 

 urea and a body known as alloxan. 



NH CO NH CO 



CO C NHx CO CO NH 2 \ 



| || >CO + H 2 + 0^ | | + '>CO 



NH C XR/ NH CO NH/ 



Further oxidation converts the alloxan into parabanic acid, 

 NH CO 



CO 



and C0 2 , 



* 

 NH CO 



and parabanic acid by hydrolysis is finally converted into oxalic acid, 



CO OH 



and urea. 

 CO OH 



Potassium permanganate, on the other hand, attacks the central 

 3-carbon chain at once, forming allantoin. 



NH CO NH 2 



CO CO and C0 2 . 



NH CH NH 



From the allantoin by processes of oxidation and hydration both urea 

 groups may be split off as before. 



If uric acid be given to a man there is no proportional increase of 

 the uric acid in the urine. It has been shown by Schittenhelm that 

 many tissues contain uricolytic ferments which have the property of 

 breaking down and oxidising uric acid. This oxidation may be 

 complete or incomplete. In the former case the uric acid administered 

 will appear in the urine simply as urea. In the latter it may appear 

 as one of the products already described, e.g. oxalic acid or allantoin. 

 In the dog uric acid is practically absent from the urine, allantoin 

 taking its place, and uric acid administered to this animal gives rise 

 to a corresponding but not equal increase in the allantoin of the urine. 



EXCRETION OF URIC ACID 



The complexity of these various processes in man renders it a 

 difficult task to form a clear idea of the origin of the urinary uric 

 acid and of the conditions which determine the variations in the amount 



