THE METABOLISM OF THE PURIN BODIES 411 



leading question can be answered : from it we see that, in the 

 dog at least, feeding with thymus gland and with hypoxanthin 

 raises the exogenous excretion to the same extent as does the 

 subcutaneous injection of an equivalent amount of uric acid. 

 Now adenin, the purin in thymus nuclein, differs from hypo- 

 xanthin in having an amido group in place of oxygen (see p. 392). 

 Since both adenin and hypoxanthin are easily oxidised into uric 

 acid, and all the three, i.e. adenin, hypoxanthin, and uric acid 

 itself, raise the purin excretion to the same extent, it is highly 

 probable that in the blood they are all converted into the same 

 substance, viz. uric acid, which is then partially destroyed. In 

 other words, any oxy- or amido-purin, in whatever way it 

 gets into the systemic blood of the dog, is probably converted 

 into uric acid, 1 of which one-twentieth part (5 per cent.) is 

 excreted unchanged in the urine. We must naturally assume, 

 then, that the endogenous purin bodies, produced by nuclein 

 disintegration or from the muscles, will be excreted in the 

 urine to the same extent. If experiments of this type be 

 repeated at different periods on the same dog. or on different 

 dogs, similar results will invariably be obtained, one-twentieth 

 to one - thirtieth of the uric acid present in the blood being 

 excreted in the urine ; and this is true from whatever source, 

 i.e. exogenous or endogenous, the uric acid is derived. Sub- 

 cutaneous injection, feeding with hypoxanthin or with nuclein 

 and decomposition of tissue nuclein, all yield the same result ( 32 ). 



In cats, Mendel and Brown ( 17 ) found that of pancreas punn-TV 

 4-5-5*7 per cent, reappeared as uric acid-^V in the urine ; figures, in 

 general, very like those which Burian and Schur obtained for dogs. 2 



If, then, the actual uric acid excretion in these animals 

 (cats, dogs) be multiplied by 20-22, the product will represent 

 the total amount of uric acid produced in the tissues. This figure 

 Burian and Schur call the integral factor for purin excretion. 3 



1 This is brought about by an oxidising ferment, xanthin-oxydase. Uric acid 

 given by the mouth is all converted into urea. 



2 Intravenous injection cannot be employed for the experiments because 

 it produces profound depression. 



3 Kanger( 31 ) has recently tried to make out that in cats the amount of uric 

 acid excreted bears no numerical relationship to the amount of uric acid given 

 in the food. If, however, his results be calculated out on Burian and Schur's 

 method, they will be found to agree very well with the laws formulated by these 

 workers. This is true until a dose of '5 grin, uric acid is given, when poisoning 

 symptoms appear. 



