METABOLISM OF PROTEl?. 583 



of animals the oxidative production of uric acid takeS^^ oxygen 

 any particular organ, but in the tissues in general, includingxy purin, 

 It has been shown that when air is blown through a mixtspval 

 splenic pulp and blood, uric acid is formed from purin bodies alrea'o^ 

 present in the spleen. When the quantity of these is increased by 

 the decomposition of nucleins induced by slight putrefaction, the 

 yield of uric acid is also increased. Uric acid is also formed by the 

 perfectly fresh surviving spleen, liver, and thymus in the presence 

 of oxygen, and the quantity is increased when purin bodies are 

 artificially added. 



[ Sources of the Uric Acid] It is well established that in the bird 

 it arises both from ammo-acids derived from the hydrolysis of 

 protein and from nuclein compounds and their derivatives in the 

 food and tissues. The amino-acids constitute by far the greatest 

 source of uric acid in these animals and in the reptiles, and it is 

 practically certain that the course of the decomposition of the 

 amino-acids and the form in which nitrogen is liberated from them 

 in its transformation into this end-product are not essentially differ- 

 ent from what obtains in the formation of urea in the mammal and 

 the amphibian. This is sufficiently illustrated by the role played by 

 ammonia and ammonia compounds in the production of uric acid 

 in the birds and their congeners, f In the mammal, the taking of 

 food rich in nucleated cells) and therefore in nucleo-proteins and 

 nucleins, the characteristic conjugated proteins of nuclei (thymus 

 gland, pig's pancreas, and herring roe), (or of food rich in purin 

 bases (Liebig's meat extract), increases the quantity of uric acid in 

 the urine.^ The increase is mainly due to the production of uric 

 acid from the nuclein substances of the food. But this is not the 

 only source of the uric acid, sincef extracts of the thymus gland) 

 containing only traces of nucleins or nucleic acid cause,(when in- 

 jected, a characteristic increase in the uric acid excretion) just as 

 the entire gland does when taken by the mouth. And during the 

 period of increased nitrogen excretion occasioned by a meal contain- 

 ing protein, the increase in the uric acid occurs particularly in the 

 hours immediately following the ingestion of the food, and does not 

 last so long as the increase in the urea. Now, the nucleins of the 

 food are comparatively little affected during the earlier stages of 

 digestion (Hopkins and Hope). Whether in mammals any portion 

 of the uric acid comes from amino-acids is still in doubt, but there 

 are facts which indicate that a fraction of it may do so. We may 

 conclude, therefore, that in the mammal, as well as in the bird, a 

 portion of the uric acid, although certainly a far smaller portion in 

 the mammal, is derived from bodies other than the nuclein substances 

 of the food that is to say, from the nuclein substances of the tissues 

 contained particularly in the cell-nuclei and probably from the 

 ordinary proteins of both food and tissues. The portion derived 



