550 WASTE-PRODUCTS 



Thus Hopkins and Hope, after fasting for six hours, consumed a meal 

 of bread and potatoes, pratically purine-free, with the following results: 



Uric acid, 

 milligrams. 



26 

 27 

 24 

 21 

 22 

 38 

 40 

 56 

 39 

 30 

 33 

 24 

 23 



Thus a slight rise in the urea output occurred about six hours after 

 the ingestion of the food, and continued for some time, but a sharp 

 rise in the uric acid output occurred within two hours, and the excre- 

 tion fell tc nearly the normal value again before the urea excretion 

 began to rise. It is not known where this uric acid originates, but 

 it would appear to be manifestly connected with the activities of the 

 alimentary canal,. and to be endogenous in origin. It is for this reason 

 that the uric acid and purine output is greater during the day than 

 it is at night. 



In birds and .reptiles the relationships are quite different. These 

 possess the power of synthesizing uric acid, most probably from 

 Ammonia and Lactic Acid, since, if the liver be extirpated in birds, the 

 place of the uric acid in the excreta is taken by ammonia, and large 

 amounts of lactic acid are excreted concurrently. An increase of uric 

 acid elimination in birds follows the administration of lactic acid and 

 other hydroxy-acids and dibasic acids of the aliphatic series. This 

 power is, however, lacking in the mammalia. 



In the majority of mammals, uric acid is not the end-product of 

 the purine metabolism, but undergoes in part or almost wholly, trans- 

 formation into Allantoin which is excreted in the urine: 



HN co H 2 N 



oc 



+ H 2 + O = 



HN 



.This transformation, which is known as Uricolysis, is brought about by 

 an oxidizing enzyme, Uncase, which occurs in tissue-extracts prepared 

 from the liver, kidney and other organs. It trantforms uric acid almost 

 quantitatively into allantoin. It is probable, however, that the destruc- 

 tion of uric acid does not stop at this stage but proceeds further and, 

 ultimately, to the formation of urea and other products. Thus Ascoli 



