508 A MANUAL OF PHYSIOLOGY 



and butter. It is stated that the endogenous uric acid remains 

 practically constant in the same individual under constant con- 

 ditions, and is unaffected by changes in the diet. 



The total excretion of uric acid (and the other purin bodies) is 

 by no means identical with the sum of the uric acid taken in as 

 purin bases in the food and that produced in the body. A con- 

 siderable destruction of uric acid (and other purin bodies) goes 

 on in the body, and mainly in the liver. A ferment called the 

 uricolytic ferment has been discovered in various organs, and it is 

 believed that this is the active agent in the normal destruction 

 of uric acid. There is reason to think that one of the factors in 

 the production of gout may be a diminution in the amount or 

 activity of this ferment. In some cases it is said to be entirely 

 absent. The quantity of endogenous uric acid excreted by the 

 kidneys bears a certain ratio to the total amount which has 

 entered the circulation. This ratio varies much in different 

 mammalian species. In man a full half is excreted and about a 

 half destroyed. Some of the exogenous moiety is also broken 

 down. When uric acid is heated in a sealed tube with strong 

 hydrochloric acid, it is broken up into glycin, carbon dioxide, and 

 ammonia. There are grounds for believing that a similar decom- 

 position takes place in the body, and that the products are then 

 synthesized to urea in the liver. 



Hippuric acid can undoubtedly be produced in the kidney. 



If an excised kidney is perfused with blood containing benzoic 

 acid, or, better, benzoic acid and glycin, hippuric acid is formed. 

 The kidney cells must be intact, for if a mixture of blood, glycin, 

 and benzoic acid be added to a minced kidney immediately after 

 its removal from the body/ hippuric acid is produced, but not if 

 the kidney has been crushed in a mortar. Nevertheless there is 

 some evidence that a ferment is concerned in the reaction. In 

 herbivora hippuric acid cannot normally be detected in the blood ; 

 it is present in large quantities in the urine ; it must therefore be 

 manufactured in the kidney, not merely separated by it. In 

 certain animals, as the dog, the kidney is the sole seat of the 

 production of hippuric acid. But in the rabbit and the frog 

 some of it may also be formed in other tissues, for after extirpa- 

 tion of the kidneys the administration of benzoic acid causes 

 hippuric acid to appear in the blood. The benzoic acid comes 

 mainly from substances of the aromatic group contained in 

 vegetable food, but a small amount is produced in the body, 

 since hippuric acid does not entirely disappear from the urine 

 in starvation. It is not known in what form the nitrogenous 

 glycin appears on the spot where it is wanted to form hippuric 

 acid, since glycin has not been found anywhere in the tissues. 

 But there is no doubt that it is a product of the metabolism of 



