METABOLISM 



Hippuric acid in small amounts is a normal constituent of the 

 urine of mammals but is especially abundant in that of herbivora. 

 Its formation is the result of a synthesis (204). When benzoic acid 

 or other compounds containing the benzoyl radicle are introduced 

 into the circulation they are paired with glycin, one of the cleavage 

 products of the proteins, in the kidneys and excreted as hippuric 

 acid, which, chemically, is benzoyl-glycin, or benzamidoacetic acid, 

 (C 6 H 5 CO)NHCH 2 COOH. The normal presence of small quan- 

 tities of hippuric acid in the urine arises from the fact that the putre- 

 faction of the proteins in the intestines yields compounds containing 

 the benzoyl radicle which are resorbed and combine with glycin to 

 form hippuric acid. But a small proportion of the hippuric acid pro- 

 duced by herbivora can be thus accounted for, however. Most of it 

 appears to owe its origin to the roughages consumed by these animals, 

 especially those derived from plants of the gramineae, while, on the 

 other hand, concentrates do not seem to increase its amount. Ap- 

 parently its formation bears some relation to some of the ingredients 

 of the cell walls, but to what ones in particular is not clear. 



229. The non-nitrogenous residue. In addition to the 

 nitrogenous products eliminated in the urine, the complete 

 oxidation of the protein molecule gives rise to the production 

 of considerable amounts of carbon dioxid and water, which are 

 excreted through the same channels as those derived from the 

 katabolism of carbohydrates or fats. To put the matter in the 

 reverse way, while the urinary products account for all the 

 nitrogen of the protein, they contain but a relatively small 

 part of its carbon, hydrogen and oxygen. This is clearly shown 

 by comparing the average amounts of these elements in 100 

 parts of protein with the quantities contained in the urea 

 corresponding to the total nitrogen of the protein. Disregard- 

 ing the sulphur of the proteins, the results of such a computation 

 are as follows : 



