URINE 123 



and consequently increase in the metabolism of their nuclei ; some 

 investigators think, however, that the increase is chiefly due to 

 nuclein in the food. The question is 

 not yet settled. 



HIPPUEIC ACID 



Hippuric acid (C9H9NO3), com- 

 bined with bases to form hippurates, 

 is present in small quantities in 

 human urine, but in large quantities 

 in the urine of herbivora. This is 

 due to the food of herbivora con- 

 taining substances belonging to the 



aromatic group— the benzoic acid "~i:i^. 44.-Hipparic acid ciystaK 

 series. If benzoic acid is given to 



a man, it unites with glycocine with the elimination of a molecule 

 of water, and is excreted as hippuric acid — 



CHj.NHj CHaNH.CO.CeHs 



CfiHs.COOH-i- I = i +H2O 



COOH COOH 



[benzoic acid] [glycocine] [hippuric acid] [water] 



This is a weU-marked instance of synthesis carried out in the 

 animal body, and experimental investigation shows that it is ac- 

 complished by the hving c6lls of the kidney itself ; for if a mixture of 

 glycocine, benzoic acid, and blood is injected through the kidney (or 

 mixed with a minced kidney just removed from the body of an 

 animal), their place is found to have been taken by hippuric acid. 



CREATININE 



The creatinine in the urine is nearly all derived from the creatine 

 contained in the meat of the food. There is, however, a small 

 amount in the urine even during starvation : this represents a small 

 percentage of creatine from the muscles. 



Sarcosine (C3H7NO.2) united to cyanamide (CN.NHj) yields 

 creatine (C4H9N3O2). Cyanamide plus water yields urea (CON2H4). 



The formation of creatinine from creatine is represented in the 

 following equation : — 



C4H9N302-H20 = C4H7N30 



[creatine] [water] [creatinine] 



Creatine and creatinine are of considerable chemical interest, because 

 urea can be obtained from them as one of their decomposition products 



