CH. xxxvii.] CREATININE. 559 



animal body, and experimental investigation shows that it is 



accomplished by the living cells 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 Rg 434 ._cry 8 teis of hippuric acid. 

 small amount in the urine even 



during starvation : this possibly represents a small percentage 

 of creatine from the muscles. 



The formation of creatinine from creatine is represented in the 

 following equation : 



C 4 H 9 N 8 2 - H 2 = C 4 H 7 N 3 O 



[Creatine] [Water] 1 [Creatinine]. 



Creatine and creatinine are of considerable chemical interest, 

 because urea can be obtained from them as one of their decom- 

 position products in the laboratory ; the equation which represents 

 the formation of urea from creatine is as follows : 



C 4 H 9 N 8 2 + H 2 = CON 2 H 4 + C 3 H 7 N0 2 



[Creatine] [Water] [Urea] [Sarcosme]. 



The second substance formed is sarcosine. Sarcosine is methyl- 

 glycocine that is, amido-acetic acid in which one H is replaced 

 by methyl (CH 8 ) 



NH.CH 8 

 2 ^ 



It is, however, doubtful whether decompositions of this kind 

 occur in the body. 



Creatinine with zinc chloride gives a characteristic crystalline 

 precipitate (groups of fine needles) with composition 



C 4 H 7 N 8 O.ZnCl 2 . 



According to the recent researches of G. S. Johnson, urinary 

 creatinine, though isomeric with the creatinine obtained arti- 

 ficially from the creatine of flesh, differs from it in some of 



