CH. 3 XXXVII. ] CREATININE 563 



herbivora containing substances belonging to the aromatic group 

 the benzoic acid series. If benzoic acid is given to a man, it unites 

 with glycine with the elimination of a molecule of water, and is 

 excreted as hippuric acid 



CH 2 .NH 2 CH 2 NH.CO.C 6 H 5 



C 6 H,.COOH + | + H,0 



COQH COOH 



[Benzoic acid.] [Glycine.] [Hippuric acid.] [Water.] 



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

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

 plished by the living cells of the kid- 

 ney itself ; for if a mixture of glycine, 

 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 of the urine is 

 next to urea its most abundant nitro- 

 genous constituent. Some is derived 

 directly from the creatine of the meat FIG. 430. crystals of hippuric acid. 

 in the food. The remainder is a product 



of proteid katabolism, and the creatine of the muscles is possibly an 

 intermediate stage in its formation. This amount remains very 

 constant even when the proteid of the food is greatly reduced in 

 quantity. (Folin.) 



The formation of creatinine from creatine is represented in the 

 following equation : 



C 4 H 9 N 3 2 - H 2 = C 4 H 7 N 3 0. 



[Creatine.] [Water.] [Creatinine.] 



Creatine and creatinine are of considerable chemical interest, because 

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

 in the laboratory; the equation which represents the formation of 

 urea from creatine is as follows : 



C 4 H 9 N 3 O 9 + H,O = CON 2 H 4 + C 3 H 7 NO 2 . 



[Creatine.] ~ [Water.] [Urea.] [Sarcosine.] 



The second substance formed is sarcosine. Sarcosine is methyl- 

 glycine that is, amino-acetic acid in which one H is replaced by 

 methyl (GIL) 



/NH.CH 3 

 ltl2 \COOH. 



