CHEMICAL BASIS OF THE ANIMAL BODY. 1273 



boiling aqueous solutions, so that in concentrating fluids, such 

 as urine, in which its presence is conjectured, they should be 

 first rendered alkaline with sodium carbonate, thus forming a 

 non-volatile salt. Benzoic acid may be additionally recognized 

 by the following test: when treated with a little boiling nitric 

 acid and evaporated to dryness, the residue thus obtained yields, 

 on further heating, an unmistakable odour of nitrobenzene. 



When introduced into the body benzoic acid is readily and 

 largely converted into hippuric acid, while at the same time 

 small quantities of succinic acid may make their appearance. 

 The chief interest in the acid centres in the above relationship 

 to hippuric acid, a fact discovered by Wohler in 1824 and 

 specially interesting as being the first known instance of a 

 well-defined synthesis effected by the animal body, and the 

 starting-point for the disproval of Liebig's views as to the 

 fundamental difference in the metabolic processes of animal 

 and plant tissues. 



2. Hippuric acid. C 7 H 6 O 9 . [C 6 H 5 . C O . NH . CH 2 . 

 COOH.] (Benzoyl-glycine.) 



This acid is found in considerable quantities (1-5 2-5 p.c.) 

 in the urine of herbivora, and also, though to a much smaller 



FIG. 225. HIPPURIC ACID CRYSTALS. (After Funkc.) 



amount (0-1 1-0 grm. per diem) in the urine of man. It is 

 undoubtedly formed in the body by the union, with dehydra- 

 tion, of benzoic acid and glycine (see 339). 



It may be readily obtained from the urine of horses or cows, 

 more particularly when they are out to grass. The perfectly 

 fresh 1 urine is boiled with milk of lime in slight excess, by 



1 To avoid fermentative decomposition into benzoic acid and glycine. 



