i88 BIOLOGICAL CHEMISTRY 



Hippuric Acid is a compound formed by the union of 

 benzoic acid and glycine. 



COOH CONH'CH 2 COOH 



A 



NHCHCOOH = 



Benzoic Acid. Glycine. Hippuric acid. 



In the excretion of all the previous substances the function 

 of the kidney has been passive, in that it has merely excreted 

 the substances brought to it in the blood, but in the case of 

 hippuric acid the kidney causes its synthesis from benzoic 

 acid and glycine. A mixture of benzoic acid and glycine 

 perfused through the blood vessels of the kidney in the 

 presence of oxygen gives rise to the formation of hippuric 

 acid.* The synthesis occurs even with chopped up kidney 

 tissue. 



Hippuric acid is especially predominant in the urine of 

 herbivora, as they ingest a fair amount of benzoic acid. 

 The synthesis of hippuric acid depends on the amount of 

 benzoic acid supplied, glycine being always present in 

 sufficient amount. 



The interest of this synthesis is that it is a type of reaction 

 which is employed to render toxic substances non- toxic. 

 Salicylic acid and similar substances are combined with 

 glycine : camphor and other substances are combined with 

 glycuronic acid to form glycuronates. The union of phenolic 

 substances with sulphuric acid to form ethereal sulphate 

 has been already described. 



K ynurenic acid is found in the urine of dogs. Its formula is 



C-OHf 



COOH 



Allantoine is the form in which the purine derivates appear 

 in the urine of animals which can decompose uric acid. 



Sulphur Compounds. Sulphur is found in the urine in three 

 forms. The inorganic sulphates and ethereal sulphates have 

 been described under sulphur metabolism. The third form, 



* G. Bunge and O. Schmiedeberg, Arch. /. exper. Path. u. Pharm., 

 1877, vol. 6, p. 233. 

 f A. Homer, Journ. BioL Chem., 1914, vol. 17, p. 509. 



