108 UREA. HIPPURIC ACID. AMINOACIDS 



may originate from one or other of two sources : First, from 

 aromatic products of vegetable food, as cinnamic acid, hy- 

 drocinnamic acid, quinic acid, etc., which in metabolism are 

 catabolized to benzoic acid. It is not remarkable, therefore. 

 that the quantity of benzoic acid, excreted in the form of 

 hippuric acid, may be decidedly increased by free ingestion 

 of vegetables and fruit (normally present in human urine in 

 amounts of 0.7 to 1. gram daily, on mixed diet) ; and that 

 herbivora eliminate a much larger quantity than carnivores. 

 A second important source is phenylalanin, one of the 

 molecular structural units of protein. Apparently this 

 compound (cf. Vol. I of this series, p. 47, et seq., Chemistry 

 of the Tissues) readily undergoes complete dissociation in 

 normal metabolism; however the phenylpropionic acid 

 which is produced in intestinal putrefactions from phenyl- 

 alanin (cf. Vol. I of this series, p. 32, Chemistry of the 

 Tissues) is oxidized freely into benzoic acid when it is 

 resorbed. 



PHENYLALANIN PHENYLPROPIONIC BENZOIC HIPPURIC ACID 



ACID ACID 



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



CH.NHj CH 2 COOH. 



COOH COOH 



The importance of protein putrefaction to the production 

 of hippuric acid and the fact that in dogs whose intestinal 

 canal has been largely disinfected by means of calomel the 

 hippuric acid may be materially lowered in the urine were 

 fully recognized by Baumann. 



The history of the second component part of hippuric 

 acid, glycocoll, is, however, incomparably more complicated 

 than that of the benzoic acid. Probably a clearer conception 

 of the processes here concerned can be had if herbivorous 

 and carnivorous animals are considered separately, as it is 

 becoming more and more evident, as Ernst Friedmann 28 has 



38 E. Friedmann and H. Tachau (First Med. Clinic, Berlin), Biochem. 

 Zeitschr., 55, 88, 1911. 



