HIPPURTC ACID 107 



in an autoclave (Benedict and Gephart, 24 and Henriques 

 and Gammeltoft 25 ), or very conveniently by heating with 

 glacial phosphoric acid in open vessels (Braunstein), or 

 finally by heating with potassium acetate and addition of 

 acetic acid and zinc (Folin). 26 Naturally there are any num- 

 ber of variations and combinations of these methods pos- 

 sible. In spite of this apparent richness it must be confessed 

 that all of these methods are indirect ; and that in case other 

 related substances occur in addition to urea, with their 

 nitrogen similarly combined in the structural molecule, it 

 would be difficult to detect them against the urea, to say noth- 

 ing of estimating them. 



Attempts to determine urea quantitatively by splitting it 

 into carbonic acid and nitrogen by means of nitric acid, with 

 subsequent determination of nitrogen by Dumas' method 

 have been repeatedly proposed. 27 



HIPPURIC ACID 



After the preceding presentation of the knowledge we 

 at present possess of the formation of urea in the living 

 body, our attention naturally is directed to other nitrogenous 

 end-products of protein metabolism, of which hippuric acid 

 may first be dealt with. 



As is well known hippuric acid is a combination product 

 arising from the union of glycocoll and benzoic acid : 



CH 2 .NH 2 CH 2 .NH CO.C,H 8 



| + C 6 H 6 .COOH=H 2 O + I 



COOH COOH. 



Source of Benzoic Acid. As far as the benzoic acid com- 

 ponent is concerned our knowledge is fairly established. It 



24 S. R. Benedikt and F. Gephart, Journ. of the Amer. Chem. Soc., SO, 

 1760, 1908; P. A. Levene and G. H. Meyer, ibid., 31, 717; G. L. Wolf and E. 

 Osterberg, ibid., 31, 421; F. W. Gill, F. G. Allison and H. S. Grindley, ibid., 31, 

 1078 ; abstract in Centralbl. f . Physiol., 23, 1909. 



25 V. Henriques and S'. A. Gammeltoft ( Copenhagen ) , Skandin. Arch., 25, 

 153, 1911. 



26 O. Folin (Harvard Medical School), Jour, of Biol. Chem., 11, 507, 1912. 

 "Th. Ekekrantz, with K. A. Sodermann and S. Erikson (Stockholm), 

 Zeitschr. f. physiol. Chem., 76, 173, 1912; 79, 171, 1912. 



