CHEMICAL BASIS OF THE ANIMAL BODY. 189 



before but is now decomposed, yielding a sublimate of benzoic acid 

 accompanied by an odour like that of new hay, while oily red drops are 

 observed in the tube. When treated with boiling nitric acid (see above 

 sub benzoic acid) and evaporated to dryness the residue, on being heated 

 yields the marked and characteristic odour of nitrobenzol (Liicke's 

 reaction 1 ). As already stated hippuric acid owes its formation in the 

 body to a union of benzoic acid with glycin, so that its source must be 

 sought for in the modes by which benzoic acid (aromatic substance) is 

 introduced into or arises in the body. The source is probably of more 

 than one kind. Hay and grass were long since stated 2 to contain some 

 substance which yields hippuric acid in the body : this may be extracted 

 by means of dilute sulphuric acid, less readily by caustic potash 3 . More 

 recent researches have shown the presence in grass, hay, and many 

 fruits and berries not only of some benzoic acid but also of substances 

 such as quinic acid (OH) 4 C 6 H 7 . COOH, which readily yield benzoic 

 acid and are hence a source of hippuric acid 4 . A further source is 

 found in the aromatic (benzoic) products of the putrefaction of proteids, 

 such as in especial phenyl-propionic acid (C 6 H 5 . CH 2 . CH 2 . COOH) 5 

 which in its amidated form is more particularly a product of the decom- 

 position of vegetable proteids 6 , and yields benzoic acid by oxidation. 

 This substance has been found in the rumen of cows fed with hay 7 . 

 These facts coupled with the marked occurrence of putrefactive changes 

 in the alimentary canal of herbivora probably account for the prepon- 

 derance of hippuric acid in their urine. In carnivora it appears that 

 some traces of hippuric acid may be observed during starvation 

 originating here from the aromatic residues of the tissue proteids ; 

 also during an exclusively meat-diet 8 . When fed on a mixed diet 

 some of the hippuric acid arises from the benzoic and allied constituents 

 of the vegetable part of the food and probably not an inconsiderable 

 amount from the putrefactive products of the proteids in the alimen- 

 tary canal ; in accordance with this it is found that disinfection of the 

 alimentary canal in dogs with calomel diminishes the output of the 

 acid 9 . Tyrosin, notwithstanding its aromatic constitution, does not 

 give rise to hippuric acid when administered to man 10 . 



Arch. f. path. Anat. Bd. xix. (1860), S. 196. 

 Meissner u. Shepard, Die Hippursdure. 1866. 

 Weiske, Zt. f. Biol. Bd. xii. (1876), S. 241. 



For refs. see Salkowski u. Leube. Die Lehre vom Harn, 1882. S. 131. 

 E. u. H. Salkowski. Zt. f. physiol. Chem. Bd. vn. (1885), S. 161. 

 Schulze u. Barbieri, Ber. d. d. chem. Ges. 1883, S. 1711. Jn. f. prakt. Chem. 

 (N.F.) Bd. xxvn. (1883), S. 337. 



7 Tappeiner, Zt. f. Biol. Bd. xxn. (1886), S. 236. 



8 Salkowski, E., Ber. d. d. chem. Gesell. 1878, S. 500. Arch. f. path. Anat. Bd. 

 73, (1878), S. 421. 



9 Baumann, Zt. physiol. Chem. Bd. x. (1886), S. 123. 

 10 Baas, Ibid. Bd. xi. (1887), S. 485. 



