104 CHEMISTRY OF THE PROTEIDS CHAP. 



The other two aromatic groups behave similarly : phenylamino- 

 propionic acid -> phenyl-propionic acid ~ phenyl-acetic acid ; and 

 indolamino-propionic acid -> indol-propionic acid -> indol-acetic acid 

 -> skatol -> indol. 



Benzoic acid has not yet been found. 



Phenol, indol, and skatol are looked upon as the characteristic 

 products of putrefaction, as they are readily recognised by their smell, 

 and because they are absorbed as the final products of intestinal 

 putrefaction and then excreted in the urine as paired sulphonic acids. 1 

 But these substances are by no means formed by all bacteria. Phenyl- 

 acetic acid or a-toluylic acid is eliminated as phenaceturic acid. 2 



CH 2 COOH becomes <^)> CH 2 . CO . NH . CH 2 . COOH. 



Phenyl-acetic acid. Phenaceturic acid. 



The fatty series is represented by formic acid and carbonic acid, 

 both of which are constantly present. They may be formed by a 

 method analogous to that described above for the aromatic series, but 

 whether the same holds good for the other aliphatic acids cannot as 

 yet be considered as settled, for they may be derived either from 

 ammo-acids or from higher homologues. 



Cystin gives rise to sulphuretted hydrogen, which is another 

 characteristic product of putrefaction. Salkowski, Baumann, Rubner, 

 Morner, Nencki, and Zoja observed also methylmercaptane, but great 

 caution is necessary in explaining its derivation, because Rubner has 

 shown that it may be formed synthetically. 



2. Disintegration during the Metabolism of Plants, exclusive of Bacteria. 

 Most light has been thrown on this question through the work of 

 E. Schulze 3 and his pupils. There are contained in the seeds of 

 plants certain albuminous substances which serve as a storehouse for 

 the growing embryo, and these are made available through the action 

 of proteolytic enzymes, whenever germination commences. These 

 enzymes have been examined by v. Gorup-Besanez, 4 Neumeister, 5 

 Weis, 6 Butkewitsch, 7 and others ; they act analogously to trypsin, for 



1 E. Baumann and E. Herter, Ber. d. deutsch. chem. Ges. 1. 244 (1877). 



2 E. and H. Salkowski, ibid. 9. 491 (1885). 



3 E. Schulze, ibid. 24. 18 (1897), 26. 411 (1899), 30. 241 (1900), (in these 

 three papers is a summary of the previous ones) ; E. Schulze and E. Winterstein, ibid. 

 33. 547 (1901), 35. 299 (1902). 



4 v. Gorup-Besanez, Ber. d. deutsch. c/iem. Ges. 7. II. 1478 (1874) ; 8. II. 1510 

 (1875). 



5 R. Neumeister, Zeitschr.f. Biol. 30. 447 (1894). 

 G F. Weis, Zeitschr. f. physiol. Chem. 31. 79 (1900). 

 7 Wl. Butkewitsch, ibid. 32. 1 (1901). 



