4 68 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
/OH (p) /OH (p) 
C C H / =C 6 H 4 ( + C0 2 
x CH.,COOH X -CH 3 
(paraoxyphenylacetic (parakresol) 
acid) 
/OH (p) /OH 
2C H 4 < +30, = 2C i; H 4 ( + 2CO., + 2H,0 
X CH, X H 
(parakresol) (phenol) 
By a process of reduction, the oxy-acids probably yield the phenylpropionic 
and phenylacetic acids which have been found, thus : — 
OH (p) 
C Li H 4 / + 2H = C ( H y CH o .C00H + H,0 
X5H 2 .COOH 
(paraoxyphenylacetic (phenylacetic 
acid) acid) 
Aromatic bodies found in putrefaction not formed from tyrosine. — Indol, 
skatol, and skatolcarbonic acid are not formed by bacterial action on tyrosine, 
and their mode of formation is not very clearly known. According to 
Baumann, 1 they are not primary products of bacterial action on the proteid 
molecule, but are formed in the decomposition of an intermediate body, which 
is soluble in a mixture of alcohol and ether. E. and II. Salkowski '-' support 
this conclusion. Nothing further is known of this intermediate substance, 
except that it is not peptone. Neumeister 3 considers it possible that these 
substances may be synthetically built up by the bacteria from simpler aromatic 
compounds. Indol and skatol are formed from this mother substance in 
varying proportion, probably due to the action of different bacteria, but these 
have never been isolated. 
Indol, skatol, and skatolcarbonic acid belong to the indigo group of aromatic 
compounds. Indol on oxidation yields indoxyl, and on further oxidation, 
this yields indigo blue. By an inverse process of reduction from indigo blue, 
indol can be obtained. 4 To indol and skatol the faeces owe to a great extent 
their peculiar unpleasant odour. 
Indol, 5 C^HX x>CH, crystallises from water in small scales (M. P., 
X CH^ 
52° C, B. P., 245 D - 246° C). It is fairly soluble in hot, less so in cold water, 
and is easily soluble in alcohol, ether, chloroform, benzol, and petroleum ether. 
It distils over with steam ; this property may be used to separate it from 
other putrefaction products. 6 In long-continued putrefaction, indol gradually 
disappears ; according to Salkowski, this is due to evaporation. 
Indol may be recognised by the following tests : — 
1. A wooden match moistened with strong hydrochloric acid and then 
dipped into an alcoholic solution of indol turns a cherry-red colour. 
1 Ber. d. deutsch. chcm. Gcscllscli., Berlin, 1880, Bd. xiii. S. 2S4. 
2 Ztschr. f. physiol. Chcm., Strassburg, 1884, Bd. viii. S. 454 ; see also Nencki and Bovet, 
Monatsh.f. Chem., Wien, 1S89, Bd. x. S. 506. 
3 "Lehrbuch. d. physiol. Chem.,"' Jena, 1893, Th. 1, S. 209. 
4 Nencki, Ber. d. deutsch. chem. Gesellsch., Berlin, 1875, Bd. viii. S. 722 ; Baumann, 
u. Brieger, Ztschr. f. -physiol. Chcm., Strassburg, 1879, Bd. iii. S. 254. 
5 Baeyer, Ann. d. Chcm., Leipzig, Bd. cxl. S. 295 : Supp. Bd. vii. S. 56. 
6 For method of isolation from these, seeGamgee. " Physiological Chemistry, etc.," vol. ii. 
p. 421 ; or E. and H.' Salkowski, Ztschr. f. physiol. Chem., Strassburg, 1884, Bd. viii. S. 417. 
