198 INDOL. 



substance does not. No simple directions can be given for the 

 separation and estimation of pyrocatechin in presence of phenol, 

 kresol and hydrochinon 1 . 



But little is known as to the source of this substance in urine apart 

 from its probable formation from the phenol produced by putrefactive 

 changes in the alimentary canal. In herbivora there is some evidence 

 that it is derived from certain aromatic constituents of their food 2 . 



8. Hydrochinon. C 6 H 4 (OH) 2 . Paradioxy benzol. 



Has not yet been described as occurring normally in urine, but only 

 as the result of the ingestion of phenol. It exists in urine as an 

 ethereal compound with sulphuric acid and is largely the cause of 

 the dark colour which this excretion assumes after the absorption of 

 phenol on exposure to the air. It resembles pyrocatechin in effecting 

 the reduction of metallic salts, but differs from it in being nearly 

 insoluble in cold benzol and in not yielding any precipitate with 

 normal lead acetate. This latter property suffices for its separation 

 from pyrocatechin. It is readily converted by oxidation into chinon 

 C 6 H 4 2 whose characteristic odour affords a further means of identifi- 

 cation, and when heated in an open test-tube it yields a blue 

 sublimate 3 . 



The third known isomeric dioxybenzol viz. meta-dioxybenzol or 

 resorcin has not yet been found in the animal body or in urine. 



THE INDIGO SERIES. 

 Indol. C 8 H 7 N. 



Indol occurs characteristically in the faeces, to which with skatol it 

 imparts their peculiarly unpleasant odour 4 . Its presence here is due 

 to its formation during the putrefactive decomposition of proteids which 

 usually occurs to a greater or less extent in the alimentary canal, part 

 of the indol leaving the body in the urine as a potassium salt of indoxyl- 

 sulphuric acid (see below), the remainder being excreted with the faeces. 

 It may readily be obtained, contaminated by varying quantities of phenol 



1 See Baumann, Zt.f. physiol. Chem. Bd. vi. (1882), S. 183. Schmiedeberg, loc. 

 cit. S. 304. 



2 Preusse, Zt. f. physiol. Chem. Bd. n. (1878), Sn. 324, 329. 



3 In addition to the literature precedingly quoted see more particularly 

 Baumann u. Preusse, Arch. f. Physiol. Jahrg. 1879, S. 245. Brieger, Ibid. Suppe- 

 Hft. S. 66. Baumann u. Preusse, Zt. f. physiol Chem. Bd. vn. (1889), S. 156. 

 Baumann, Ibid. Bd. vi. (1882), S. 188. 



4 Kadziejewski, Arch. f. Anat. u. Physiol. 1870, S. 42. 



