ACTION OF INTESTINAL BACTERIA ON PROTEIDS. 469 



2. An aqueous solution of indol treated with fuming nitric acid turns a 

 bright red colour, and on standing a red precipitate is formed. 



3. When sodium nitroprusside is added to a very dilute solution of indol, 

 and afterwards caustic soda, the mixture turns a deep violet-blue, passing into 

 a pure blue on making faintly acid with acetic acid, and disappearing with 

 excess of acid (Legal's reaction). 1 



/xn. 



Skatol, 2 C 6 Hy />CH, is methyl-indol ; it crystallises in similar form 



to indol (M. P., 95 C., B. P., 265 - 266 C.). It also possesses much the 

 same solubilities as indol, and is volatile with steam. Passed through a red- 

 hot tube, it decomposes and yields indol. 



It is distinguished, in addition to its physical properties, by the following 

 tests : 



1. Instead of a red precipitate, as in the case of indol, it gives a milky 

 turbidity when treated with fuming nitric acid. 



2. In Legal's test (vide supra) it gives an intense yellow, turning violet 

 with acid. 



3. It dissolves in concentrated hydrochloric acid, giving a highly coloured 

 solution. 



Both indol and skatol, dissolved in benzol in concentrated solution, give, 

 with a saturated solution of picric acid in benzol, a crop of fine red crystals. 

 When the compound of indol and picric acid is treated with caustic soda, and 

 distilled, the indol is decomposed ; under similar conditions the skatol picric 

 acid compound yields skatol which is not decomposed. 



/ NH \ 



Skatol carbonic acid, 3 C fl H 4 <^ /C'COOH, crystallises in scales (M. P., 



NT 1 PIT S/ 



N U.UH 3 ' 



164 C.), sparingly soluble in water, easily soluble in alcohol and ether. Heated 

 above its melting point, it breaks up into skatol and carbon-dioxide. 

 It may be identified by the following tests : 



1. Its aqueous solution, treated with pure nitric acid and afterwards with 

 potassium nitrite solution, turns a cherry -red colour, and deposits a red pre- 

 cipitate, which is dissolved by acetic ether. 



2. Its aqueous solution, treated with an equal volume of hydrochloric acid 

 (sp. gr. 1'2), and afterwards with dilute bleaching powder solution, gradually 

 turns a purple-red colour, and, after long standing, deposits a purple-red 

 precipitate, easily soluble in alcohol. 



3. A very dilute solution (1 in 10,000 of water), treated with a few drops 

 of hydrochloric acid, then with a few drops of a very dilute solution of ferric 

 chloride, and heated, gives an intense violet colour. More concentrated solution 

 gives an intense cherry-red colour. 



The aromatic compounds resulting from bacterial decomposition in the 

 intestine are to a considerable extent absorbed. Tyrosine absorbed as such 

 disappears ; it is decomposed and completely oxidised in the tissues without 

 the formation of urea. The non-nitrogenous substances resulting from its de- 

 composition by bacteria (as well as indol and skatol) are not completely 

 oxidised, but are excreted in modified form in the urine, combined chiefly 

 with sulphuric acid, as ethereal sulphates, but also in part with glycocoll and 

 glycuronic acid. In this way the poisonous properties of the phenols and 

 similar compounds are removed, for the ethereal sulphates formed are very 



1 Breslau. arztl. Ztschr., 1893. 



2 Brieger, Ber. d. deutseh. chem. Gesellsch., Berlin, 1877, Bd. x. S. 1028. 



3 E. and H. Salkowski, Ztschr. f. physiol. Chem., Strassburg, 1885, Bd. ix. S. 8. 



