140 INFECTIONS OF THE DIGESTIVE TRACT 



been described, it is possible to remove almost completely 

 the indol from a solution containing both indol and skatol 

 and that the skatol remaining after the removal of 

 the indol can be distilled and recognized by means of 

 the dimethylamidobenzaldehyde reaction described by 

 Ehrlich. If one takes a putrefactive mixture containing 

 both indol and skatol, these bases should first be dis- 

 tilled either in acid or alkaline solution preferably 

 with the aid of steam if the quantities are considerable. 

 In the distillate the skatol passes over earlier than the 

 indol, as can easily be shown by means of the blue color 

 which it gives on boiling with Ehrlich's aldehyde. To 

 the distillate containing the indol enough sodium 

 or potassium hydroxide is added to render it slightly 

 alkaline. An excess of the /3-naphthaquinone-sodium- 

 monosulphonate is now added to this solution. As 

 already described, this substance in the course of a few 

 minutes reacts almost completely with the indol present, 

 but not with the skatol. The blue or purplish-blue 

 precipitate of the newly formed indol-naphthaquinone 

 compound is now removed by filtration. In cases where 

 the concentration of indol is too small to give rise to 

 a precipitate when treated with the naphthaquinone 

 compound the solution simply develops a green or 

 greenish-blue color. The solution is now acidified and 

 subjected to distillation, with or without the use of steam. 

 The skatol passes over into the distillate, whereas the in- 

 dol is held back in the form of the indol-naphthaquinone 

 compound, with the exception of a very small uncom- 

 bined portion, which passes over with the skatol. The 



