138 INFECTIONS OF THE DIGESTIVE TRACT 



one obtains after the lapse of fifteen minutes only a 

 browning of the isatin-sulphuric-acid solution with no 

 definite appearance of a green tint. This appearance is 

 probably to be interpreted as dependent on a mere trace 

 of methyl mercaptan. 



The method used for the determination of indol 

 obtained from distillation of putrefactive mixtures is 

 that based on the formation of a color compound due to 

 the combination of two molecules of indol with one 

 molecule of /3-napthaquinone-sodium-monosulphonate. 

 This method has proved in a high degree serviceable 

 and may be recommended on account of its accuracy 

 and quickness. The main features of this method 

 are as follows: 



The method is dependent upon the almost quantitative 

 precipitation of indol in alkaline solution by a dilute 

 solution of /3-naphthaquinone-sodium-monosulphonate. 

 A dilute solution of indol (1 : 500,000 parts of water) 

 made slightly alkaline with potassium hydroxide, gives 

 with one drop of a two per cent, solution of /3-naph- 

 thaquinone-sodium-monosulphonate a blue or green-blue 

 color. A more concentrated solution of indol will give 

 a precipitate which upon examination will be found to 

 consist of well-defined acicular needles, bluish in color 

 and closely felted together. The compound, evident 

 either as precipitate or as coloration, is completely 

 soluble in chloroform, with the production of a red color. 

 From this extract the indol may be determined quantita- 

 tively either by evaporating the chloroform or by match- 

 ing the color to a standard in the Duboscq colorimeter. 



