INDOL PRODUCTION. lg\ 



istic of the growth of this organism. It has since been 

 found that there exist other bacteria which also possess 

 the property of producing indol in the course of their 

 development. 



The method employed for its detection is as follows : 

 Cultivate the organism for twenty-four to forty-eight 

 hours at a temperature of 37° C, in the simple peptone 

 solution known as " Dunham's solution " (see formula 

 for this medium). This solution is preferred because 

 its pale color does not mask the rose color of the reac- 

 tion when the amount of indol present is very small. 



Four tubes should always be inoculated and kept 

 under exactly the same conditions for the same length 

 of time. 



At the end of twenty-four or forty-eight hours the 

 test may be made. Proceed as follows : To a tube con- 

 taining 7 c.c. of the peptone solution, but which has not 

 been inoculated, add 10 drops of concentrated sulphuric 

 acid. To another similar tube add 1 c.c. of a 0.01 per 

 cent, solution of sodium nitrite, and afterward 10 drops 

 of concentrated sulphuric acid. Observe the tubes for 

 five to ten minutes. No alteration in their color appears, 

 or at least there will be no production of a rose color. 

 They contain no indol. 



Treat in the same way, with the acid alone, two of 

 the tubes which Jiave been inoculated. If no rose color 

 appears after five or ten minutes, add 1 c.c. of the sodium 

 nitrite solution. If now no rose color is produced, the 

 indol reaction may be considered as negative. No indol 

 is present. 



If indol is present, and the rose color appears after 

 the addition of the acid alone, it is plain that not only 

 indol has been formed, but likewise a reducing body. 



