INDOL PRODUCTION. 199 



matters, and is one of the aromatic bodies that give to 

 faeces their characteristic odor. 



The methods employed for its detection are as follows : 

 cultivate the organism for twenty-four to forty-eight 

 hours at a temperature of 37 C., in the simple pep- 

 tone 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 reaction when the amount of inclol 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 ap- 

 pears, or at least there is no production of a rose color. 

 They contain no indol. 



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

 the tubes which have 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 pro- 

 duced, the indol reaction may be considered as negative 

 i. e.j no indol has been formed as a product of the 

 growth of the bacteria. 



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 coincidently a reducing- 



