INDOL PRODUCTION. 201 



body was recognized as one of the products of growth 

 of the spirilhim of Asiatic cholera first by Poel, and a 

 short time subsequently by Bujwid and by Dunham, 

 and for a time was thought to be peculiarly charac- 

 teristic of the growth of this organism. It has since 

 been found that there are many 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 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 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 ap- 

 pears, or at least there will be no production of a rose 

 color. They contain no indol. 



Treat ia 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- 



