228 B A CTERIOLOG Y. 



recognized as one of the products of growth of the 

 spirillum of Asiatic cholera first by Poel, and a short 

 time subsequently by Bujvvid and by Dunham, and for 

 a time was believed to be peculiarly characteristic 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. It is constantly present in putrefying 

 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 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 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 



