192 BACTERIOLOGY. 



duct of growth of certain bacteria has since furnished a 

 topic for coDsiderable discussion. 



Indol, the name by which this body is now generally 

 known, when acted upon by reducing agents, is seen to 

 become of a more or less conspicuous rose color. This 

 body was recognized as one of the products of growth 

 of the spirillum 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 character- 

 istic 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 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 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 appears, 

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

 They contain no iudol. 



