204 BACTERIOLOGY 



reactions, is a routine step in the identification of different 

 species of bacteria. Among these bodies is one that is pro- 

 duced by a number of organisms, and whose presence may 

 easily be detected by its characteristic behavior when 

 treated with certain substances. I refer to nitroso-indol, 

 the reactions of which were described by Beyer in 1869, 

 and the presence of which as a product of the growth of 

 certain bacteria has since furnished a topic for considerable 

 discussion. 



Indol, the name by which this body is generally known, 

 when acted upon by reducing-agents becomes of a more 

 or less decided 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 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 compounds 

 that give to feces 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 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 containing 



