CHANGES IN THE REACTION OF MEDIA 221 



Sterilize and inoculate with Bacillus coli communis. How 

 do the two tubes differ from one another after eighteen 

 to twenty-four hours in the incubator? First, as regards 

 the reaction of the fluid in the open arms of the tubes. 

 Second, as to accumulation of gas in closed arms of the 

 tubes. Third, as to the capacity of each solution for 

 reducing copper in Fehling's solution. What differences 

 are observed, and how may they be explained? 



Indol Production. The detection of products other than 

 those that give rise to alterations in the reaction of the 

 media, and whose presence may be demonstrated by chemical 

 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. 



