INDOL PRODUCTION. 227 



By some workers the oxygen is removed from the 

 culture-medium by the use of the air-pump. 



Many other methods are employed for this special 

 purpose, but for the beginner those given will suffice. 



From what has been said, it may be inferred that tlie 

 cultivation of anaerobic bacteria is a simple matter 

 attended with but little difficulty. Such an opinion 

 will, however, be quickly abandoned when the beginner 

 attempts this part of his work for the first time, and 

 particularly when his efforts are directed toward the 

 separation of these forms from other organisms with 

 which they are associated. The presence of spore- 

 forming, facultative anaerobes in mixed cultures is 

 always to be suspected, and it is this group that renders 

 the task so difficult. At best the work requires undi- 

 vided attention and no small, degree of skill in bacterio- 

 logical technique. 



INDOL PRODUCTION. The generation of products 

 other than those that give rise to alterations in the reac- 

 tion of the media, and whose presence may be detected 

 by chemical reactions, is now a recognized step in the 

 identification of different species of bacteria. Among 

 these products is one that is produced by a number 

 of organisms, and whose presence may easily be de- 

 tected by its characteristic behavior when treated with 

 certain substances. I refer to nitroso-indol, the reac- 

 tions 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 consid- 

 erable discussion. 



Indol, the name by which this body is now generally 

 known, when acted upon by reducing-agents becomes 

 of a more or less decided rose color. This body was 



