200 BAOTJEBIOLOOY. 



By some workers the oxygen is removed from the 

 culture medium by the use of the air-pump. 



Mauy other methods exist for this special purpose, 

 but for the beginner those given will suffice. 



From what has been said it may be inferred that the 

 cultivation of anaerobic bacteria is a simple matter and 

 attended with but little difficulty. Such an inference 

 will, however, be quickly dispelled 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 bacteri- 

 ological technique. 



Indol PRODUCTioisr. — The production 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 chemical products there is one that is produced by 

 a number of organisms, and whose presence may easily 

 be detected by its characteristic behavior when treated 

 with certain substances. I refer to the body nitrosg-indol, 

 the reactions of which were described by Beyer in 1869, 

 and the presence of which as a product of the growtli 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, is seen to 

 become of a more or less conspicuous rose color. This 



