INDOL PRODUCTION. 191 



In this method the colonies develop along the sides of 

 the tubes, and can more easily be studied than where 

 they are mixed through the gelatin, as in the method 

 of Liborius. 



By some workers the oxygen is removed by actual 

 pumping with the air-pump. 



Many 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 

 isolation 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 PKODUCTION. The production of products 

 other than those that give rise to alterations in the 

 reaction of the media, and whose presence may be de- 

 tected 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 nitroso-indol, the reactions of which were described 

 by Beyer in 1869, and the presence of which as a pro- 



