CULTIVATION WITHOUT OXYGEN. 209 



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. 



14 



