CHANGES IN THE REACTION OF MEDIA 213 



an atmosphere from which all oxygen has been expelled. 

 As a reducing-agent for this purpose, Theobald Smith regards 

 a weaker solution of glucose, 0.3 to 0.5 per cent., as more 

 advantageous; and Wright obtains better results when 

 glucose is added if the primary reaction of the media is about 

 neutral to phenolphthalein. 



Method of Park. A very simple, convenient, and effi- 

 cient method is employed by Park. It consists in covering 

 the medium in which the anaerobic species are to be cul- 

 tivated with liquid paraffin (albolene). The best results 

 are obtained when the amount of paraffin added is about 

 half that of the liquid in the tube or flask. The liquid paraffin 

 has the advantage over the solid paraffin in not retracting 

 from the walls of the vessel on cooling. All air is expelled 

 from flasks or tubes prepared in this way, by heating them 

 in the autoclave. The layer of paraffin prevents the reab- 

 sorption of oxygen driven off by the heat. After cooling, the 

 inoculation is made by passing the needle through the paraffin 

 well down into the media. 



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 the cul- 

 tivation 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 bacteriological 

 technique. 



