76 APPLIED EACTEEIOLOGY 



All the ordinary culture media contain traces of free 

 oxygen, and will absorb more on standing. For the 

 growth of anaerobes, this oxygen may be got rid of by 

 one of the following methods : (a) By growth in a vacuum ; 

 (&) by growth in an atmosphere of an inert gas, such as 

 hydrogen or carbon dioxide ; (c) by additions of a reducing 

 substance to the media which does not interfere with the 

 bacterial growth. Such additions take up any free oxygen 

 there may be in the medium, and prevent further absorp- 

 tion. The chief substance used for this purpose is glucose 

 (grape-sugar), which, when added to the extent of 2 per 

 cent, to nutrient gelatine or agar, gives very good results in 

 the case of the bacillus of tetanus. Small additions of 

 resorcine, formate of soda, and sulphindigotate of sodium 

 have also been employed as additions to culture media for 

 the purpose of extracting oxygen. 



The most simple method is to place the tubes or plates 

 under the receiver of an air-pump, and then withdraw the 

 air. 



Griiber's method of effecting the removal of oxygen is as 

 follows : The culture material is inoculated into a culture- 

 tube by means of Esmarch's method. The cotton-wool plug 

 is then pushed down the tube to about an inch in depth ; and 

 above is inserted an indiarubber stopper, which must be well- 

 fitting, and which is pierced with a hole, through which 

 passes a glass tube. The air is then exhausted from the 

 tube by connecting the tube to an air-pump. When this is 

 done, the glass tube is sealed by means of a blowpipe flame. 



The eggs of birds can also be successfully used for the 

 culture of rnany anaerobic organisms by the method which 

 has been already described. 



The most generally used and satisfactory method for the 

 cultivation of the anaerobic bacteria is the following modifi- 

 cation of the Esmarch roll-tube : 



