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CULTURES OF ANAEROBIC BACTERIA. 



Obligative anaerobic bacteria, those which grow only 

 in the absence of oxygen, require special conditions for cul- 

 tivation. Their growth is favored by the addition of 1 to 2 

 per cent, of glucose to the nutrient, medium, whether gel- 

 atin, bouillon or agar. Freshly prepared media are, as a 

 rule, best adapted for culture purposes. 



The numerous methods which have been proposed for 

 obtaining growths of anaerobic bacteria can be classified 

 under the following heads: 



(1.) Exclusion of oxygen. 



(2.) Exhaustion of air. 



(3.) Absorption of oxygen. 



(4.) Displacement of air. 



(5.) Cultures apparently in the presence of air. 



The well-known method of Liborius, of culture in 

 deep layers of gelatin or agar, depends upon the exclusion 

 of air. The method is .simple and very convenient. The 

 culture-tubes contains glucose agar or gelatin, l|-2 inches 

 high. Stich cultures are made in the usual manner. 

 Growth develops in the lower two-thirds of the medium, 

 while the upper layer of J to inch serves to exclude the 

 air. In order to insure complete exclusion of oxygen, the 

 contents of an ordinary agar orgelatin tube can be lique- 

 fied and then, with proper precautions against contamina- 

 tion, poured on top of the inoculated medium and quickly 

 cooled. This extra layer is, as a rule, unnecessary. 



Colonies of anaerobic bacteria can be obtained by 

 making ordinary gelatin or agar plates, and then placing* a 

 sterilized glass plate on top to exclude oxygen. 



Vacuum cultures are frequently resorted to. Gruber's 



