64 PURE CULTURE OF BACTERIA 



clear, the organism is anaerobic ; facultative anaerobes usually 

 render the whole contents of the tube turbid. 



Inoculate a specimen of both the above tubes of media with 

 Bact. coli and note the results. 



Ex. 37. Melt a few tubes of nutrient beef broth gelatine con 

 taining glucose (see Ex. 25), and inoculate them with various 

 organisms to be tested for gas production. 



Allow them to cool and solidify, then incubate at 20 C. ; if 

 gas is produced it collects in bubbles throughout the medium. 



Try a tube with Bact. coli. and note the results. 



Cultivation of Anaerobic Bacteria. In the cultiva- 

 tion of anaerobes it is necessary to devise some means 

 for excluding the oxygen from, or for removing it from, 

 the space surrounding the medium. 



The air may be expelled from the medium by boiling ; 

 it may be extracted with the air-pump, or it may be 

 displaced by hydrogen, nitrogen, or some other gas. 



The simplest arrangements for the growth of anaerobes 

 are the following : 



(1) Cultivation in a deep stab in agar or gelatine. 



(2) Cultivation in a Buchner's tube. 



Ex. 38. (i) Anaerobic Cultivation in a Deep Stab. Take a 

 tube which is more than half full of agar or gelatine medium 

 and place it in a beaker of warm water; heat to boiling for five 

 minutes so as to expel the dissolved air from the medium. 



Cool the tube in water, and when the agar or gelatine is 

 solidified, make a deep stab to near the bottom of the tube with 

 a long platinum needle, upon which are the organisms to be 

 grown ; rotate the needle and then withdraw it. In the recently 

 melted medium the track of the needle closes up. 



Now gently melt the upper layer of the medium by rotating it 

 rapidly near a Bunsen flame ; this more effectually closes the 

 track, 



