236 METHODS OF CULTIVATION 



ANAEROBIC CULTIVATIONS. 



Numerous methods have been devised for the culti- 

 vation of anaerobic bacteria, the majority requiring 

 the employment of special apparatus. The principle 

 upon which any method is based and upon which it 

 depends for its success falls under one or another of the 

 following headings: 



(a) Exclusion of air from the cultivation. 



(b) Exhaustion of air from the vessel containing the 

 cultivation by means of an air pump i. e., cultivation 

 in vacua. 



(c) Absorption of oxygen from the air in contact with 

 the cultivation by means of pyrogallic acid rendered alka- 

 line with caustic soda i. e., cultivation in an atmos- 

 phere of nitrogen. 



(d) Displacement of air by an indifferent gas, such 

 as hydrogen or coal gas i. e., cultivation in an atmos- 

 phere of hydrogen. 



(e) A combination of two or more of the above 

 methods. 



A selection of the simplest and most generally useful 

 methods is given here. 



Whenever possible, the nutrient media that are em- 

 ployed in any of the processes should contain some 

 easily oxidisable substance, such as sodium formate 

 (0.4 per cent.) or sodium sulphindigotate (o.i per 

 cent.), which will absorb all the available oxygen held 

 in solution by the medium. The further addition of 

 glucose, 2 per cent., favors the growth of anaerobic 

 bacteria (vide, pages 189-190). 



Further, it is advisable to seal all joints between 

 india-rubber stoppers and tubulures or the mouths 

 of the tubes with melted paraffin; glass stoppers and 

 taps should be lubricated with resin ointment or a 

 mixture of beeswax i part, olive oil 4 parts. 



