72 



A MANUAL OF BACTERIOLOGY 



it will be found that the most strictly anaerobic organisms 

 can be cultivated in this way. 



When, however, an organism is required to grow 

 anaerobically on the surface of the medium, or in a fluid 

 medium, some other method must be -adopted. The tubes 

 may be placed under the receiver of 

 an air-pump and exhausted as com- 

 pletely as possible. This is not very 

 convenient, for it is difficult without great 

 care to maintain a vacuum, and special 

 receivers must be used when the cultures 

 have to be kept in the incubator, while 

 with fluid media ebullition may cause 

 considerable difficulty. 



For fluid cultures Hamilton's method 

 is the simplest of all. The fluid in the 

 tubes is covered with a layer of olive oil 

 1-2 cm. thick, and the tubes are then 

 sterilised. The layer of oil prevents the 

 access and entrance of oxygen. The only 

 disadvantage is that the inoculation, or 

 the withdrawal of culture, must usually 

 be performed with a sterile glass pipette ; 

 FIG. 11. Buchner's ^ a w i re needle be used the material is 

 tube arranged for very liable to be detached in the oil. 

 vat^n.^ Another method (Buchner's) is that 



usually adopted, and consists in absorb- 

 ing the oxygen by means of alkali and pyrogallic 

 acid, and so cultivating in an atmosphere of nitrogen. 

 This can be carried out in two ways either in a wide- 

 mouthed bottle with well-fitting glass stopper, sufficiently 

 large to contain the test-tubes, or in a Buchner's tube. 

 For the first the inoculated culture tubes are placed 

 in the bottle, into which a few cubic centimetres of a 

 strong aqueous solution of pyrogallic acid have previously 



