58 BACTERIOLOGY FOR NURSES 



Anaerobic Methods. Special methods have been devised for 

 the cultivation of anaerobic organisms, the principle of each being 

 the removal of free oxygen from the container in which the bac- 

 teria are growing. The earliest methods depended on the removal 

 of oxygen by mechanical means; later, other methods were em- 

 ployed whereby the oxygen might be displaced by an inert gas 

 such as hydrogen or absorbed by an alkaline solution of pyrogallol. 



Mechanical Exclusion of Air. Tubes of glucose agar or glu- 

 cose gelatin are heated and then rapidly placed in ice water to pre- 

 vent reabsorption of oxygen while the medium is hardening. The 

 tubes are inoculated by deep stabs after which the surface may be 

 covered with a layer of albolene; or tight-fitting corks covered 

 with sealing wax or paraffin may be used to replace the cotton 

 plugs. 



Displacement of Air by Hydrogen. This method consists in 

 passing a stream of hydrogen through an airtight chamber in which 

 the tubes or plates of inoculated media have been placed. Hydro- 

 gen may be generated from a mixture of zinc and sulphuric acid 

 in a Kipp's generator which is connected with a Novy jar contain- 

 ing the cultures. Hydrogen is allowed to flow through the jar 

 about ten minutes and the stopcocks are then closed. 



Chemical Absorption of Oxygen. Any vessel with a tight 

 cover such as a Novy jar or a Mason fruit jar may be employed. 

 Dry pyrogallic acid is placed in the bottom of the jar and a small 

 quantity of 5 per cent sodium hydroxide is poured over it. The 

 inoculated tubes are put in place and the jar immediately closed. 

 If plated cultures are being cultivated the plates must be raised 

 above the pyrogallic mixture. The method may be applied to 

 individual tubes ; the inoculated tube is placed in a larger one in 

 the bottom of which pyrogallic acid and sodium hydroxide solu- 

 tion have been placed. The larger tube is closed with a tight-fitting 

 rubber stopper. Still another method is to place the pyrogallic 

 mixture in a tumbler and invert the inoculated tube of solid medium 

 into it. A layer of oil is then run over the surface of the pyrogallic 

 acid to prevent the access of atmospheric oxygen. As the acid 

 absorbs oxygen it becomes first pale yellow, finally deepening to 



