CULTIVATION WITHOUT OXYGEN. 



177 



a plug of cotton is placed ; this is to prevent access of 

 foreign organisms during manipulation. At the inner 

 side of the rubber stopper — that is, the end which is to 

 be inserted into the test-tube — the glass tubes are of 

 different lengths : one reaches to within 0.5 cm. of the 

 bottom of the test-tube, the other is cut off flush with 



Fig. 35. 



Frankers method for the cultivation of anaerobic bacteria. 



the under surface of the stopper. This rubber stopper, 

 with its glass tubes, is to replace the cotton plug of the 

 test-tube ; the outer end of the longer glass tube is then 

 connected with a hydrogen generator and hydrogen is 

 allowed to bubble through the gelatin (Fig. 35, A) in 

 the tube until all contained air has been expelled and 



