228 



BACTERIOLOGY 



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

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

 surface of the stopper. 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. 38, A) 



FIG. 38 



Franke!' s method for the cultivation of anaerobic bacteria. 



in the tube until all contained air has been expelled and 

 .its place taken by the hydrogen. 1 When the hydrogen has 



1 Before beginning the experiment it is always wise to test the hydro- 

 gen i. e., to see that it is free from oxygen and that there is no danger 

 of an explosion, for unless this be done the entire apparatus may be blown 

 to pieces and a serious accident occur. The agents used should be pure 

 zinc and pure sulphuric acid of about 25 to 30 per cent, strength. With the 

 primary evolution of the gas the outlet of the generator should be closed 

 and kept closed until the gas reservoir is quite filled with hydrogen. The 



