ANAEROBIC METHODS 131 



4. Displacement of air by means of an air-pump and allowing 

 hydrogen to enter the vacuum. 



Under \hzfirst method we may either exclude oxygen by laying 

 sheets of sterile mica or a cover-glass on the surface of the agar 

 or gelatine plates (Fig. 34), thus excluding air, or deep punc- 

 tures may be made in tubes half filled with gelatine or agar, for 

 growths often occur in the depths of the medium, especially if 



FIG. 35. Novyjar. 



the latter has been boiled previously to expel the oxygen; or, 

 instead of mica, sterile paraffine may be poured over the top of 

 the tube. The layer of paraffine excludes the air. Flasks filled 

 with bouillon, or tubes filled with bouillon, or melted agar may be 

 inoculated with an anaerobic culture, but the filling of the vessel 

 with the medium must be absolute so that no space is left for air, 

 otherwise the organisms may not grow. Roux employs a long 

 sterile glass tube, which he completely fills with melted agar 



