130 BACTERIOLOGY 



bottom of the Novy jar. 1 On top of the stack of Petrid is hesis 

 placed a small flask containing strong solution of sodium hydrox- 

 ide, and provided with a siphon spout ( see Fig. 56). A rub- 

 ber is attached to this spout and leads down to the floor of the 

 jar. After hydrogen has been passed through the jar and it 

 has been finally closed, a 'slight tipping to one side starts the flow 

 of the alkali through the siphon and so makes the pyrogallic acid 

 available to absorb the last traces of oxygen. 



Further Anaerobic Methods. Numerous other expedients 

 have been employed for the cultivation of anaerobes. Koch 

 covered part of the surface of a gelatin plate with a bit of steril- 

 ized mica or a cover-glass. Such a method suffices to prevent the 

 growth of strictly aerobic forms but rarely suffices for the success- 

 ful culture of strict anaerobes. Covering the surface of the med- 

 ium with sterile liquid paraffin is a more perfect means of exclud- 

 ing air. 



In all anaerobic culture methods, the presence of one or more 

 reducing substances in the culture medium is of great importance. 

 Those commonly employed are glucose, litmus and native protein. 



1 MacNeal, Latzer and Kerr, Journ. Infect. Diseases, 1909, Vol. VI, p. 557. 



