72 METHODS OF CULTIVATION- OF BACTERIA. 



and agar can be used in the same way if the medium 

 is heated to boiling-point before use to expel any absorbed 

 oxygen. 



Cultures of Anaerobes in Liquid Media. It is necessary 

 to employ such in order to obtain the toxic products of the 

 growth of anaerobes. Glucose broth is most convenient. 

 It is placed either (i) in a conical flask with a lateral open- 

 ing and a perforated india-rubber stopper, through which a 

 bent glass tube passes, as in Fig. 23, #, by which hydrogen 

 may be delivered, or (2) in a conical flask with a rubber 



FIG. 23. 



a. Flask for anaerobes in liquid media. Lateral nozzle and stopper fitted for 

 hydrogen supply, b. A stopper arranged for a flask without lateral nozzle. 



stopper furnished with two holes, as in Fig. 23, &, through a 

 tube in one of which hydrogen is delivered, while through 

 the tube in the other the gas escapes. The inner end of 

 the gas delivery tube -must in either case be below the 

 surface of the liquid ; the inner end of the lateral nozzle 

 in the one case, arid the inner end of the escape tube in the 

 other, must of course be above the surface of the liquid. 

 The single tube in the one case and the two tubes in the 

 other ought to be partially drawn out in a flame to facilitate 

 subsequent complete sealing. The ends of the tubes 

 through which the gas is to pass are previously protected 

 by pieces of cotton wool tied on them. It is well previously 



