62 METHODS OF CULTIVATION OF BACTERIA 



flask (1), the lateral nozzle is plugged with molten paraffin 

 covered with alternate layers of cotton wool and paraffin, the 

 whole being tightly bound on with string. The entrance tube 

 is now completely drawn off in the flame before being dis- 

 connected from the hydrogen 

 apparatus. In the case of 

 flask (2), first the exit tube 

 and then the entrance tube 

 are sealed off in the flame 

 before the flask is discon- 

 nected from the hydrogen 

 apparatus. It is well in the 

 case of both flasks to run 

 some melted paraffin all over 

 the rubber stopper. Some- 

 times much gas is evolved by 

 anaerobes, and in dealing 

 with an organism where this 

 FIG. 25.-Flask arranged for culture of will occur prO vision must be 

 anaerobes which develop gas. i < rp, . 



b is a trough of^rcmy into which exit is conve niently done by lead- 

 ing down the exit tube, and 



letting the end just dip into a trough of mercury (Fig. 25), 

 or into mercury in a little bottle tied on to the end of the 

 exit tube. The pressure of gas within causes an escape at the 

 mercury contact, which at the same time acts as an efficient 

 valve. The method of culture in fluid media is used to obtain 

 the soluble products of such anaerobes as the tetanus bacillus. 



FIG. 26. Tubes for anaerobic cultures on the surface of solid media. 



When it is desired to grow anaerobes on the surface of a 

 solid medium such as agar, tubes of the form shown in Fig. 26, 

 a and b, may be used. A s'troke culture having been made, the 

 air is replaced by hydrogen as just described, and the tubes are 

 fused at the constrictions. Such a method is of great value 



