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A MANUAL OF BACTERIOLOGY 



flame, and then the proximal or longer one in the same 

 manner. The rubber cork must, of course, fit well, and 

 the joints should be paraffined. 



For broth or other fluid cultures, which are essential 

 for obtaining toxic products, flasks are used which are 



fitted up like the Frankel 

 tube described above, and 

 the procedure is the same. 



As many anaerobic organ- 

 isms produce gas during 

 their growth, it may be 

 necessary to provide for its 

 escape from a closed flask, 

 or the flask may burst owing 

 to the pressure. This can be 

 done by adjusting a mercury 

 valve. This consists of a 

 small tube or capsule of mer- 

 cury applied to and so sealing 

 an exit tube. The arrange- 

 ment is shown in the accom- 

 panying illustration (Fig. 17) 

 of a " yeast flask " with the 

 capsule of mercury C applied 

 to the end of the exit tube. 

 A is a rubber cork plugging 

 the mouth of the flask, and 

 B is a glass tube through 

 which the hydrogen is passed ; 

 when the air is displaced the capsule of mercury is applied 

 to C and B is sealed off. The flask, with the capsule of 

 mercury applied to the end of the lateral branch, can 

 then be placed in the incubator. The mercury thus forms 

 a valve through which air cannot enter, while gases formed 

 by the growth of the organism have free exit. 



FIG. 17. Yeast flask arranged 

 for anaerobic cultivation. 



