44 A MANUAL OF BACTERIOLOGY 



point nipped off, and the open end dipped beneath 

 the surface of the culture fluid. As the bulb cools 

 the fluid is drawn into it. The neck of the bulb 

 is again sealed, and the fluid contained therein is 

 sterilised by repeatedly boiling the bulb in a water- 

 bath. It is then placed in an incubator for three 

 or four days. If the contents remain transparent 

 and clear, there is no doubt that the fluid has 

 been properly sterilised. Many of these bulbs, 

 containing sterilised bouillon, should be kept in 

 stock. 



It may be mentioned that Chamberland's tube 

 (Fig. 17 c) is filled and sterilised in the same 

 way as Sternberg's bulb. 



Sir Joseph Lister's flask (Fig. 17 N) is used for 

 the storage of culture fluids. The fluid is introduced 

 into the flask, the neck plugged with cotton-wool, 

 and the fluid sterilised by repeated boiling. When 

 a portion of the sterile fluid is required, all that 

 is necessary is to pour it through the lateral arm of 

 the flask : this is done by simply tilting the flask. 

 When the flask regains its erect position a drop of 

 the fluid remains behind in the fine opening of the 

 arm ; and thereby prevents the regurgitation of 

 unfiltered air. After the removal of a portion of 

 the fluid, a cap of cotton- wool is tied over the lateral 

 opening, and the residue in the flask is kept for 

 future use. 



Aitken's tube (Fig. 17 E) is a modification of the 

 ordinary test-tube. It has a lateral arm whose ex- 

 tremity is hermetically sealed. The nutrient fluid 

 is introduced through the open end of the tube, 



