46 A MANUAL OF BACTERIOLOGY 



on which is a Mohr's clip, and to the other end 

 of this tubing is fitted a piece of glass tubing 

 with a constricted orifice. A plug of carefully 

 sterilised cotton wadding is pushed into the thistle- 

 head, the india-rubber stopper is pushed into the 

 neck of the flask, and then a sheet of cotton 

 wadding is placed over the whole of the tubes 

 and the mouth of the flask, and is held in position 

 by an india-rubber band. The flask is placed in a 

 steam steriliser, where it may be left for a sufficient 

 length of time to allow of it becoming perfectly 

 sterilised. It is filled nearly a third full with 

 bouillon or gelatine, after carefully removing the 

 sheet of wadding and the stopper ; these are then 

 replaced, and the whole is again sterilised as usual. 

 When the gelatine or bouillon is to be drawn off 

 into test-tubes, the flask is inverted and held in a 

 retort stand, the sheet of wadding is carefully re- 

 moved and folded, the glass nozzle is inserted into 

 the mouth of the test-tube, the clip is opened and 

 the gelatine or bouillon escapes ; all the air passing 

 into the flask, being filtered through the wadding 

 in the thistle-head tube, is thoroughly sterilised. 

 If the whole of the gelatine or bouillon is not with- 

 drawn, all that is necessary is to replace the sheet 

 of wadding (care having been taken to preserve 

 the inner surface, by folding it inwards). There is 

 no necessity to sterilise after this has been once 

 done, all that is necessary subsequently is to heat 

 sufficiently to render the peptonised gelatine fluid ; 

 but this is not required if the stock flask con- 

 tains bouillon. This apparatus is specially useful 



