CULTURES OF AN/EROBES IN LIQUID MEDIA. 73 



to place in the tube, through which the hydrogen is to be 

 delivered, a little plug of cotton wool. The flask being 

 thus prepared, it is sterilised by methods B (2) or B (3). 

 On cooling it is ready for inoculation. In the case of the 

 flask with the lateral nozzle, the cotton-wool covering having 

 been momentarily removed, a wire charged with the organ- 

 ism is passed down to the bouillon. In the other kind of 

 flask the stopper must be removed for an instant to admit 

 the wire. The flask is then connected with the hydrogen 

 apparatus by means of a short piece of sterile india-rubber 

 tubing, and hydrogen is passed through for half an hour. 

 In the case of flask (i), 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 disconnected from the hydrogen ap- 

 paratus. In the case of 

 flask (2), first the exit 

 tube and then the en- 

 trance tube are sealed 

 off in the flame before 

 the flask is disconnected 

 from the hydrogen ap- 

 paratus. It is well in the 

 case of both flasks to 

 run some melted paraffin 

 all over the rubber stop- 

 per. Sometimes much 

 gas is evolved by anae- 

 robes, and in dealing 

 with an organism where 

 this will occur, provision 

 must be made for its escape 



FIG. 24. Flask arranged for culture of 



anaerobes which develop gas. 



b is a trough of mercury into which exit 



tube dips. 



This is conveniently done 



by leading down the exit tube, and letting the end just 

 dip into a trough of mercury (Fig. 24), or into mercury 

 little bottle tied on to the end of the exit tube. 



m a 



The pressure of gas within causes an escape at the mercury 

 contact, which at the same time acts as an efficient valve. 



