SYSTEMATICALLY SELECTED YEASTS. 73 



is then easily poured into the latter. For these reasons I 

 employ a strong, but moderately small flask constructed 

 in accordance with the following description : 



It has a capacity of I 5-2 liters, is made of thick glass, 

 and has a flat bottom (Fig. 15), so that no support is required. 

 Fig. 1 6 shows a longitudinal section of the straight tube ; c is 

 a glass tube, the end of which is provided with a slightly 

 raised collar ; b is a tightly fitting rubber stopper ; a is a stout 

 indiarubber cap stretched over b, and bound at d with copper 

 wire (the binding is shown in Fig. 15). The rubber stopper 

 (Fig. 16, b) must not only fit very accurately, but it should also 

 be moderately easily withdrawn when the cap a is removed. 

 An indiarubber tube (Fig. 15, b) fitted at its lower end to a 

 glass tube c is fixed to the bent neck of the flask d. The 

 rubber tube b must be strong, and should be bound with wire 

 over the two glass tubes ; near the mouth of the bent neck is 

 a pinch-cock, by means of which the rubber can be completely 

 closed. The glass tube c, which becomes somewhat narrower 

 towards its lower end, contains a cotton-wool filter. 



The cotton-wool pressed into this tube should not be in 

 excess of that required to prevent atmospheric germs from 

 entering the flask whilst its contents are being poured out 

 through the straight tube a, Fig. 15. The object of the filter 

 is to obviate the use of a flame. The parts made of rubber 

 are sterilised by boiling in water or by heating in steam, the 

 rest by heating for two hours at about 150 C., the ends of the 

 two tubes being first plugged with cotton-wool. As the flask 

 is made of thick glass, it is necessary to be very cautious in 

 heating it ; it should be placed upon a cork block, which, 

 again, rests on a sheet of asbestos, and care must be taken 

 that there is no great difference in the temperature at the top 

 and bottom of the sterilising oven. When cold, the cotton- 

 wool plug is removed from b, Fig. 15, and the rubber tube, 

 pinch-cock, and filter-tube are joined together as quickly as 

 possible. 



