38 



MICRO-ORGANISMS AND FERMENTATION. 



These flasks must only be opened in a sterile cupboard. 

 When gelatine is used the flask must be opened with the mouth 

 downward. 



For special purposes the Hansen flask (Fig. 7, left) is 

 employed. The ground cap is provided with a cotton-wool 

 filter, and the flask has a small side-tube closed with an asbestos 

 stopper. This flask is used in the author's laboratory for the 

 dispatch of small cultures or of samples from the propagating 

 apparatus.* For this purpose the lower part of the flask is 

 filled with cotton-wool, and some cotton-wool is lightly packed 

 into the cap. The asbestos stopper and the lower edge of the 

 cap must be covered with sealing wax. 



A flask (Fig. 7, right, and Fig. 8) constructed by the author 



n 



carries a small, bent, and open tube in the cap, as a prolongation 

 of the cotton-wool filter. By this means it has proved possible 

 to prevent the evaporation of the contents of the flask for 

 several years, provided that the lower edge of the cap and also 

 , the lateral tube are well closed. This flask is used for pre- 

 serving pure cultures of yeast in a 10 per cent, saccharose 

 solution inoculated with a trace of the yeast. The flask is 

 also suitable for a prolonged preservation of gelatines, if the 

 surface is to be prevented from stiffening. Another flask 

 constructed by the author, shown in section in Fig. 9, is also 

 used for storing pure cultures of bottom and especially of top 

 yeasts which will not stand vigorous shaking ; when further 



* This apparatus is described in Chapter vi. 



