MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 21 



neck of which is closed with a ground cap, which terminates 

 above in a short, open tube ; this tube is filled with tightly- 

 packed sterilised cotton-wool. 



The Freudenreich flask is constructed on exactly the same 

 principle ; it has, however, a cylindrical shape. 



For certain special purposes Hansen's flask (Fig. 5) is em- 

 ployed. The ground cap is provided with a cotton-wool filter 

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



FIG. 5. HANSEN Flask. FIG. 6. 



stopper (d). This flask is used partly for the preservation of 

 pure cultures, partly for sending small cultures or samples from 

 the propagating apparatus. 1 For the first-named purpose the 

 flask is half filled with a 1 per cent, solution of cane-sugar, 

 to which a trace of the yeast-culture is then added. The 

 asbestos stopper and lower edge of the cap is coated with seal- 

 ing-wax (c). For the last-named purpose the lower part of the 

 flask is filled with cotton-wool (e), and some cotton-wool (b) is 

 also put into the cap, below the filter. For the method adopted, 

 see Chapter VI. 



A modification of this flask has been constructed by the 

 author (Fig. 6) by placing a small bent tube in the cap, as an 

 immediate prolongation of the cotton-wool filter. By this 

 means it has been possible to prevent the evaporation of the 

 contents of the flask for several years, provided that the lower 



1 For the description of this apparatus, see Chapter VI. 



