420 MICRO-ORGANISMS AND FERMENTATION. 



of pure cultures to the most distant countries at a very small 

 cost. 



It is of the greatest importance to note that, even after 

 the lapse of years, the particular yeast once selected can 

 always be procured again, a sample of the pure culture being 

 preserved in the laboratory in a 10 per cent, solution of cane 

 sugar, kept in the flasks described in Chap. i. (p. 37), devised 

 by the author for the purpose. Culture yeasts may be kept 

 alive in such a solution for years without any alteration in 

 their properties. It is of importance, in order that the culture 

 yeasts may be kept unaltered for a long time, that the layer 

 of yeast deposited upon the bottom of the flask should not 

 be frequently shaken. During the introduction of a few 

 drops into a Pasteur flask shaking can only be avoided by 

 the use of the flask depicted in Fig. 9. With any other variety 

 it is necessary to maintain a number of flasks for each species 

 of yeast, and each one will only serve for a few infections. 

 On the other hand, no effect of temperature has been observed 

 during storage, and the dilution of the liquid can be avoided 

 by the use of the two flasks constructed by the author, and 

 shown in Figs. 8 and 9. All physiological laboratories con- 

 cerned with fermentation possess such collections of preserved 

 growths. The author's collection of species which have been 

 gradually introduced into practice dates back to the year 

 1884, and numbers many thousands of specimens. A few of 

 these species have retained those properties which are of indus- 

 trial value for more than ten years. According to Hansen's 

 and the author's experiments yeasts may be kept alive under 

 such conditions for a much longer period. 



Regarding the storage of dried yeasts on the large scale, 

 A. Will has made extensive investigations, the results of which 

 will be found in the technical literature. 



