262 MICRO-ORGANISMS AND FERMENTATION. 



again connected with a Pasteur flask containing wort, and the 

 yeast is rinsed into the latter. 



This method has proved valuable for sending absolutely 

 pure yeast to tropical countries, rendering it possible to send 

 large collections of pure cultivations to Australia, South 

 America, and the most distant Asiatic countries at small 

 expense. 1 



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. In 

 such a solution cultivated yeasts can be kept alive for years. 2 



The absolutely pure and systematically selected races of 

 yeast, prepared in large quantities for industrial purposes, are 

 now employed in numerous breweries in all beer-producing 

 countries, not only in Europe, but also in America, Asia, and 

 Australia. HANSEN made his first experiment in 1883 in the 

 well-known Old Carlsberg brewery at Copenhagen. 



Since HANSEN'S system was first carried out in a bottom- 

 fermentation brewery, it naturally found its first application in 

 breweries of the same kind, and in these it has reached the 

 highest degree of perfection. Any one who wishes to become 

 acquainted with the application of this system to one or other 

 branch of the fermentation industries, should therefore take, 

 as the starting-point of his studies, the results achieved in bottom- 

 fermentation brewing. 



The first pure cultivated and methodically selected high- 



1 The use of sterilised filter-paper for sending yeast samples is for quite a 

 different object. This method is used for sending an impure brewery yeast to 

 a laboratory in order that a pure culture may be prepared from it. 



2 It is not advisable to preserve ferment-organisms on gelatines. Thus 

 P. FRANKLAND observed that fermentation bacteria may lose their fermen- 

 tative power more or less completely if cultivated for a considerable length 

 of time on a solid medium ; sometimes the fermentative power disappeared 

 after one single 'cultivation. The same result was obtained by NENCKY with 

 regard to certain lactic acid bacteria. The writer has shown that high- 

 fermentation yeasts in use in breweries lose some of their most valuable 

 practical properties by cultivation on wort-gelatine, for cultures developed 

 from such materials clarified less readily and effected too active a fermentation. 



