VARIATIONS IN THE SACCHAROMYCETES. 289 



be of a stable character both when applied on the large scale, 

 and also when stored for years in a 10 per cent, cane-sugar 

 solution. There are variations still kept in the laboratory 

 which after preservation in such a solution for more than ten 

 years still retain their properties. These races, therefore, 

 do not disappear. 



It follows that in the preparation of pure cultures in yeast 

 to be applied in a brewery, a distillery, a wine fermentation, 

 etc., we cannot reckon on dealing simply with a type ready to 

 hand in a pure condition, but rather with a mixture of elements, 

 often of a highly different character, even if the mass of yeast 

 has been originally derived from a single cell. By the process 

 of pure cultivation based upon a detailed knowledge of the 

 special practical requirements, a form can be prepared of 

 the required type. Such work can never be attempted at 

 random, but must consist of systematic research carried out 

 with rigid rules. How long such a type may be preserved 

 in practice before it develops such pronounced varieties 

 and in such quantities that the character of the yeast mass 

 experiences a change, depends to a great extent upon circum- 

 stances which are still unknown. 



It will be seen from all this that the principle applied in 

 the author's laboratory in carrying out the pure culture of 

 brewery, distillery, and wine yeasts, etc., is based on a reliable 

 starting point, and the experience gained during the long 

 time that has elapsed since the laboratory was instituted 

 has only served to confirm the correctness of the author's 

 view. 



The improvement of yeast, about which the author has 

 published his views, consists in selecting cells taken from a 

 mass of yeast which has given satisfactory results, and pre- 

 paring growths which display the desired characters in greatest 

 perfection. This treatment is carried on through several 

 generations, and in each case after the mass of yeast has been 

 applied for some time in practice. 



These observations have no connection with any variation 

 in the composition of a nutritive fluid. They are simply 

 concerned with comparative experiments with selected and 

 absolutely pure cultures. 



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