98 RESEARCHES ON YEASTS. 



struggle for the upper hand the one form was more vigorous 

 than the other. In this case the difference was not so marked 

 as in that first described. On further cultivation in wort it 

 completely disappeared, the newly-formed cells again taking 

 the oval form. 



In one of my papers (1883) referred to above, I described 

 a still more pronounced change in the form of the cells of 

 ordinary brewery yeast into long sausage-shaped cells which 

 occurred under the influence of a certain temperature. As 

 this process, however, is of no practical importance, it will not 

 be described here. 



There are several different ways in which it is possible to 

 act upon yeast cells so that in one case they will produce 

 more alcohol and in another case less than that yielded by 

 the original parent cells. The following examples may 

 suffice : By repeatedly cultivating different species on solid 

 nutrient media (especially gelatine with yeast extract) growths 

 were at length obtained, which produced considerably more 

 alcohol than the original parent cells. On the other hand I 

 have succeeded in transforming the low-fermentation Carls- 

 berg yeast No. I. into a new variety, which produces less 

 alcohol and gives a better clarification at the end of the 

 principal fermentation than the primitive form. The process 

 employed in that case was a prolonged cultivation in wort 

 at the temperature of 32 C, each culture being left at rest. 

 The practical bearings of these experiments will be under- 

 stood without further explanation. 



Saccharomyces Pastorianus L is, as already mentioned, 

 one of the disease yeasts of beer, to which it imparts an 

 offensive odour and a disagreeable bitter taste. According to 

 Mach and Portele's investigations, however, it gives a good 

 wine ; and my own experiments have shown that when this 

 species is cultivated for a number of generations in a solution 

 of cane-sugar in yeast water, a growth is obtained the cells of 

 which have for the time lost the disagreeable properties 

 referred to. From this it is seen that it is possible to act 



