184 VARIATION OF SPECIES 



Physiological Variations: Besides morphological variations, one 

 may also observe physiological variations. A yeast may, for example, 

 under certain conditions, induce more or less active fermentations in 

 the same way that a bacterium may be made more or less virulent. 

 But while certain bacteria, Bacillus anthracis for instance, may be 

 made avirulent, among the yeasts it is impossible to suppress the fer- 

 menting function. One may decrease it or even increase it but not 

 entirely blot it out. 



The first investigations on variation of physiological nature in 

 yeasts were carried out by Hansen. When cultivating two races of 

 Saccharomyces carlbergensis for a long time in two series, one on ordinary 

 beer wort and the other on the same substance to which gelatin had 

 been added, he was able to build up a more actively fermenting type 

 on the gelatin medium. By cultivating the ascospores of Saccharo- 

 myces cerevisiae in gelatin with yeast water, the same investigator ob- 

 tained a variety which would form from one to three per cent more 

 alcohol than the original culture. On the other hand, by cultivating 

 Saccharomyces carlbergensis in must at 32 C. Hansen has obtained a 

 variety which formed less alcohol than the normal. According to 

 Hansen, these results are due to a selection born of a transformation. 

 The most active type will tend to be built up. From all of these 

 examples which we have mentioned one is justified in concluding that 

 cells of the same species of yeast often present great differences and 

 that new varieties may be created by selection which have special 

 physiological properties. 



This is the point of departure from the use in the industries of 

 " selected yeasts." By making a series of cultures from a single cell, 

 as each cell possesses slightly different physiological properties, one 

 may obtain strains presenting the definite properties of the original 

 cell. Some will be more feeble and others more active. The latter 

 have been termed " yeasts by selection " for they may be maintained 

 for a longer or shorter period and are then able to yield the best 

 results in the industries. 



All of the physiological variations which we have just mentioned, 

 increase or decrease of the fermenting function, are abrupt transfor- 

 mations. It is now time to look into the work of Effront and other 

 workers for examples of transformations due to determined causes, 

 as the becoming accustomed to chemicals. 



The work of Beinarcki has shown that the antiseptics in small 

 doses progressively increase the fermenting power of yeast up to a 

 certain limit where the yeast degenerates and dies. There are, then, 

 doses which " favor " this ability up to certain limits. Effront l has 



1 Effront, J. L'influence de 1'acide fluorhydrique et des fluorures sur lea 

 levures de biere. Comp. Rend. Acad. Sciences, 117, 1893; 118 and 119, 1894. 



