VARIATION OF SPECIES 185 



studied the effect of fluorides and hydrofluoric acid on yeasts. A 

 special concentration exists where the vegetative growth is greatest, 

 and also where the fermenting activity is greatest. These two optima 

 do not coincide. When the fermenting power is greatest, the vegeta- 

 tion is absent. Dienert, 1 in about the same manner, has shown that 

 when yeasts which ferment galactose actively are placed in a saccharose 

 solution and eventually, after washing, are placed in galactose, they fail 

 to induce a fermentation quickly. Only after from 24 to 36 hours is 

 a typical fermentation started. If the same experiment is repeated 

 with the exception that galactose replaces the saccharose, the fer- 

 mentation will start in about an hour. The time for fermentation to 

 start is thus greatly shortened. By the latter treatment, the yeast 

 has been " accustomed " to the galactose by the preliminary treat- 

 ment. 



These results compare with investigations of Duborg. 2 It is known 

 that the greater number of the yeasts are able to ferment galactose. 

 Duborg has been able to train yeasts, which normally do not ferment 

 this sugar, to ferment it. He cultivated his yeasts in a liquid very 

 rich in carbohydrate materials (yeast water, 25 per cent, glucose 5 

 per cent and galactose 5 per cent). It is the cultivation of the yeast 

 in this solution in the presence of galactose which gives it a power 

 which it did not possess. The more recent investigations of Harden 

 and Norris 3 have confirmed these data. 



An increase in the activity of zymase may also be explained by 

 these data. Duborg has gone still further. He claims that a yeast 

 which does not invert cane sugar may be made to do so by cultivating 

 it in a nitrogenous medium containing dextrose and saccharose. This 

 statement has been refuted by Klocker and Hansen who claim that a 

 yeast which does not ordinarily decompose sucrose cannot be made 

 to do it. According to these authors 4>5 the possession of invertase is 

 a constant characteristic and useful in the determination of the yeasts. 



Other investigations on physiological variations have been carried 



1 Dienert, G. Sur la fermentation de la galactose et 1'accoutumance des 

 levures a ce sucre. Ann. Inst. Past. 14, 1900. 



2 Duborg, E. De la fermentation des Saccharides. Comp. Rend. Acad. 

 des Sciences, 128, 1899. 



3 Harden, A. and Norris, R. The fermentation of galactose by yeast and 

 yeast juice. Proceedings of the Royal Society, 82, 1910. 



4 Klocker, A. La formation des enzymes dans les ferments alcooliques peut- 

 elle servir a caracteriser 1'espece? Comp. Rend. lab. de Carlsberg, 50, 1909. 



5 Hansen, E. C. Recherches sur la physiologic et la morphologic des ferments 

 alcooliques. XI. La spore de saccharomyces devenue sporange. Recherches 

 comparatives sur les conditions de vegetative croissance et le developpement des 

 organes de reproduction des levures et des moisissures. Comp. Rend, du lab. 

 de Carlsberg, 5, Book 2, 1902. 



