130 K. V. KossiKOv 



adapted form did not prove to be very viable, but propagated 

 more or less normally for some time in very strictly defined 

 conditions. In inadequate conditions, not only does this form 

 lose its acquired property (reversion), as one would expect, 

 but it dies off altogether. This form can become viable only 

 if some new quaUtative change occurs in it. To the same type 

 of variation belong 10 cultures out of 29 obtained from single 

 spores ofS. paradoxus 37, adapted to fermentation of maltose; 

 3 out of these 10 cultures developed (on wort-agar) stable 

 colonies which readily ferment maltose. 



The third type of variation is characterized by the appearance 

 in the cells (under the influence of the specific substrate) of the 

 so-called adaptive enzymes which are produced only when 

 there is an adequate specific substrate in the medium. If the 

 specific substrate is removed from the medium the cells no 

 longer produce the enzyme, and they lose their acquired 

 property. This type of variation is known to exist among 

 yeasts of the genus Saccharomyces during their adaptation to 

 fermentation of galactose and mehbiose. One would think 

 that during prolonged cultivation on the medium with the 

 adequate sugar (as the only source of carbohydrate), cells 

 would develop which could retain the abihty to produce an 

 adequate enzyme, the specific substrate being absent from the 

 medium. 



The fourth type of variation is that where cells retam the 

 acquired abihty to produce an active enzyme, ferment an 

 adequate sugar and transmit this capacity to the progeny 

 after reseeding into media not containing this sugar. In sexual 

 reproduction (spore formation) the altered cells become segre- 

 gated. An example of this is found in the adaptation of 

 S, globosus to fermentation of sucrose and maltose, and of 

 S. paradoxus to fermentation of maltose. 



Experiments to determine quantitatively the sucrose- 

 fermenting activity of invertase in original cultures of S. glo- 

 bosus, in heterozygous cultures adapted to fermentation of 

 sucrose and in homozygous cultures (these last being obtained 

 from heterozygous cultures through spore formation), gave 



