112 K. V. KossiKOv 



but also of maltose. Attention should be drawn to the fact 

 that both these cultures developed from the same cell, which 

 formed a 4-spore ascus. All 4 spores of this ascus germinated 

 and produced cultures designated as cultures 72/349, 73/349, 

 74/349 and 75/349, respectively. 



During a series of four variants of experiments on adapt- 

 ation to fermentation of sucrose, culture 72/349 became 

 adapted to fermentation of this sugar. However, it developed 

 the ability to ferment both sucrose and maltose in only one 

 of the four variants. During a series of six variants of our 

 experiments, culture 73/349 became adapted to fermentation 

 of sucrose, and in all six cases it developed the ability to 

 ferment both sucrose and maltose. Cultures 74/349 and 

 75/349, in one instance each, became adapted to fermentation 

 of sucrose, and in both instances failed to ferment maltose. 

 Out of 13 hybrid cultures, only one (153/3), when cultivated 

 on sucrose, proved to have become adapted to fermentation of 

 both sucrose and maltose. 



But one cannot, in this case, speak of an accidental varia- 

 tion of fermentative properties of yeast cells, independent of 

 the substrate. The fact is that the effect of sucrose on the 

 yeast cell is conditioned by the biochemical structure of the 

 sugar. Sucrose is composed of 2 monosaccharides, glucose and 

 fructose. Invertase acts in the same way as p-D-fructosidase; 

 but sucrose can be split also by a-glucosidase (maltase) : under 

 certain conditions, maltase can hydrolyse not only maltose 

 but also sucrose. Therefore, it is reasonable to expect that 

 sucrose, which consists of glucose and fructose, can stimulate 

 the formation not only of fructosidase but also of glucosidase. 

 This is confirmed by experimental data obtain by the present 

 author. Yeast cultures which fermented both sucrose and 

 maltose failed to ferment raffinose, indicating that the enzyme 

 a-glucosidase was present in the cells of these cultures. Cultures 

 which fermented only sucrose (and not maltose) fermented one- 

 third of the total amount of raffinose, indicating that the enzyme 

 P-D -fructosidase was present in the cells of these cultures. 

 These data led us to conclude that in the yeasts investigated 



