104 K. V. KossiKOv 



cultures. Each culture was first tested for its ability to fer- 

 ment sugars. It was established that none of the cultures 

 selected for the experiment fermented sucrose or maltose 

 during 30 days of cultivation on the nutrient medium, in the 

 presence of 2 per cent of these sugars (these sugars being the 

 only carbohydrate source). 



Special experiments were carried out with the aim of investi- 

 gating the influence of cells which failed to ferment sucrose, 

 on those capable of fermenting this sugar (in a mixed culture). 

 It was found that the presence of non-fermenting cells con- 

 siderably retarded the fermentation of sugar. It is reasonable 

 to expect that, during the process of adaptation, there first 

 appears in the mass of yeast cells a single cell (or a very 

 limited number of cells) which can ferment a specific sugar. 

 If non-fermenting cells retard the reproduction of these 

 particular cells, and thus hinder the demonstration of ferment- 

 ative abilities of the progeny, how long will it take such a cell 

 to propagate sufficiently in these conditions and cause the 

 fermentation of sucrose determinable in the experiment? 



To answer these questions, additional experiments were 

 carried out which enabled us to find the maximal period 

 necessary for detecting — in the mass of sucrose-nonfermenting 

 cells — this one sucrose-fermenting cell. 



These experiments were carried out in test-tubes with 

 gas-traps, on a medium containing 2 per cent sucrose and • 3 

 per cent autolysed yeast extract. S. glohosus 349 was used as 

 the sucrose-nonfermenting culture. The sucrose-fermenting 

 culture was obtained from the adapted cell from the same 

 strain, S. glohosus 349, by cultivating this strain on the 

 medium with sucrose. Preliminary tests showed that the 

 ability to ferment sucrose, developed by this cell, was very 

 strongly heritable. 



In the first series of experiments there were three variants 

 of yeast dilutions, the yeasts being of the sucrose-nonferment- 

 ing type. In the first variant the test-tubes were filled with 

 350-400 million, in the second variant with 3-4 million and in 

 the third variant with 35-40 thousand sucrose-nonfermenting 



