108 K. V. KossiKOV 



lactose acquired the capacity to ferment sucrose, the addition 

 of sucrose to the medium would cause reproduction to occur. 

 The same might occur in the corresponding case of a culture 

 maintained on sucrose. 



On the seventeenth day after addition of fresh medium to 

 the test-tubes (during which time four more cultures had 

 become adapted to fermentation of sucrose), cells from these 

 test-tubes were transferred to those provided with gas-traps 

 and fresh medium. The cultures which were kept initially on 

 sucrose medium, and to which we added 2-0 ml. of a medium 

 with lactose, were now transferred to the medium containing 

 6 • per cent lactose and • 4 per cent autolysed yeast extract. 

 Cultures initially kept on lactose medium, and to which we 

 had added 2 • ml. of a medium with sucrose, were now trans- 

 ferred to the medium containing 6 per cent sucrose and 0-4 

 per cent autolysed yeast extract. Observation of fermentation 

 was continued for a further 28 days. Therefore, each culture 

 initially seeded into the sucrose medium could develop on the 

 medium in the presence of lactose for a 45-day period following 

 the 208-day cultivation on sucrose. If lactose-fermenting 

 cells had developed in such cultures, they would have started 

 fermenting this sugar; however, no cultures were detected 

 which had adapted to fermentation of lactose. 



Somewhat different results were obtained in the work with 

 cultures initially kept on the lactose medium and later 

 transferred to the sucrose medium. It was to be expected 

 that, in this case, during the 45 -day cultivation period of 

 experimental cultures on the medium with sucrose, cells 

 would develop which would be adapted to fermentation of 

 sucrose. The essential question, however, was: on which day 

 after the contact with sucrose did fermentation begin, and 

 how many fermenting cultures appeared? In fact, of the 221 

 cultures, only 2 were found to be adapted to fermentation of 

 sucrose; and one of these started fermenting sucrose on the 

 twenty-eighth day, and the other on the thirtieth day after 

 contact with sucrose. This experiment shows that, during 

 cultivation on lactose, no cells developed which were capable 



