Induced Mutational Changes in Yeast 107 



221. The test-tubes in the experiment were kept under 

 observation for 225 days. 



During the first three days shght fermentation was ob- 

 served in all the test-tubes, as evidenced by a slight evolution 

 of carbon dioxide resulting from glucose fermentation. On the 

 fourth to fifth day fermentation ceased. A certain amount of 

 carbon dioxide accumulated in the gas-traps of almost every 

 test-tube (occupying not more than one-twentieth the volume 

 of the gas-traps). 



Further observation of fermentation was made, the control 

 starting-point being a notch on the wall of the test-tube. If 

 amount of carbon dioxide in the gas-trap tended to increase, 

 it was assumed that fermentation had occurred due to 

 adaptation of a culture to fermentation of sucrose or lactose, 

 respectively. On the twenty-eighth day following seeding, an 

 increase was noted in the amount of carbon dioxide in the gas- 

 traps of two of the test-tubes which contained sucrose. 

 Another culture began to ferment sucrose on the eighty-fourth 

 day. In order to ascertain whether what had occurred in this 

 experiment was really the adaptation of cells of a given 

 culture to the fermentation of sucrose, the fermented culture 

 was reseeded onto the medium with sucrose, without adding 

 glucose. It was believed that in the three-stage consecutive 

 fermentation of sucrose by the adapted culture, certain cells 

 developed which transmit this quality of fermentation to the 

 progeny. In the course of 208 days, another 21 cultures of 

 cells were seen to have started fermenting. None of the cul- 

 tures trained on lactose became adapted to fermentation of 

 this sugar during the same period of time. 



Fresh medium (2-0 ml.), consisting of 6 per cent sucrose 

 and 0-4 per cent autolysed yeast extract, was added to the 

 test-tubes containing lactose, 208 days after commencement of 

 the experiment. Fresh medium (2-0 ml.), consisting of 6 per 

 cent lactose and 0-4 per cent autolysed yeast extract was 

 added to the test-tubes containing sucrose. This was the 

 commencement of tests for spontaneous changes. It was 

 assumed that if even one single cell in a culture maintained on 



