138 



Discussion 



of mutants would have equalled the number of initial cells. Had the 

 propagation coefficient of mutants been twice as large, the number of 

 both groups would have become the same after 40 generations, i.e. in less 

 than 2 days. However, to attain full adaptation to every consecutive 



06 10 1-5 20 25 



B u t a n 8 . Vo 



Fig. 2 : Adaptation of CI. aceto- 



hutylicum to increased concentrations 



of butanol. Before sporulation. 



concentration of butanol, it required from 460 to 1,500 generations, 

 i.e. from 20 to 70 days (Table I). 



At first, the increased resistance was not transferred through spores. 

 Later on it became so stable that it was retained by cells growing from 

 the spores on the butanol-free medium and then seeded in the vegetative 

 state in media containing different concentrations of butanol (Fig. 3). 



Owing to a shortage of time I shall not refer to other experiments 

 which consisted of adapting Bad. megaterium to greater concentrations 

 of norsulphazol. In this case adaptation took place more easily and more 

 quickly than in the case of butanol. Only 70 reseedings were needed to 

 obtain a fivefold increase in resistance. Simultaneously, sulphazol- 

 dependent forms could be detected in the population. In the case of 

 butanol no such phenomenon could be seen. An increased resistance 

 began to be transmitted through spores. 



In our opinion, these experiments show the possibility of stabilizing 

 adaptive, non-hereditary changes and of their gradual transition to 

 stable hereditary changes. 



