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DISCUSSION 



Yudkin : Part of the explanation of these results may be that it is the 

 same sort of phenomenon as that which we have found with Esch. coli, 

 with proflavine resistance. If we assume that in Prof. Kunicki- Gold- 

 finger's experiment, during the actual cooling in buffer the cells reach a 

 stage of synchronization, and if we assume that there is a change in the 

 resistance to streptomycin, as to proflavine, at different times during 

 division then it may be that the increase in resistance on taking the cells 

 from the cooled buffers expresses the resistance at a particular stage in 

 the resistance cj^cle. 



Kunicki-Goldfinger : I cannot agree with that, because you can obtain 

 synchronization of growth after a few hours of cooling, whereas the in- 

 crease in resistance is obtained only after very many hours; after 24 

 hours this increase is not yet complete. There is no correlation in time 

 between this phenomenon of synchronization and the increase in the 

 number of resistant cells. 



Yudkin: How did you test for synchronization? 



Kunicki-Goldfinger: By direct observation of the time of division of 

 500 cells on the surface of the agar. A long time was needed for these 

 observations, but I think that they are convincing. 



Yudkin: The degree of synchronization is extremely high, much higher 

 than has ever been previously reported. 



Kunicki-Goldfinger: It is very high. The first and the second division 

 are not quite synchronized. 



Yudkin: That too is unusual, because in general the degree of syn- 

 chronization falls very rapidly. 



Stocker: Perhaps this elegantly investigated phenomenon is one 

 example of a general phenomenon which the geneticists usually ignore, 

 because it is inconvenient. If we compare the logarithmic phase cells 

 (i.e. cells growing in a rich medium) with resting phase cells (i.e. starved 

 cells) we know they differ phenotypically in their resistance to penicillin 

 and in a variety of other characters. It is commonly assumed, as a first 

 approximation, that we can regard all populations of cells in exponential 

 growth as being similar, regardless of whether they have been in ex- 

 ponential growi:h for some generations or whether they have only recently 

 come back into exponential growth. One has encountered evidence that 

 this is certainly not the case in particular instances; for instance, with 



