382 



ENERGY LOSS AND BIOLOGICAL EFFECTS 



recessive defects. Detailed and statistical studies are needed to obtain 

 the exact shapes of the survival curves. One might ask what the survival 

 curves would look like if the medium on which the cells grow were 

 changed in composition. There is some preliminary evidence that the 

 shapes of the survival curves change for a medium different from the 

 one used in this study. Such a change is expected because it is assumed 

 that a cell may have more than one mechanism available to produce the 



100 



80 



60 



40 



20 







20 



100 



40 60 80 



X-ray dose, krep 



Fig. 16. Experimental survival curves of a diploid colony with about three unpaired 

 defects. This colony was obtained by preirradiation subsequent to isolation of a 

 single cell and its growth into a vegetative colony. The survival of a normal diploid 



colony is also shown. 



essential components for division. One would expect the maximum 

 number of essential sites on a minimum medium for survival, whereas 

 on a more complex medium it would be anticipated that the number of 

 essential sites might be decreased. There is hope that the studj^ of such 

 cells will furnish important clues for the biochemical defects present in 

 each cell. This information should be of value in the interpretation of 

 the basic mechanism of cell division. 



Conclusions 



1. A parallelism is demonstrated between the so-called indirect 

 mechanism of radiation effect and the hit theory. 



2. The apparent contradiction in the two theories may be eliminated 

 by using the "diffusion model" of radiation effects. This model assumes 

 the formation of intermediates by the ions of the primary radiation. 

 These may migrate in the cell and chemically interact with genie and 

 extragenic components. 



