GENETIC AND CYTOLOGIC AL EFFECTS 281 



the effectiveness of some of the wave lengths applied in inducing such 

 alterations. Radiation injury was in general parallel to genetic effective- 

 ness. The data are shown in Table 7-8. 



These data represent the most significant evidence now at hand, bear- 

 ing upon the ac^tion spectrum of the ultraviolet in producing genetic 

 effects. It is interesting to note that wave length 2()5 m/x is about seven 

 times as effective as wave lengths 297 and 302 m^, and that the two latter 

 wave lengths are not appreciably different in effectiveness. The effective- 

 ness of wave length 254 m^t is about two-thirds that of 265 m/x though the 

 significance of this difference is perhaps questionable. The effectiveness 

 of wave length 280 mn is about half that of 265 m^. From the resem- 

 blance between these values and the absorption spectrum of nucleic acid, 

 the authors conclude that absorption by nucleic acid is of essential sig- 

 nificance in determining the genetic effects of ultraviolet radiation. 



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