1242 



BIOLOGICAL EFFECTS OF RADIATION 



Table 21 —The Effects of Equal EtreRGiES of Hard and Soft X-rays on the 

 Production of Sex-linked Lethal Mutation in Drosophila melanogaster 



Timofeeff-Ressovsky (185) 



AH of these experiments involve gross lethal-mutation rate; they are 

 subiect to the same considerations, therefore, as were earlier met with in 

 the dosage-effect experiments. Moreover, since the extraordmanly 

 powerful short waves are involved, secondary radiation confuses the 

 Issue to a considerable degree. Thus, for example, the increase m 

 mutation rate found by Medvedev (87) in flies contaming lead over 

 similarly irradiated normal flies is due to an increase m the amount of 

 secondary radiation (Stadler, 164). This is not the case with the uUra- 

 violet portion of the spectrum. Here, however, owmg to the s ight 

 ; netraUon, no certain effects were obtained (3 4, ^^.f \1^^«);^" 

 recent experiments of Altenburg (5), in which the egg itself was irradiated 

 while the germ cells were still localized in the polar cap. At this early 

 stage, cells carrying an induced lethal would form a large numb^^ °f the 

 later mature germ cells, so that the appearance of the ^--.^t^^;^^" 

 several members of a family serves as a further check of its induction by 

 the radiation. Eight such lethals were found in 108 groups of progenies 

 from treated eggs, and one (possibly an experimental error) m the 110 

 control progenfes. The further application of this method gives much 

 promise for the discovery of selective effects at different wave-lengths. 



Visible light has as far as is known no effect on mutation rates. JNe - 

 ther have effects been found with infra-red radiation (unpublished data) 

 supersonic waves (Hersh, Karrer, and Loomis, 73), or an elect-tat 

 field (Horlacher, 75; Schmitt and Oliver, 147). Hanson and Heys 67) 

 have reported somatic modifications following exposure to alpha radiation 



from polonium, but no mutations. . .„ +Uot in 



It may be surmised, from an inspection of the experiments, that, in 

 spite of the fact that the obvious things have been done to discover gross 

 differences, any selective effects on particular genes would not have been 

 found in this way. Such effects, which are the interesting and important 

 ones, remain to be investigated although, as has been previously remarked, 

 they are hardly to be expected in the spectral regions of shorter wave- 

 length than the ultra-violet. I 



