RADIATION AND THE STUDY OF MUTATION IN ANIMALS 1241 



When all these considerations are taken into account, the apparent 

 linear relation loses its simplicity. It would seem that a detailed deter- 

 mination of the characteristics of the curve at very low intensities is 

 necessary, and some practicable method must be found for dealing with 

 the dosage-effect function for single genes. 



THE RELATIVE EFFECTIVENESS OF DIFFERENT WAVE-LENGTHS 



It has been shown clearly that all of the short-wave radiations are 

 effective in the production of mutations. The first experiments of Muller 

 (105) with X-rays were followed by the demonstration of Hanson and 

 Heys (60) that radium emanations were effective in proportion to the 

 ionization which they produced in air (Table 20). Likewise, Serebrovsky 



Table 20. — The Relation between the Ionization Produced by Radium Emana- 

 tions AND the Percentage of Lethal Mutations in the X-chromosome of 



Drosophila melanogaster 

 Data of Hanson and Heys (60) 



and Dubinin (152) found no differences between the effect of soft and 

 hard X-rays. Later, Hanson, Heys, and Stanton (70) varied the wave- 

 length by using kilovoltages from 40 to 99, and got an approximately 

 linear relation with the ionization (Table 19, column 5) produced at 

 each voltage. It may be remarked that they did not determine the 

 identity of effect at the same ionization for different wave-lengths, a 

 weakness in their experiments which vitiates their conclusions consider- 

 ably. Later Schechtman (146) and Efroimson (43) determined the 



o 



dosage-effect relation at two different wave-lengths (1.5 and 0.2 A) and 

 found them sensibly identical (Table 19). Gowen and Gay (52) found 



o 



no significant differences between the Cu and Cr radiation (1.5 and 2.2 A, 

 respectively) (Table 19a). Timofeeff-Ressovsky (185) has found equal 

 effects at the same dosage in r-units, for different wave-lengths (Table 20). 

 Conclusive data as regards the rays of radium are not as yet avail- 

 able (185). 



