1244 



BIOLOGICAL EFFECTS OF RADIATION 



are irradiated, and then kept from mating for long periods, produce as 

 many mutations as they would have, if they had mated immediately. 

 Were there a "back-reaction," fewer mutations would be expected from 

 the sperm which were kept for a long time after irradiation. 



Table 24. — The Effect on Lethal-mutation Rate in Drosophila melano- 



GASTER of Aging Sperm after X-ray Treatment 



Muller (105); Harris (72) 



A. cf cf treated with X-rays, mated to virgin females, transferred to new culture 



bottles after six days (Muller) 



B. d^ cf treated with X-rays, isolated from females until final mating (Harris) 



Similar conclusions follow from the experiments of Timof^efif-Res- 

 sovsky (185; Table 22), Patterson (134; Table 25), and Serebrovsky and 

 Dubinin (152). These workers have been interested in a comparison of 

 the effects produced by a given amount of energy given in one dose, or 

 split up into several. From the foregoing data, identical effects would be 

 expected in the two sets of experiments; and indeed such is the case. 

 Some caution is perhaps still necessary in accepting the conclusions com- 

 pletely; the detection of a difference, assuming one were present, depends 

 upon the relation between the rates of the reactions concerned. Inspec- 

 tion of the tables makes it clear that the existing data are not sufficient to 

 test the point thoroughly, a difficult problem indeed, and one which 

 hardly seems profitable in view of the negative results of the experiments 

 on the aging of treated sperm. 



INDUCED CHANGES OF SUSCEPTIBILITY TO IRRADIATION 



From the foregoing it would seem that the secondary processes, if they 

 exist, are not easily approachable. The radiochemical process may, 

 however, be studied by the analysis of the effect of environmental 

 changes during radiation. 



It has already been remarked that were simple radiochemical processes 

 involved, the temperature coefficient of induced mutation rate should 



