1238 



BIOLOGICAL EFFECTS OF RADIATION 



ing for the energy of the quantum absorbed to produce ionization. 

 When, however, longer wave-lengths are used where selective absorptions 

 may be expected, differences may be found. Furthermore, since radio- 

 chemical reactions usually have a temperature coefficient of 1, it should 

 be found that there is no effect of temperature during irradiation. Any 

 departure from these expectations indicates the presence of secondary 

 reactions. These can, moreover, be studied by consideration of the time 

 factor in exposure which evaluates the relative rates of the different 

 reactions concerned; or by the consideration of the duration of the effect 

 after successive cell generations. 



THE RELATION BETWEEN INTENSITY AND MUTATIONAL EFFECT 



The relation between dosage and effect is one of the most extensively 

 studied of the problems attendant on the production of mutations by 

 X-rays, involving as it does simultaneously an important practical and 

 theoretical problem. In his earliest work, Muller (105) noted that the 

 higher the dosage, the greater the mutational effect. Subsequently, the 

 problem was studied in detail by various workers (cf. 22, 43, 52, 60, 70, 

 124, 125, 146, 152, 153, 185). Their data are given in Tables 19 and 

 19a, and in Fig. 6. 



Within the range studied, the relationship is roughly linear for the 

 whole group of data; in most of the individual cases, the fit to a straight 

 line is quite good. At the upper dosages, a slight falling off occurs in 

 some cases owing to undetected double lethals (cf. Timof^eff-Ressovsky, 

 185). Gowen and Gay (52) have plotted their data in the inverse fashion, 

 considering the number of chromosomes which do not have lethals, a 

 procedure which avoids this difficulty. They find an excellent fit to the 

 exponential function which follows from this treatment of the data. 



Table 19a. — The Relation between X-ray Dosage and the Percentage op 



Lethal Mutation 

 K radiation of Cu and Cr, 34 kv., 4 ma. (Gowen and Gay, 52) 



Dosage, r-units 



4,460 

 8,920 

 13,380 

 17,840 

 22,300 

 26,760 

 31,220 



Copper, 1.537 A 



4.3 + .6 



8.9 ± 1.3 



11.7 ± 1.5 



20 . ± 2.1 



29.2 ± 3.8 

 35.0 ± 5.1 



Chromium, 2.285 A 



6.8 + 1.0 



12.4 + 1.1 

 19.3 + 1.7 



26.5 ± 3.6 

 18.8 ± 2.9 

 31.8 ± 6.7 

 34.8 ± 6.7 



The experiments of the different workers agree, on the whole, when 

 the errors involved are considered. The data of Oliver and of Timof^eff- 

 Ressovsky agree most closely. Efroimson (43) and Schechtman's (146) 



