254 



H. J. CURTIS AND CATHRYN CROWLEY 



The survival curves to date are shown in Fig. 3. It will be noted that so 

 far, except for some acute mortality in the neutron-irradiated animals, there 

 has been little mortality. The weight curves show the experimental animals 

 to have essentially the same weight as the controls. 



-1 — \ — r 



1 — \ — I 1 I 



1 — I — r-i m r 



100 



_ 90 

 o 



S. 80 



^ 70 



^ 60 

 o 



£ 50 



40 



30 



20 



10 



Q- 



?^ 



■*^— *-^*r\ 



300 r fast neutrons, single dose 



7-5 r/day, chronic y-rodiation 



Control 



I I 1 LJ 



60 



100 140 180 



220 260 300 

 Age (days) 



340 380 420 460 



Fig. 3. Survival curves for the animals shown in Figs. 1 and 2. 



I I I I I I I I I I I I I I I I 



• 7-5 r/day chronic y-radiation 10 animals 

 ^ 7-5 r/day chronic y- radiation 5 animals 



o Control 10 animals 

 A Control 5 animals 



a 234 X-ray single dose 



Expected frequency of chromosome aberrations 



from chronic radiation without healing 



I I I I \ \ \ I 



220 260 300 340 380 



Age (days) 



Fig 4. Percentage of chromosome aberrations plotted as a function of age of the mice for 

 (1) control animals, (2) animals chronically irradiated at 7-5 r/day starting at 2 months of age, 

 and (3) animals which received a single dose of 234 r of X-rays at age of 2 months. The time at 

 which the chronically irradiated mice had accumulated 234 r is indicated, and the broken Una 

 is the slope one would have expected for the chronically irradiated group if there were no 

 recovery process. 



The upper curve in Fig. 4 shows the percentage of chromosome aberra- 

 tions in mice given a single dose of 234 r of X-rays at 2 months of age, 



