434 EFFECTS OF RADIUM RADIATIONS ON AVHITE MICE 



(seven) which showed this effect is too small to prove conclusively 

 the accelerating effect of small doses of radiation on the body growth 

 of mice. But considering that similar results have been obtained by 

 radiating plants^-^ and beetles/-^ it is reasonable that the observed 

 increase in weight might be attributed, at least in part, to the effects 

 of radiation. Since this paper was first written Russ, Chambers, and 

 Scott^^ have shown that small doses of x-rays accelerate the body 

 growth of rats. In view of this additional evidence there can be little 

 doubt that the increase in weight observed in our experiments was due 

 to the radiation. 



A dose of 2.4 millicurie hours applied over the backs of the animals 

 produced no local skin effects, but it accelerated the growth of the 

 mice as in the previous case. In addition it caused permanent sterili- 

 zation of all the females. A similar result was obtained with 4.9 milli- 

 curie hours, except that the effect on the rate of growth was uncertain, 

 A dose of 6.8 milKcurie hours produced a definite but mild skin ery- 

 thema and retarded the development of lanugo hair. But since in 

 this instance the emanation was apphed over the heads of the animals, 

 the dose reaching the ovaries was not sufficient to cause sterilization, 

 as already explained. No other definite effect was noted. 



In connection with the sterilization of the females it should be noted 

 that a dose of radiation which produced no visible skin changes was 

 sufficient to cause permanent sterility. On account of the greater 

 distance of the ovaries from the source of radiation as compared with 

 that of the skin directly below the tube, and the depth of tissue which 

 the rays had to traverse to reach the ovaries, the amount of radiation 

 acting on the latter was much smaller than the amount falling on the 

 skin. The radiation emitted by the emanation tube is reduced to 

 about 50 per cent of its initial value after traversing 1 mm. of tissue. 

 Still, while the skin was not visibly affected, the mice were sterilized. 

 This shows that the ovaries are influenced very easily by radiation of 

 this type. We can estimate the amount of radiation reaching the 

 ovaries which is sufficient to cause sterility to be less than 25 per cent 

 of the amount necessary to produce \'isible skin changes in the mice. 

 It should be noted also that whenever sterility of the female mice was 



^^Russ, S., Chambers, H., and Scott, G. M., Arch. Radiol, and Elect., 1921, 

 3Kvi, 128. 



