Protective Methods in Radiology 271 



acter, any inherited qualities do not become evident unless a 

 mutated gene meets another like itself. Muller ^^ has calculated 

 the chances of the meeting of two genes originating from inde- 

 pendent mutations and has found that, on the average, at least 

 30, but more probably 100. generations would pass before a 

 recessive abnormality of a seriously harmful nature would 

 manifest itself by this process. There would thus be a "latent 

 period" of 900 to 3,000 years. Muller has also calculated the 

 chance of the meeting of two genes descended from the same 

 original mutated gene, taking into account the degree of in- 

 breeding. It is found that the latent period in this case is of the 

 order of 5,000 years. It should be mentioned that spontaneous 

 gene mutations occur naturally, and that these may be produced 

 by the effects of natural radioactivity. 



Ignoring the ionization produced by the radioelements in the 

 air, since the ions are largely due to alpha rays, which can have 

 little effect on the body, it can be shown that the remaining 

 ionization due to cosmic rays and to beta and gamma rays from 

 radioelements in the air ^ corresponds to a dosage rate of 

 2.2 X 10^ 1* per second, or to 0.0002 r per day of 24 hours, or to 

 0.07 r per year. If all spontaneous mutations are caused by 

 natural radiation — and this fact has not been established — then 

 the natural mutation rate can be said to correspond to the irradia- 

 tion of the whole human race throughout past ages at the rate of 

 0.07 r per year, that is, to doses up to 5 r during the lifetime 

 of each person. If then, from now on, only a fraction, e.g., 1%, 

 of the race is exposed to ionizing radiations, either as workers 

 or as patients, it seems logical to deduce that the natural mutation 

 rate would at the most be only doubled even if each person in 

 this minority received, on the average, 500 r in his lifetime. 



In assessing the permissible dose on which to base future 

 protection schemes, it will be necessary to know what fraction 

 of the race is to be subjected to artificial radiation and what 

 increase of the spontaneous mutation rate is justifiable, offsetting 

 the degree of race degeneration against the benefits bestowed by 

 radiation. It does appear, however, that the suggestion made 

 in an earlier paper by IMuller ^^ that the dosage rate should be 



