BIOLOGICAL EFFECTS OF ATOMIC RADIATION 



age for many types of cells, and at different stages of the division cycle. Comparative rates 

 of chromosome damage in vitro should be compared with those of cells in vivo. Interspecific 

 comparisons, especially between man and mouse, will provide a better basis for extrapolating 

 the genetic knowledge of mutation rates obtained in mouse studies to the human species. 

 Comparative studies on identical or homologous tissues from males and females should be 

 made in order to determine whether sex differences in response to dosage exist in human beings 

 as they appear to in other species. If means of studying the mutation rates of specific human 

 loci in suitable tissue culture cells can be worked out, it may be possible to apply methods of 

 microbial genetics to the analysis of mutation rates in human tissue cells. Finally, if the 

 successful methods of culture of human testicular and ovarian tissues already achieved can 

 be utilized for the study of radiation damage to the genetic material, it is possible that a 

 direct application of the knowledge derived from somatic and interspecific studies can be 

 made to the problem of mutation in the human germ cells, at least in the oogonial and 

 spermatogonial stages. 



It is possible, and thought to be likely by many geneticists, that some malignant neo- 

 plasms may owe their origin to somatic mutations. For this reason we feel that the application 

 of genetic methods to the study of malignant neoplasms is one of the important aspects of 

 the study of mutagenic effects of radiation. 



In this connection particularly, we emphasize that present knowledge is all too limited 

 as to the effects of low levels of radiation in inducing malignant neoplasms. We cannot say 

 with any assurance whether the dose-response curve for induction of malignant diseases is 

 linear or non-linear at low levels. Regardless of whether some or all such diseases arise 

 through somatic mutation, it is urgent that more information be obtained on this point, for 

 it is just at these low levels of exposure that the practical questions of human hazards have 

 now become important. We believe that studies of this kind on experimental mammals 

 should be extended and expanded, even though they are difficult. These must be done on a 

 large scale and should include effects of accumulated internal emitters of several kinds, es- 

 pecially the radiostrontium isotopes. Perhaps mice and rats are the most suitable organisms 

 for this purpose because of their small size and the availability of many relatively homozygous 

 lines. In the latter connection, it is suggested that lines with low incidences of malignant 

 disease be included; for in lines in which the control incidences are high, small increases due 

 to low levels of added radiation will be especially difficult to detect. In attempts to argue from 

 experimental animals to man with respect to radiation-induced malignant neoplasms, it may 

 well be important also to investigate experimental mammals with life cycles much longer 

 than those of the otherwise favored small rodents. 



In all respects — incidence of malignant changes, incidence of traits known to be ge- 

 netically differentiated, as well as developmental abnormalities that are less clear genetically — 

 it would seem that emphasis should be given to investigations of human populations known to 

 be or to have been in previous generations exposed to radiations at levels that can be esti- 

 mated. These should include such studies as are now being made on survivors of A-bomb 

 exposure at Hiroshima and Nagasaki, populations living or working in areas of much higher 

 than average background level, industrial workers exposed to radiation, radiologists. X-ray 

 technicians, and persons given medical radiation for diagnosis or therapy. Obviously such 

 investigations must extend over more than one generation. Difficult and unsatisfactory as 

 this approach is — and is likely to remain, it should be pursued with great vigor, for it is to 



