390 RADIATION BIOLOGY 



observed proved to be gross chromosomal aberrations, and it remained 

 possible to apply this interpretation even to those changes which were 

 inherited in a more or less Mendelian manner. 



Although the works mentioned were the first to give definite evidence 

 of the abundant production by radiation of point mutations and struc- 

 tural chromosome changes that were transmitted to subsequent genera- 

 tions, they had of course been led up to by a long succession of experi- 

 ments on the effects of ionizing radiation on the hereditary material. 

 Thus the production of abnormal and moribund embryos from irradiated 

 sperm in amphibia, mammals, fish, and echinoderms, reported in the 

 years 1907 to 1913 (see Chap. 8, Sect. 14), had been generally regarded by 

 those conducting the experiments as evidence of damage to genetic 

 material in the chromosomes. It was, however, much longer before clear- 

 cut results capable of genetic interpretation could be obtained. 



It is true that certain suggestive results were reported. Among these 

 were alterations in the manner of growth and nutritional requirements of 

 mold colonies, produced by radiation in work of Dauphin (1904) ; somatic 

 abnormalities, not transmitted to the next generation, which were found 

 by Gager (1908a, b) in Oenothera derived from germ cells treated with 

 radium; and two peculiar variations. Beaded and Truncate wings, of 

 unclear mode of inheritance, found by Morgan (1911) in descendants of 

 radium-treated Drosophila. Loeb and Bancroft (1911) also reported 

 finding some mutations in Drosophila after radium treatment, but their 

 manner of appearance, in both treated and control lots, led other Dro- 

 sophila workers to infer that the genes concerned had been present 

 heterozygously in the original stocks. Similar doubts seemed justified in 

 the case of the mutations found by Guyenot (1914) after ultraviolet treat- 

 ment of Drosophila. On the other hand, in a number of experiments on 

 other material, negative results of radiation treatments on the character- 

 istics of later generations were reported, but these could not be regarded 

 as definitive either. 



The attack had been renewed in the third decade of this century. 

 For example, Unterberger (1922) reported obtaining butterflies of a size 

 which diminished from generation to generation among the descendants 

 of irradiated but not among those of nonirradiated individuals, yet results 

 of this kind (which have not been obtained by others) appear, on genetic 

 grounds, to be very dubious. Again, Little and Bagg (1923), on inbreed- 

 ing descendants of mice which had been irradiated, did find four 

 undoubted mutations of different kinds, but their controls, which were 

 only half as numerous, showed two mutations, one of them identical 

 with one of those in the treated series. (In the light of present knowl- 

 edge, the dose used by them was so small that no statistically perceptible 

 genetic effects would be expected from it.) Nadson and Philippov 

 (1925), on the other hand, certainly obtained inherited abnormalities 



