1210 BIOLOGICAL EFFECTS OF RADIATION 



form? The second concerns its radiochemistry : how does short-wave 

 radiation produce mutations? It may be remarked immediately that the 

 significant advances to date have been made in the first field, an occur- 

 rence by no means surprising. 



The change in outlook brought about by the introduction of X-rays 

 into the study of mutation deserves some comment. It does not so much 

 involve fundamental concepts; those already adumbrated in the studies of 

 spontaneous mutation have proved surprisingly adequate. Now, 

 however, with the help of short-wave radiation, experiments can be car- 

 ried out that formerly would have been considered impossible. 



THE DISCOVERY OF THE EFFECT 



The history of the experiments on the genetic effects of radiation has 

 an interest of its own. In the days following the rediscovery of mendelism, 

 there were frequent attempts to induce mutations experimentally, just 

 as the control of sex was sought by various environmental agents. It was 

 evident at the time, from the cytological studies of the effects of X-rays 

 and radium on tissues, that heritable variations might be produced. 

 Attempts were not lacking to put this idea to the test. 



Among the earliest mutations found in Drosophila (Morgan, 89) were 

 some that appeared in progenies from radium treated individuals. Later 

 Loeb and Bancroft (85) claimed to have obtained positive results which 

 were shown by Morgan (91) to be unconvincing. Repetitions of such 

 experiments by Morgan (Morgan, Bridges, and Sturtevant, 93) gave 

 negative results, and Mavor (86, page 362) in his experiments on non- 

 disjunction and crossing-over changes induced by X-rays, found no 

 evidence of the production of mutations. Later, Muller and Dippel (118) 

 reported incidentally an unsuccessful experiment designed to detect losses 

 of small fragments of chromosome. 



The results on other organisms were no more convincing. Little and 

 Bagg (84) described experiments with mice in which they obtained from 

 12 treated individuals two mutations, one of which appeared in the 

 controls. Subsequent attempts (Bagg, MacDowell, and Lord, 8; 

 Snyder, 163) at repetition yielded negative results. The experiments of 

 Dobrovolskaia-Zavadskaia (24, 25) are likewise not clear, since they 

 involved one mutation probably present in the treated animal, and one 

 other, in a progeny of some 3000 mice. 



In the meantime Muller and Altenburg (114, 115), and especially 

 Muller (97 to 103, 107, 108) had carried out an extended study of spon- 

 taneous mutation in Drosophila melanogaster. As a result of his studies, 

 Muller developed a technique for the quantitative study of mutation. 

 Using this technique, and the information on X-ray dosage available as a 

 result of the previous failures, he repeated the attempt with, at la.st, great 

 succe.ss. Once the proper experiment was performed, effects of such an 



