The Journal of Heredity 



to digress upon here, but it is to be noted 

 that it has been the analyses based in 

 the first place on genetic and cytogenetic 

 studies of the reproductive cells, as 

 shown by subsequent generations, which 

 are thus helping to clear the way for 

 an understanding of the mechanism 

 by which radiation acts in inhibiting 

 growth, in causing sterilization, in pro- 

 ducing necrosis and burns, in causing 

 recession of malignant tissue, and per- 

 haps also, on occasion at least, in induc- 

 ing the initiation of such tissue. 



During the war years, a curious con- 

 firmation of the correctness of the above 

 inference regarding the nature of the 

 somatic effects of irradiation has come 

 to light. While working with mustard 

 gas in Edinburgh, J. H. Robson was 

 struck with the remarkable similarity be- 

 tween the somatic effects of this agent 

 and those produced by X-ray and radi- 

 um irradiation. This led him to wonder 

 whether perhaps mustard gas might pro- 

 duce genetic changes of essentially the 

 same kind as those known to be brought 

 about by irradiation. Comprehensive ex- 

 periments were thereupon undertaken 

 by C. Auerbach, working in collabora- 

 tion with Robson, and (as mentioned 

 on p. 263) she succeeded in showinqj 

 that in fact this substance does produce 

 mutations, both in the individual genes 

 and by breakage and rearrangement of 

 chromosome parts, such as X-rays and 

 radium do, and in similar abundance. 

 Other substances of the same general 

 group were then found to have a similar 

 effect. This constitutes the first decided 

 break in the chemical attack on muta- 

 tion. The fact that these findings were 

 made as a direct result of the above in- 

 ference, when so many previous at- 

 tempts to produce mutations by chemi- 

 cal means had failed, appears to provide 

 strong evidence that these peculiar so- 

 matic effects are in truth consequences 

 of the more underlving ones which, when 

 occurring in the germ cells, are analvzed 

 bv the geneticist in his breeding tests. 



There are, however, some very interest- 

 ing differences between the nature of the 

 genetic effects of irradiation and of these 

 chemicals, which we cannot go into here, 

 but which give promise of allowing an 

 extension of the genetic and somatic 

 analyses. 



We see then that production of muta- 

 tions by radiation is a method, capable 

 of being turned in various directions, 

 both for the analysis of the germ plasm 

 itself, and of the organism which is in a 

 sense an outgrowth of that germ plasm. 

 It is to be hoped that it may also, in 

 certain fields, prove of increasing prac- 

 tical use in plant and animal improve- 

 ment, in the service of man. So far as 

 direct practical application in man him- 

 self is concerned, however, we are as 

 yet a long way from practicing any in- 

 tentional selection over our own germ 

 plasm, although like most species we 

 are already encumbered by countless un- 

 desirable mutations, from which no in- 

 dividual is immune. In this situation we 

 can, however, draw the practical lesson, 

 from the fact of the great majority of 

 mutations being undesirable, that their 

 further random production in ourselves 

 should so far as possible be rigorously 

 avoided. As we can infer with certainty 

 from experiments on lower organisms 

 that all high-energy radiation must pro- 

 duce such mutations in man, it becomes 

 an obligation for radiologists — though 

 one far too little observed as yet in most 

 countries — to insist that the simple pre- 

 cautions are taken which are necessary 

 for shielding the gonads, whenever peo- 

 nle are exposed to such radiation, either 

 in industry or in medical practice. And, 

 with the coming increasing use of atomic 

 energy, even for peacetime purposes, the 

 problem will become very important of 

 insuring that the human germ plasm — 

 the all-important material of which we 

 are the temporarv custodians — is effec- 

 tively protected from this additional and 

 Dotent source of permanent contamina- 

 tion. 



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