416 RADIATION BIOLOGY 



damaging action on more rapidly growing tissues. This has in fact 

 proved to be the case. It now forms the basis for the use of mustard as 

 an alternative or accessory to radiation in the treatment of malignancies. 

 This is one way in which radiation genetics, this time through its offshoot, 

 mustard mutagenesis, has had an important impact on therapy. 



Closely following upon, and in part independently of, the work on 

 mustards, an ever increasing series of chemicals has been found to have 

 markedly mutagenic properties in given organisms, although few if any 

 others are as potent, in doses which it is practicable to apply, as are the 

 mustards themselves, and few others have yet been shown to be muta- 

 genic in organisms in general. For some alleged mutagens, especially for 

 some of the numerous substances reported to be mutagenic by Rapoport 

 (1946a, b, 1948a, b) on the basis of independent work carried out by him 

 in the U.S.S.R., confirmation is still lacking, but for other substances 

 reported by him, as well as for a number of quite different substances, 

 there is now no room for doubt, at least in certain organisms. 



A notable, and probably the first, example found, following the mus- 

 tards, of a substance that is probably mutagenic for organisms in general, 

 is the narcotic ethyl urethane. It was discovered by Oehlkers (1943) that 

 this substance produces chromosome changes in higher plant material, 

 and it was discovered both by Rapoport (1946b) and by Vogt (1948, 1950) 

 that it produces lethals, apparently of the gene-mutation kind, in Dro- 

 sophila, and by Vogt that it also produces chromosome changes in 

 Drosophila. In Rapoport's work, urethane was only one (although the 

 most effective) of several carbamates found to produce mutations, and he 

 appears to regard mutagenicity as characteristic of this entire group of 

 substances. 



In recent years the noteworthy fact has emerged that virtually all 

 agents which have thus far been found to produce gene mutations, and 

 for which the matter has been satisfactorily investigated, have also been 

 found to have some effect in producing structural changes of chromo- 

 somes. This finding has recently been extended to a mutator gene in 

 Drosophila by Hinton, Ives, and Evans (1952). 



For a recent list of these chemicals the reader may be referred to Jensen, 

 Kirk, Kolmark, and Westergaard (1952) and, for important additional 

 substances, investigated by her, to Bird (1950, 1951, 1952). A bibliog- 

 raphy of the extensive Drosophila literature on the genetic effects of 

 chemicals has been published by Herskowitz (1951). An attempt to list 

 chemical mutagens here would entail too great a digression, in view of the 

 state of flux of this subject and the fact that, although many of them do 

 fall into certain groups, these groups have not yet been found to show 

 any agreement with one another in regard to features of either their struc- 

 ture or their mode of chemical or physiological action. Thus there is as 

 yet no unified or agreed upon chemical interpretation of their mutagenesis, 



