GENETICS: THE HERITABLE TRANSMISSION OF CATALYSTS 171 



tions, may here be replaced by the laws of the action of single particu- 

 late units. And the formation of a new catalyst area can change the 

 whole course of chemical events. 



The experimental facts indicate that gene K and kappa cooperate 

 in forming catalyst areas capable of synthesizing both kappa and 

 paramecin, and that this heritable result is not exclusively genie. 



Results of experiments on the chemical production of mutations, 

 begun in 1940 at the University of Edinburgh, have recently been 

 released. 11 Mustard gas, the diethyldichlor sulfide used in World 

 War I, produces heritable changes in Drosopliila and Tradescantia by 

 causing chromosome breaks and rearrangements, and genie changes, 

 in some respects like those produced by x-rays. 12 



Treatment with mustard gas produces a much larger percentage 

 of sex-linked lethals than does x-ray treatment, and also a much 

 larger percentage of "mosaics" among the mutated individuals. In 

 one striking case "a son of a mustard-gas-treated male was, both in 

 the gonads and in the soma, a mosaic for two different mutations of 

 the same gene, although it must be assumed that in the treated 

 spermatozoon each treated gene was present only once. An explana- 

 tion which seems particularly satisfactory in accounting for all these 

 observations is that the gene affected does not always mutate at once, 

 but may acquire a tendency to mutate which remains latent until a 

 later cell division. Support for this hypothesis was obtained when it 

 was found in several cases that the offspring of gonadic mosaics for a 

 mutation again were gonadic mosaics for the same mutation. In 

 these cases an induced specific instability seems to have been trans- 

 mitted from one generation to the next before giving rise to a stable 

 change. No parallel observations have been reported in literature 

 on radiation genics; but it seems worth noting that so-called unstable 

 genes, i.e., genes which tend to mutate repeatedly in the same direc- 

 tion, have been found several times in untreated material. Says 

 D. E. Lea, 13 ". . . it is tempting to consider the possibility that one of 

 the means by which evolution adapts mutability to environmental 

 requirement is the achievement of a balance between the production 

 of mutagens and sensitivity to them." 



While this experimental evidence of cytoplasmic inheritance 

 does not mean that any and all nongenic changes are necessarily 

 heritable, it demonstrates the principle and compels us to regard it 

 — to use a legal analogy — as permissive, though not mandatory 

 in function. 



In his book "Hormones and Heredity" (London, 1921) J. A. 

 Cunningham suggested that the mechanism whereby "modifica- 

 tions produced in the soma by external stimuli could affect the 



