THE MUTATED GENE 45 



exercises the same effect. Zeleny (1923) who first analyzed such 

 cases, as reported, summarized the results with the words: 

 "... demonstration ... of the fact that the gene Ultrabar 

 has the same type of reaction as a temperature difference. It is 

 possible to state the effectiveness of particular germinal factors 

 in terms of corresponding effects of temperature." Rates of 

 reaction were not mentioned in this connection, as Goldschmidt 

 had already done in 19206 in trying to explain the phenocopic 

 phenomenon (as well as the general action of genes), but no other 

 way seems available to describe these temperature effects and 

 simultaneously the effect of the mutant alleles. Such was done 

 by Goldschmidt (1927c) in regard to the facts found by Zeleny; 

 and in his last reference to his work, Zeleny (1933) himself writes: 



Since the circumstances connected with the production of the Bar 

 mutants make it possible to formulate a theory of difference between 

 the genes of the series in terms of structural change, quantitative in 

 some cases, and since the resulting somatic effects may be measured in 

 terms of temperature effect upon an individual with unchanged genes, 

 it seems worth while to postulate, for purposes of experimental test, 

 theories of gene action in terms of relative rates of the physiological 

 effects they produce. 



The second type of experiments did not use external agencies 

 within the range of physiological conditions but actual shocks, 

 which proved fatal if prolonged. It is characteristic for this 

 set of experiments that similar effects are produced by different 

 methods. Thus heat, frost, X rays, narcotics, C0 2 (the latter 

 in von Linden's experiments on butterflies) produced similar 

 effects. True, they were not entirely identical. Thus Friesen's 

 X-ray phenocopies in Drosophila were not wholly — though in 

 part — identical with those produced by heat; in the experiments 

 of Kuehn and his pupils, heat and frost had somewhat different 

 effects on certain parts of the wing pattern of the flour moth. 

 But in a general way, the same effect was produced. From 

 such facts, the early experimenters upon the butterfly wing, 

 who were not yet interested in genetical problems, concluded 

 that the effect was produced by reducing differentially the 

 velocity of some of the processes involved in the production of 

 the normal phenotype (von Linden, 1904). Goldschmidt (19206) 

 when analyzing the typical effects of temperature upon the 

 lopidopteran wing went a stop further: He stated that evidently 



