248 Action of the Genetic Material 



stood the test of time. The genie material must catalyze chains of 

 reaction which in the end produce the active substances that control 

 morphogenesis. Since the best-known active substances of this kind 

 were the hormones, I extended the meaning of this term to include 

 every substance which plays an active role in embryonic determina- 

 tion. The reason for such terminology is obvious. There is no type of 

 morphogenetic (also physiogenetic) process known which cannot be 

 controlled in some cases by genuine hormone action. The phenotypic 

 difiFerences which can be induced by sex hormones, pituitary and 

 thyroid hormones, molting hormones, and auxins in plants include all 

 known types of differentiation, which may be qualitatively as differ- 

 ent as any known or imaginable genetic difference. This suggests that 

 the interrelations of these known active substances with the cellular 

 substrate, as developed under control of the rest of the genotype, are 

 of the same basic type as all the more simple and specialized actions 

 of the end products of genically controlled reactions, which thus, in 

 a wider sense, may also be termed hormones (which, in this case, 

 includes specific enzymes). 



In Germany, later, the term Genwirkstoffe was introduced (by 

 Kiihn) to characterize chemically identifiable products of genie action 

 endowed with the capability of controlling chemical or morphological 

 developmental processes. The term has led to much confusion as well 

 as to unjustified beliefs in certain desired but not accomplished in- 

 sights. Genwirkstofe could be interpreted in two ways. First, it might 

 mean identifiable substances produced by the work (wirken) of genes. 

 If this were meant, the term would be superfluous, since it would 

 include all the long known Mendelizing differences of a chemical 

 nature like plant pigments, chlorophylls, and oxidases. The other 

 meaning of the term, the one which was given it generally, is that of 

 active substances which are gene products and control developmental 

 features. Clearly, hormones produced by genie action, also inductors 

 and morphogenetic substances, would be included in the term. But 

 when one of the substances needed for production of eye pigment 

 and absent in certain mutants was isolated by Kiihn and Caspari and 

 found to be kynurenine by Butenandt, this was hailed as the chemical 

 isolation of a Genwirkstoff. In the same way Beadle and Ephrussi, 

 who independently made the same discoveries, called the substance a 

 hormone. Long before the chemical nature was known (by Beadle and 

 Tatum's work) I warned (on the basis of the known facts of genetic 

 and chemical control of melanin ) that probably these " Genwirkstoff e" 



