universality of need for the B vitamins, and the enzymatic basis of this require- 

 ment, had been clearly defined. The vision of Lwoff and Knight had already 

 indicated a correlation of the need of microorganisms for "growth-factors" 

 with failure of synthesis, and correlated this failure with evolution, particularly 

 in relation to the complex environment of "fastidious" pathogenic micro- 

 organisms. However, the tendency at this time was to consider "growth- 

 factors" as highly individual requirements, peculiar to particular strains or 

 species of microorganisms as isolated from nature, and their variation in these 

 respects was not generally considered as related to gene mutation and varia- 

 tion in higher organisms. Actually my ignorance of and naivete in genetics 

 was probably typical of that of most biochemists and microbiologists of the 

 time, with my only contact with genetic concepts being a course primarily 

 on vertebrate evolution. 



After completing .graduate work at Wisconsin I was fortunate in being able 

 to spend a year studying at the University of Utrecht with F. Kogl, the dis- 

 coverer of the growth factor biotin, and to work in the same laboratory with 

 Nils Fries, who already had contributed significantly in the field of nutrition 

 and growth of fungi. 



At this time. Professor Beadle was just moving to Stanford University, 

 and invited me as a biochemist to join him in the further study of the eye- 

 color hormones of Drosophila, which he and Ephrussi in their work at the 

 California Institute of Technology and at Paris had so briUiantly established 

 as diffusible products of gene-controlled reactions. During this, my first con- 

 tacts with modem genetic concepts, as a consequence of a number of factors 

 — the observation of Khouvine, Ephrussi and Chevais (2) in Paris that 

 dietary tryptophane was concerned with Drosophila eye-color hormone pro- 

 duction; our studies on the nutrition of Drosophila in aseptic culture (3); and 

 the chance contamination of one of our cultures of Drosophila with a particular 

 bacterium — we were able to isolate the v+ hormone in crystalline state from 

 a bacterial culture supplied with tryptophane (4), and with A. J. Haagen- 

 Smit to identify it as kynurenine (5); originally isolated by Kotake, and later 

 structurally identified correctly by Butenandt. It might be pointed out here 

 that kynurenine has since been recognized to occupy a central position in 

 tryptophane metabolism in many organisms aside from insects, including 

 mammals and fungi. 



At about this time, as the result of many discussions and considerations of 

 the general biological applicabihty of chemical genetic concepts, stimulated 

 by the wealth of potentialities among the microorganisms and their variation 



S-41 



