George Wald

From the Nobel Foundation:

On receiving the Ph. D. he was awarded a National Research Council Fellowship in Biology (1932-1934). This was begun in the laboratory of Otto Warburg in Berlin-Dahlem and it was there that Dr.Wald first identified vitamin A in the retina. Vitamin A had just been isolated in the laboratory of Professor Paul Karrer in Zurich, and Dr. Wald went to Karrer's laboratory to complete the identification. That done, he spent a period in the laboratory of Otto Meyerhof, at the Kaiser Wilhelm Institute in Heidelberg. The second year of the fellowship was spent in the laboratories of the Department of Physiology at the University of Chicago.

"George Wald: Biographical," Nobel Foundation (1967)

Nobel Laureate, Prize in Physiology or Medicine, 1967