It was sometime in May, 1951, when George Beadle came into my laboratory at Caltech with a visitor from Zürich, a Professor Ernst Hadorn. At the time I was much immersed in the characterization of a new nucleoside accumulated by a Neurospora mutant and I was not delighted at the suggestion that I drop that for a time and assist the visitor with a project of his. He wanted to learn about the relatively new technique of paper chromatography and to make use of it for studies of Drosophila mutants. I didn't know much about Drosophila at the time but I was at once caught up in the infectious enthusiasm of this man. After an hour or so of remarkably lucid explanations and expectations I found I had agreed not only to demonstrate the technique but to participate fully in the whole program for the next few weeks. To top it off, "So---," said Professor Hadorn in a characteristic manner, "for the next three weeks you will come to work at seven in the morning, there will be no time for lunch, very little for dinner, and there will be no weekends." There was a smile when he said it but I had the feeling he meant it and in actual fact that is the way we did it. So--that same day we squashed some flies on filter paper and ran the first of many chromatograms.