"Drosophila in aseptic culture3; 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 tryptophan4, and with A.J. Haagen-Smit to identify it as kynurenine5, originally isolated by Kotake, and later structurally identified correctly by Butenandt."