André Michel LwoffDied 30 Sep 1994 at age 92 (born 8 May 1902). French biologist who contributed to the understanding of lysogeny, in which a bacterial virus, or bacteriophage, infects bacteria and is transmitted to subsequent bacterial generations solely through the cell division of its host. The observation of isolated bacteria led him to the conclusion that lysogenic bacteria did not secrete bacteriophages, that the production of bacteriophages led to the death of the bacterium, and above all that this production must be induced by external factors. It was this hypothesis which, together with Louis Siminovitch and Niels Kjeldgaard, led Lwoff to discover the inductive action of ultraviolet irradiation (1950). His discoveries brought him (with François Jacob and Jacques Monod) the 1965 Nobel Prize for Physiology or Medicine.