born Aug. 13, 1912, Turin, Italy
died Feb. 6, 1991, Lexington, Mass., U.S.
Italian-born U.S. biologist.
He fled Italy for France in 1938, arriving in the U.S. in 1940. In 1942 he obtained an electron micrograph of phage particles that confirmed earlier descriptions of them as consisting of a round head and a thin tail. In 1943 he and Max Delbrück showed that viruses can undergo permanent changes in their hereditary material. He also proved that the simultaneous existence of phage-resistant bacteria with phage-sensitive bacteria in the same culture was a result of the selection of spontaneous bacterial mutants. In 1945 he and A.D. Hershey demonstrated the existence not only of such bacterial mutants but also of spontaneous phage mutants. The three men shared a 1969 Nobel Prize.