He did research on the influenza virus at the Univ. of Michigan, in 1946 became assistant professor of epidemiology there, and in 1947 went to the Univ. of Pittsburgh. In 1963 he became director of the Salk Institute for Biological Studies at the Univ. of California, San Diego. He is known for his work in developing a vaccine against poliomyelitis. The Salk vaccine is made by cultivating three strains of the virus separately in monkey tissue. The virus is separated from the tissue, stored for a week, and killed with formaldehyde; tests are then made to make certain that it is dead. A series of three or four injections with the killed virus vaccine is required to confer immunity.