Fleming, Sir Alexander, 1881-1955, Scottish bacteriologist, discoverer of penicillin (1928) and lysozyme (1922), an antibacterial substance found in saliva and other body secretions. Educated at St. Mary's Hospital Medical School, Univ. of London, where he later became professor of bacteriology, he published many articles on bacteriology, immunology, and chemotherapy. He shared the 1945 Nobel Prize in Physiology or Medicine with Ernst B. Chain and Sir Howard W. Florey for work on penicillin. Fleming was knighted in 1944.