Sir Alexander Fleming (6 August 188111 March 1955) was a Scottish biologist, pharmacologist and botanist. His best-known discoveries are the enzyme lysozyme in 1923 and the antibiotic substance benzylpenicillin (Penicillin G) from the mould Penicillium notatum in 1928, for which he shared the Nobel Prize in Physiology or Medicine in 1945 with Howard Florey and Ernst Boris Chain. He wrote many articles on bacteriology, immunology, and chemotherapy.