On September 28, 1928, Alexander Fleming returned from holiday to his lab at St Mary’s Hospital in London and noticed that a stray mold on one of his staphylococcus plates had cleared the bacteria around it. He called the substance penicillin. It stayed a laboratory curiosity for more than a decade until wartime research turned it into a mass-produced medicine, the story told in the discovery of penicillin. This photograph, taken for the Ministry of Information about fourteen years after the discovery, shows Fleming at his bench at St Mary’s, still studying petri dishes of bacteria. Photograph D 17801 from the Imperial War Museums collection, via Wikimedia Commons, public domain (expired UK Crown copyright).