Video of a game show called 'The greatest science investigator of all time', in whcih famous scientists from history describe their life's work and explain why they deserve the title. On this show it's the turn of Sir Alexander Fleming, who describes how in 1928 he discovered penicillin which kills different bacteria responsible for serious human infections. The most important part of the discovery happened while he was away on holiday. A blob of mould had grown on a dirty dish in his lab. All around the mouldy blob, there were no bacteria growing. He reasoned something in the mould was killing the bacteria. This substance is what he later called penicillin. While this was a fortunate accident the important thing was that he noticed what others might have missed. The discovery of penicillin led to a group of medicines called antibiotics, which have saved countless lives.