Penicillin: medicine's greatest discovery. The super-substance became the world's first antibiotic and made many lethal bacterial infections a thing of the past. The man credited with its discovery is Alexander Fleming, who received the Nobel prize (among numerous other honors and distinctions) for his work. What started as an accident--spores floating in through an open window-- turned into a revolution, completely changing the nature of medicine. Incredible. But is that really what happened?