GREAT SCOT! ALEXANDER FLEMING, DISCOVERER OF PENICILLIN, WAS BORN ON THIS DAY IN 1881: The story is that just after returning to his laboratory after a month-long vacation, he saw that one of his staphylococcus-containing petri dishes had gotten moldy. Upon closer inspection, lo and behold, he saw the area adjacent to the mold was bacteria free.

Fleming was modest about his discovery, saying that sometimes one finds what one is not looking for. But it would be wrong to believe that the good doctor was just a lucky guy who happened to run across the moldy bread that revolutionized medical science—à la Jed Clampett discovering oil on the Beverly Hillbillies. Fleming already had a reputation as dogged and meticulous researcher (if occasionally an untidy one). And he was looking for a method to eradicate harmful staphylococcus. When he looked at that petri dish, he had a fighting chance of recognizing what he was looking at. The rest of us … not so much.