In 1928, the Scottish scientist Alexander Fleming was tidying his lab. He was about to throw away an old petri dish of bacteria he’d been studying when he saw a big patch of mold on it. When Fleming looked closer, he noticed that the bacteria around the mold were no longer growing. He realized the mold was killing the bacteria. Fleming realized he might have chanced upon a weapon to fight bacteria. He set his lab team to work. After a few weeks, they identified the fungus that had killed the bacteria, and Fleming named it penicillin. He had discovered antibiotics – bacteria killers that have saved millions of lives since their discovery.