Penicillin: Discovery of Antibiotics (Fleming, 1928)

In September 1928, Alexander Fleming returned from vacation to find that a mold (Penicillium notatum) had contaminated a Petri dish of Staphylococcus bacteria — and that a clear ring surrounding the mold was free of bacteria. He identified the mold's secretion as penicillin and published his findings in 1929, but it took Howard Florey and Ernst Chain at Oxford to develop it into a medicine by 1941. Mass production for Allied forces began in 1943; by D-Day, enough penicillin existed to treat every major infection among Allied troops. Before antibiotics, a scratch could be fatal; bacterial infections killed more soldiers than combat in every war before World War II. Penicillin alone is estimated to have saved over 200 million lives.