Sir Alexander Fleming on this day in 1929 left a plate of staphylococcus bacteria uncovered, and he noticed that a mold that had fallen on the culture had killed many of the bacteria. He identified the mold as penicillium notatum, similar to the kind found on bread. Fleming introduced his mold by-product called penicillin to cure bacterial infections which was undoubtedly one of the greatest developments in health and medicine.