Fleming was awarded a share of the 1945 Nobel Prize in physiology and medicine for his discovery of penicillin. In 1928, Fleming noticed that a mold, which had apparently come through a window of his laboratory, had contaminated a culture plate on which he was growing bacteria. Around the mold was a clear circle, where all the bacteria had been killed. Fleming identified the mold as Penicillium notatum and called the bacteria-killing substance it produced penicillin. Fleming later found that penicillin kills many kinds of bacteria and is nonpoisonous to humans. Fleming also discovered lysozyme, a substance in the body that can dissolve certain bacteria.
