While penicillin is widely cited as one of the most important discoveries of the 20th century, uncertainty over whether or not Alexander Fleming actually discovered it caused many to question his 1945 Nobel Prize for Medicine. Critics questioned the novelty of Fleming's find, referencing studies dating back to the 1870s that note the bacteria-fighting properties of the mold Penicillium notatum. Even Fleming himself admitted the discovery was a complete accident and conceded that the first known reference to penicillin was actually from Psalm 51: "Purge me with hyssop and I shall be clean." In the end though, he was indeed the first person to isolate and produce penicillin, which has since saved millions of lives worldwide, so he is worthy of high praise.