If early American settlers had sores or infected blisters, they covered them with a piece of moldy rye bread. And moldy cornbread was used to help cure the sores from measles. But in the late 1800s and early 1900s, scientists and doctors discouraged people from using this “old time” cure. Fleming immediately went to work growing more of the mold in a pure culture. In experiments, he learned that the “mold juice,” as he called it, could kill the bacteria that cause scarlet fever, pneumonia, meningitis, and diphtheria. It was an amazing discovery. With the success of penicillin, scientists began researching other molds, plants, and natural substances to see what else might contain antibacterial properties. Unfortunately, doctors did not understand that by using the antibiotics too much, bacteria would develop strains that are resistant to the antibiotics.