In 1940, Howard Florey, Ernst Chain and others in England discover how to purify and preserve penicillin. The initial strains, which came from a moldy melon in Peoria, are submitted to X-ray radiation and ultraviolet light to produce more potent mutant strains.

In June 1941, Florey and Norman  Heatley traveled to the United States. Concerned about the security of taking a culture of the precious Penicillium mold in a vial that could be stolen, Heatley suggested that they smear their coats with the Penicillium strain for safety on their journey. They eventually arrived in Peoria, Illinois, to meet with Charles Thom, the principal mycologist of the US Department of Agriculture, and Andrew Jackson Moyer, director of the department’s Northern Research Laboratory. Thom corrected the identification of Fleming’s mold to P. notatum; it was initially identified as P. rubrum