Penicillin was the first antibiotic agent successfully used to treat bacterial infections in humans. Penicillin’s effect on bacteria was first observed by biologist Alexander Fleming in 1928, but it was not until 1941 that scientists purified the substance and established that it was both effective in fighting infectious organisms and not toxic to humans. The first successful treatment occurred the next year. Where did scientists find the mold that allowed them to mass produce the drug? Discuss