Penicillin—the most famous and one of the most powerful infection fighters of the twentieth century—was discovered by Alexander Fleming (1881–1955) at St. Mary's Hospital in London, England, in 1928. The story goes that Fleming was cleaning out discarded glassware in the laboratory, when he noticed that a green mold seemed to be killing bacteria stored in a petri dish, the special glassware used to grow laboratory specimens. Fleming identified an agent in the green mold that became known as penicillin. It took a further ten years for Fleming's research to be taken seriously. Penicillin was at the forefront of the fight against disease throughout the late twentieth century. It controls many bacterial infections, from minor strep throats to killers such as bacterial meningitis.

Penicillin is not a wonder drug. It is useless against some common infections, including tuberculosis, and it triggers an allergic reaction in many people. Nevertheless...