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A decade later a team at Oxford took up the problem and produced enough penicillin to test on patients.

In 1928 Alexander Fleming returned from holiday to find that a stray mould had contaminated one of his bacterial cultures.

By the end of the Second World War the drug was being manufactured on an industrial scale.

Around the colony of mould, the bacteria had been destroyed, leaving a clear ring in the dish.

Fleming published his observation but was unable to purify the active substance in useful quantities.