Alexander Fleming noticed a mold killing bacteria and published in 1929, but turning penicillin into a usable drug was the work of Howard Florey, a bootmaker’s son born in an Adelaide suburb in 1898. This episode follows Florey from a family crisis that left him reliant on a state scholarship, through his refusal to start his Rhodes Scholarship at Oxford until he had finished his medical exams, to the chair of pathology at Oxford’s Sir William Dunn School in 1935. There he built a multidisciplinary team, including the biochemist Ernst Chain, a refugee from Nazi Germany, and the engineer Norman Heatley, and won a Rockefeller Foundation grant of $5,000 a year for five years.

Florey later admitted that suffering humanity never crossed their minds at the start. In May 1940, four mice given streptococcus and penicillin survived while four untreated mice died. In February 1941 the police constable Albert Alexander improved within a day, but the supply ran out and he died. Florey and Heatley then took the work to a Department of Agriculture lab in Peoria, Illinois, where deep aerated vats and corn steep liquor made mass production possible.

• Penicillin grown in hospital bedpans and bottles, tended by a team of six women and filtered through parachute silk
• Heatley’s reverse extraction, shifting penicillin between water and amyl acetate by changing acidity, followed by freeze drying
• Penicillin recovered from Albert Alexander’s urine and injected back into him
• Florey left for America without telling Chain until the morning they departed, starting a lifelong rift
• He refused to patent the process, and British firms later paid royalties on American methods