Practice tests that explain every answer

In 1847, a Hungarian obstetrician named Ignaz Semmelweis noticed something his colleagues had managed to overlook for years. Women who delivered their babies in the ward staffed by physicians died of puerperal fever at nearly three times the rate of women delivered by midwives in the ward next door. The two wards were otherwise alike: same building, same admission days, same patients arriving in the same condition.

Semmelweis worked through the differences one at a time. The physicians, unlike the midwives, spent their mornings performing autopsies. They then walked directly to the delivery room. Semmelweis proposed that some invisible material was being carried from the corpses to the labouring women on the physicians' hands, and he ordered his staff to scrub with a chlorinated lime solution before every examination. Mortality in the physicians' ward fell from eighteen per cent to around two per cent within a year.

His colleagues were not persuaded. Germ theory was still decades away, and Semmelweis could not say what the invisible material was — only that washing removed it. Worse, his conclusion carried an accusation: that respectable doctors had been killing their own patients. Semmelweis was dismissed from his post, and the practice lapsed after he left. He died in an asylum in 1865, the year Joseph Lister began publishing on antisepsis.