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In 1847, at a hospital in Vienna, the doctor Ignaz Semmelweis noticed something terrible: on the ward attended by doctors, far more mothers were dying of fever after childbirth than on the one attended by midwives.
The doctors often arrived straight from performing autopsies, without washing. Semmelweis made them disinfect their hands with a chlorinated solution, and the deaths plummeted. He had stumbled, without yet knowing why, on the importance of hygiene long before microbes were known.
Instead of applauding him, much of the profession took offense and rejected him. Semmelweis ended his days shut away in an asylum. Years later, science proved him right: washing your hands would become one of the measures that has saved the most lives in history.
Source: U.S. National Library of Medicine