In the 1840s Ignaz Semmelweis noticed that women died of childbed fever far more often in the doctors' ward than in the midwives' ward. The doctors came from the autopsy room. He ordered handwashing in chlorine solution. Deaths fell. Colleagues were insulted by the implication, and the practice spread slowly. The evidence arrived before the welcome.
Worth knowing
Handwashing cut deaths before the profession was ready to believe why.