One of the most famous experiments of the nineteenth century was when John Snow discovered the source of a cholera outbreak. It turns out that cholera is transmitted when human waste contaminates water that people drink. Snow found out that there was a large number of sick people in Soho in London. After talking to many people in the area and mapping where each sick person lived, he realized that the sick people were almost all getting their drinking water from the same public water pump. He solved the epidemic by having the water pump's handle removed so that the people would get water from some other place. It worked, and the epidemic was soon over.