Childbed fever accounted for half of all maternal deaths associated with childbirth in the 1800s, but no one knew the cause or how to prevent it. Ignaz Semmelweiss, a medical student in Vienna, tried making doctors wash their hands before encountering the mother, significantly cutting the death rate. In America, Dr. Oliver Wendell Holmes had a similar idea. But it was not until Louis Pasteur's germ theory of disease that the idea of handwashing to save a patient's life became popular among phyisicans.