The Germ Theory of Disease

The French Chemist Louis Pasteur found that bacteria was the cause of disease after experimenting with the fermentation process of alcohol. He learned that heat killed bacteria and he also came up with the process of pasteurization.
with Pasteur's discovery, doctors were able to make the connection that bacteria was the reason why many of their patients were during during or after surgery. This is why they began to use antibacterial cleanser to clean the surgical room.