In 1860 Paris, a doctor was shot by a patients husband. He was shot out of anger because his patient died from childbed fever.
Louis Pasteur, a chemist who studied microbes, found that germs on their medical instruments are killing their patients.
Three out of 10 pregnant women died from childbed fever. People believed that the organisms were the result of the disease and not the cause but Pasteur believed it was the other way around. Pasteur pushed for doctors to wash their hands and boil their medical tools to remove germs.
This argument took him all the way to a meeting with the emperor. The emperor didn't agree with Pasteur and thought it was crazy to think that something so small could kill a human. Pasteur was ordered to conclude his research with microbes and discard all of his work.
10 years later, Pasteur no longer lives in Paris and continued his studies with microbes. The sheep around his home were infected with the black plague and Pasteur found a vaccine to gain immunity against the disease for the sheep. With this discovery, he found that some germs can remain in a dormant state until conditions are suitable for the germ.
Scientists didn't believe that his vaccine cured the sheep with the black plague. They decided to challenge Pasteur to prove him wrong about his vaccine. They injected 50 sheep with anthrax. 25 of the sheep had Pasteur's vaccine and the other 25 didn't.