In the 18th century, smallpox ravaged Europe. In China, healthy people were exposed to a sick person's clothing and after a small fever, these people were unaffected by epidemic. In Turkey, smallpox pus was put into small cuts on a patient's arms and the results were just as effective. This process was called inoculation. In 1776, Edward Jenner was inoculating his patients in the countryside and noticed that people who had the Vaccinia virus, which they would have gotten from milking cows, were immune to smallpox. While studying chicken cholera, Louis Pasteur and Emile Roux cultivated cholera microbes in chicken broth and then let it age to weaken the microbes. When chickens were injected with the weaker version of the disease, they became immune to full strength cholera microbes. In 1880, Pasteur revealed this vaccination theory and went on to finalize a rabies vaccine using the same method. Paul Ehrlich's work on the immune system helped us understand exactly how vaccines work; when a weak version of a disease is injected into the body, the body learns to fight it which helps it resist the stronger disease.