In 1860, an angered husband killed his wife's doctor after she died of child bed fever. This occurred because the doctor did not wash his hands and sterilize his instruments before delivering the child. A chemist named Louis Pasteur has been publishing about sanitation and the steps doctors should take before handling a patient.
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Louis Pasteur's ideas on sanitation has led to murder and he was looked down upon by the Emperor so, he moves to Arbois, France. Sheep are dying from anthrax all over, but Pasteur makes a vaccine for the sick sheep. The medical board opposes his idea and believes that Arbois is free from anthrax. Pasteur is convinced that there is anthrax in the soil that the sheep are eating.
An experiment to test Louis' theory is tested. Louis vaccinates 25 sheep and does not vaccinate 25 others. Many people come to see if Pasteur is right, one being Dr. Joseph Lister. Sure enough, the vaccinated sheep lived and the other 25 died. This proved that Louis Pasteur found the cause and cure for anthrax.
As Pasteur and his wife celebrate his new accomplishments, Dr. Jean Martel asks if he can marry Louis' daughter, Annette. Everyone is happy, especially Louis. He proved many wrong including Dr. Radisse, who insisted that his theory was wrong since he met him.
Just as one tragedy is solved, another occurs. A village boy named Joseph Meister is bit by a dog with rabies. His worried mother and father seek help in Pasteur. Pasteur invites the boy to stay at his house, while he is determined to find a cure and treatment for the disease.
Louis Pasteur became frustrated and confused when he did not find a microorganism in the disease, like he did with anthrax. Dr. Charbonnet is so convinced that Pasteur is a failure that he even injects himself with rabies. He then shows off how the disease did not get him right away.