Louis Pasteur made several scientific contributions, including his invention of pasteurization and vaccines and his development of the germ theory. As a microbiologist and chemist, he sought to create a solution to the spoiling of milk, wine and beer. He understood that bacteria introduced from the environment led to spoiling and invented pasteurization, in which the product is boiled and then cooled to kill bacteria and extend the shelf life.
Pasteur also developed the theory of viruses and germs by proposing sickness and infection was caused by outside bacteria, similar to the spoiling of milk. Prior to Pasteur, surgeons rarely washed their hands or instruments before operating on a patient, and surgery was thus considered a death sentence for the most part. By inventing a sterilization process for instruments and insisting that surgeons wash their hands, Pasteur saved countless patients from preventable infection.
Pasteur is also known for applying his germ theory to invent vaccinations. Pasteur weakened a germ in the lab and reintroduced it to a patient to build immunity, successfully creating vaccines for tuberculosis, rabies, anthrax and cholera. His successes led to the foundation of the Pasteur Institute in Paris, France. In 1865, Pasteur helped rescue the French silk industry by proving that microbes were attacking healthy silkworm eggs.