Louis Pasteur (1822 – 1895) was a French chemist and microbiologist who investigated the causes of diseases and developed vaccines to prevent them. His experiments proved the theory that disease was caused by germs. His discoveries encouraged the principles of sanitation that reduced mortality from puerperal fever, an infection contracted by mothers who were exposed to unsanitary conditions after the delivery of their babies. He also created the first vaccines for rabies and anthrax. By inoculating people with weakened forms of the microorganisms, he prevented full-blown cases which would be fatal.
Pasteur also proved that fermentation is caused by the growth of micro-organisms which was responsible for spoiling beverages, such as beer, wine and milk. He developed a process, called pasteurization, in which liquids were heated to kill most bacteria and moulds in liquids.