"Pasteur inoculating a man with the rabies virus," chromolithograph, circa 1895/1900. Louis Pasteur (December 27, 1822 - September 28, 1895) was a French chemist and bacteriologist who founded the science of microbiology. Pasteur discovered that disease could be caused by bacteria transmitted from person to person (the germ theory of disease). He also developed vaccines for rabies and anthrax. Pasteur also found that lightly heating food and beverages could preserve them from souring. This pasteurization process is now widely used in the food industry. As a chemist, Pasteur discovered that some crystals had two forms, one which would rotate plane-polarized light to the left, and the other would rotate light to the right. This led to the study of stereochemistry.