Louis Pasteur was born in 1822 to a family of modest means. Working for his doctorate in the laboratory of Antoine Balard, Pasteur at 26, was able to use the techniques of crystallography to explain the existence of stereoisomers of molecules in natural substances. Later Pasteur married and move to the town of Lille to become Dean and Professor of chemistry at the Faculty of Science. While in Lille, Louie Pasteur began a twenty year study of the process of fermentation. Beginning his research using the methods of a chemist, Pasteur soon realized he needed to develop new procedures and new ways of studying chemical reactions. Actually, he developed methodologies that would evolve into the discipline known as bacteriology, the study of bacteria. The age-old theological debate known as spontaneous generation was finally dispelled by Pasteur by proving that putrefaction and decay were caused by chemical reactions produced by microorganisms. Pasteur was able to demonstrate that the chemical conversion of sugars to alcohols or acids was performed by microorganisms.

Pasteur was to hold positions in several French universities throughout his life. His research with microorganisms led to significant contributions to the wine and silkworm industry. Louie Pasteur developed the technique of pasteurization to kill disease-causing microorganisms from liquids. He identified three different microorganisms that caused different diseases in the silkworm. His association of specific organisms with particular diseases, even though in silkworms rather than in humans, was an important first step in proving the germ theory of disease.

Later in life, Pasteur developed the process of attenuation. He was able to transfer and re-grow bacteria numerous times and in doing so, recognized that many times the bacteria became weakened. Pasteur soon realized that weakened strains of microorganisms could be used as vaccines. He is best known for his successful rabies vaccine.