Louis Pasteur

About this figure

Louis Pasteur (1822–1895) was a French chemist and microbiologist whose experiments established the germ theory of disease and gave rise to some of the most consequential practical applications in the history of science, including pasteurization and modern vaccination. Trained as a chemist, he first made his scientific name studying the molecular structure of tartaric acid crystals, work that led him toward questions of fermentation when French industries asked him to investigate why wine, beer, and vinegar sometimes spoiled during production.

Pasteur's studies of fermentation, including his research collected in Studies on Fermentation: The Diseases of Beer, showed that fermentation and spoilage were caused by living microorganisms rather than purely chemical processes, and that different microbes produced different, identifiable effects, some desirable and some harmful to the finished product. This work led directly to pasteurization, the process of heating a liquid enough to kill most spoilage-causing microorganisms without significantly altering its taste, now used worldwide for milk and other foods. His fermentation research also brought him into direct conflict with the long-standing theory of spontaneous generation, the idea that living organisms could arise spontaneously from non-living matter; Pasteur's carefully designed experiments with sealed, curved-neck flasks demonstrated that microbial growth in a sterilized liquid required outside contamination, dealing a decisive blow to the theory.

Pasteur extended these findings from beverages to disease, arguing that specific microorganisms caused specific diseases in silkworms, livestock, and eventually humans, and he developed effective vaccines against anthrax in livestock and, most famously, against rabies, successfully treating a boy bitten by a rabid dog in 1885 in a case that made him internationally famous. The Pasteur Institute, founded in Paris in 1887 largely on the strength of that success, became and remains a leading center for microbiological and immunological research. Pasteur suffered a series of strokes beginning in his mid-forties that partially paralyzed him but did not end his research career, and he continued directing scientific work until his death in 1895.

Written by Epoch Voices. Not the figure’s own words.