Louis Pasteur

Louis Pasteur showed that fermentation and spoilage are caused by living microorganisms, not by spontaneous generation, and that heating could kill them, the process now called pasteurization. His work built the case for the germ theory of disease and transformed medicine, surgery, and public health. He developed vaccines for anthrax and, most famously, for rabies, which he first used on a boy bitten by a rabid dog in 1885. He founded the Pasteur Institute in Paris. Later historians, reading his notebooks, found that some of his public demonstrations were less clean than he claimed, though the results held up.