Louis Pasteur

Louis Pasteur established that microorganisms cause disease and fermentation, and developed vaccines against three of them. Born in Dole in 1822, the son of a tanner and a sergeant in Napoleon's army, he was an unremarkable schoolboy who wanted to be a painter, and took degrees in physics and chemistry. His first discovery was made at twenty-six. Examining crystals of tartrate, he found two mirror-image forms and separated them by hand under a microscope, establishing molecular chirality — the foundation of stereochemistry. He was asked by a distiller to investigate why beetroot alcohol was souring, and found that fermentation is caused by living yeast and that souring is caused by different organisms. That led to the general germ theory: that specific microbes cause specific processes, including disease. He disproved spontaneous generation in 1859 with swan-neck flasks, which admitted air but trapped dust, and in which sterile broth remained sterile indefinitely. He developed gentle heating to kill spoilage organisms in wine, beer and milk, which is called pasteurisation. He saved the French silk industry by identifying two parasitic diseases of silkworms. He then produced vaccines by attenuating pathogens — chicken cholera by accident, from a culture left over a holiday, then anthrax, demonstrated publicly at Pouilly-le-Fort in 1881 with fifty sheep. In July 1885 he treated Joseph Meister, a nine-year-old bitten by a rabid dog, with a series of injections of dried spinal cord. He was not a physician and the treatment was unlicensed. The boy lived. The Pasteur Institute opened in 1888. He died in 1895.

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