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Louis Pasteur (1822-95)

The French chemist Louis Pasteur developed germ theory, which became central to our understanding of disease. Using experiments and microscopes, Pasteur found that liquids such as beer and milk went off because of the rapid multiplication of very small organisms - germs - in those liquids. He investigated further and found that many of these micro-organisms could be killed by heating the liquid: a preservation method now called ‘pasteurisation’.

Pasteur applied his explanation of decaying liquids to solid matter as well. He showed experimentally that the decay of meat was caused by microbes. The chemist argued that this could explain disease as well as decay, claiming that disease was caused by the multiplication of germs in the body. He investigated his theory using silkworms and went on to develop a new form of vaccination - by chance he discovered that germs which had been weakened by long exposure to the air caused immunity to cholera in chickens. Pasteur’s work made a significant contribution to the development of the first ‘magic bullets’, chemicals developed to attack specific germs.


G Geison, The Private Science of Louis Pasteur (Princeton, NJ: Princeton University Press, 1995)

B Latour, The Pasteurization of France, translated by A Sheridan and J Law, (Cambridge, Mass.: Harvard University Press, 1988)

I Pasteur, 'Recherches sur la putrefaction', Comptes Rendus de l'Académie des Sciences, 66 (1863), pp 1189-1194

L E Robbins, Louis Pasteur and the Hidden World of Microbes (New York: Oxford University Press, 2001)

L Ward, 'The cult of relics: Pasteur material at the Science Museum', Medical History, 38/1 (1994), pp 52-72



A tiny single-celled living organism too small to be seen by the naked eye. Micro-organisms that cause disease are called bacteria.