Louis Pasteur
French chemist and microbiologist
Biography
Louis Pasteur (Dole, 1822 - Marnes-la-Coquette, 1895) was a French chemist and microbiologist and one of the founding figures of modern microbiology. His research on fermentation, spontaneous generation and infectious disease led to pasteurization and to the first principles of vaccination with weakened microorganisms. He matters to the history of food because pasteurization transformed the preservation of wine, beer and milk, and because much of his work began with practical problems raised by industry. He became a member of the French Academy in 1881.
The son of a tanner, he grew up in the Franche-Comté and in Arbois, where he showed more interest in drawing and painting than in natural sciences. After studying in Besançon, he took his bachelor's degree in mathematical sciences at Dijon in 1842, with only a middling mark in chemistry. A first attempt to enter the École Normale Supérieure in Paris ended badly, but he was admitted in 1843 and turned towards chemistry. In 1847 he defended his doctorate in science with two theses, one in chemistry and one in physics, both concerned with the rotation of polarized light by liquids. The following year he studied tartaric acid and found that its crystals came in mirror-image forms, which explained why some samples rotated light in one direction and others in the opposite direction. That discovery opened the way to stereochemistry and to the idea of molecular asymmetry.
His academic career moved through Dijon and Strasbourg, where he taught chemistry and in 1849 married Marie Laurent, the daughter of the university's rector. They had five children, but three died of typhoid, a loss that shaped family life. In 1854 he was appointed dean of the new faculty of sciences at Lille, where he began studying fermentation at the request of a local manufacturer whose wine and beetroot alcohol were souring. It was there that he made his well-known remark that chance favours only the prepared mind. In 1857 he moved to Paris as director of scientific studies at the École Normale Supérieure, where he introduced demanding reforms that caused friction with students.
In Lille he showed that alcoholic fermentation was the work of living yeasts, not simply a chemical breakdown as Berzelius and Liebig had argued. He also identified microorganisms that produced lactic acid and soured wine. From this work came the method of heating wine, beer and milk moderately in sealed containers to destroy the microbes that spoiled them. Pasteur patented the procedure in 1865, and it was soon applied to other foods. His name became attached to the process, which still underpins the safety of many dairy products and bottled drinks today.
To answer the theory of spontaneous generation, Pasteur designed flasks with long, curved necks that let air in but trapped dust. Boiled broths in them stayed clear, whereas they spoiled once the liquid was tilted to touch the contaminated neck. His results, defended against objections from Pouchet and others, became the basis of the principle omne vivum ex vivo. Around 1865 the French government asked him to study the epidemic that was ruining silk production in southern France. Pasteur admitted he knew nothing about silkworms, but he believed that lacking preconceptions might help him. After years of microscopic observation he distinguished two diseases, pébrine and flacherie, and recommended selecting healthy eggs and destroying infected ones. His method helped save much of the regional silk industry, although flacherie proved harder to control. During this period he suffered a cerebral haemorrhage that left him partly paralysed on his left side.
His germ theory of infectious disease challenged traditional medicine. Joseph Lister applied related ideas in surgery and developed antisepsis, while Pasteur urged that instruments and dressings in military hospitals be boiled. His work on fowl cholera in 1880 was a turning point. According to the most widely repeated story, a culture left unused for weeks produced birds that survived a later infection. Pasteur read this as a form of immunity similar to the one Edward Jenner had described. To honour Jenner, he called the procedure vaccination and extended the word vaccine to all preparations of weakened microorganisms. In 1881 he demonstrated a vaccine against anthrax at Pouilly-le-Fort, though his rivalry with Robert Koch, who criticised his methods and rigour, was intense.
His rabies work is the best known to the public. In 1885, when his preparation still had a limited experimental basis, he decided to treat the boy Joseph Meister, who had been bitten by a rabid dog. Pasteur was not a physician and took a legal and personal risk, but the boy recovered without developing the disease. The episode made him famous. In 1888 the Pasteur Institute opened in Paris, and he directed it until his death; he was buried in its crypt. He was a devout Catholic who kept his faith throughout his life, a point his biographers stress without separating it from his scientific work.
His legacy spans food preservation, medicine and biology, but his reputation has also been debated. In 1878 he asked that his laboratory notebooks not be published, and in 1964 they were deposited at the Bibliothèque nationale de France, where they can now be consulted. His name survives in the Pasteur Institute, in street names, in a lunar crater, and in the process that bears his name, while World Rabies Day is held every 28 September, the date of his death.
Key contributions
- Stereochemistry: molecular asymmetry and optical isomerism, explained through the crystal forms of tartrates.
- Pasteurization: moderate heating of wine, beer and milk to destroy microorganisms, a method still central to the food industry.
- Experimental demonstration that microorganisms do not arise spontaneously, a cornerstone of modern microbiology.
- Germ theory of infectious disease, which guided hospital hygiene and antisepsis.
- Vaccines made from weakened microorganisms against fowl cholera, anthrax and rabies, and the word “vaccine” in honour of Jenner.
- Research on pébrine in southern French sericulture, with a method of selecting healthy silkworm eggs.