Louis Pasteur (born December 27, 1822; died September 28, 1895) was a French scientist who worked as a chemist, pharmacist, and microbiologist. He is best known for discovering the principles of vaccination, microbial fermentation, and pasteurization, a process named after him. His research in chemistry helped people understand how diseases are caused and how they can be prevented. This work laid the foundation for modern medicine, public health, and hygiene. Pasteur’s discoveries, including vaccines for rabies and anthrax, saved millions of lives. He is considered one of the founders of modern bacteriology and is often called the “father of bacteriology” and the “father of microbiology,” along with Robert Koch and Antonie van Leeuwenhoek.

Pasteur proved that life does not come from nothing, a theory called spontaneous generation. In an experiment supported by the French Academy of Sciences, he showed that sterilized and sealed flasks did not develop life, while sterilized but open flasks allowed microorganisms to grow. For this work, he received the Alhumbert Prize worth 2,500 francs in 1862.

Pasteur helped develop the germ theory of disease, which explained that germs cause illness. His experiments showed that killing germs could prevent disease, supporting this theory and its use in medicine. He is most famous for creating pasteurization, a method to treat milk and wine to stop bacteria from growing. Pasteur also made important discoveries in chemistry, including how certain crystals have asymmetrical shapes and how they change over time. His early work on sodium ammonium tartrate helped start the study of optical isomerism, which influenced many areas of science, including medicine.

Pasteur was the director of the Pasteur Institute, founded in 1887, until his death. His body was buried in a vault under the institute. Although his experiments were groundbreaking, some of his work has been questioned. Later reviews of his notes showed that he may have misled others to gain an advantage over his rivals.

Early life and education

Louis Pasteur was born on December 27, 1822, in Dole, Jura, France, to a Catholic family. His father was a poor tanner, and he was the third child of Jean-Joseph Pasteur and Jeanne-Etiennette Roqui. The family moved to Marnoz in 1826 and then to Arbois in 1827. Pasteur began attending primary school in 1831. He had difficulty reading and writing.

He was an average student early in life and did not focus much on schoolwork. Instead, he enjoyed fishing and drawing. He created many pastels and portraits of his parents, friends, and neighbors. Pasteur attended secondary school at the Collège d'Arbois. In October 1838, he went to Paris to join a boarding school but felt homesick and returned to Arbois in November.

In 1839, he entered the Collège Royal at Besançon to study philosophy and earned his Bachelor of Letters degree in 1840. He later worked as a tutor at the Besançon college while continuing his science studies with a focus on mathematics. He failed his first examination in 1841. However, he passed the baccalauréat scientifique (general science) exam in Dijon and earned his Bachelor of Science in Mathematics degree in 1842, though his chemistry grade was low.

In 1842, Pasteur took the entrance test for the École Normale Supérieure. During the test, he struggled with fatigue but felt more confident with physics and mathematics. He passed the first round of tests but decided not to continue because his ranking was low. He returned to Paris to prepare for the test again. He also attended classes at the Lycée Saint-Louis and lectures by Jean-Baptiste Dumas at the Sorbonne. In 1843, he passed the test with a high ranking and entered the École Normale Supérieure. Later, he studied under Jean-Baptiste Boussingault at the Conservatoire national des arts et métiers. In 1845, he received the licencié ès sciences degree. In 1846, he became a professor of physics at the Collège de Tournon in Ardèche. However, chemist Antoine Jérôme Balard wanted him to return to the École Normale Supérieure as a graduate laboratory assistant. Pasteur joined Balard and began research in crystallography. In 1847, he submitted two theses: (a) Chemistry Thesis: "Research on the saturation capacity of arsenious acid. Studies of potassium, sodium, and ammonium arsenites"; (b) Physics Thesis: "1. Studies of phenomena related to the optical rotation of liquids. 2. Application of optical rotation of liquids to solving various chemistry questions."

After briefly teaching physics at the Dijon Lycée in 1848, he became a professor of chemistry at the University of Strasbourg. There, he met and married Marie Laurent, the daughter of the university's rector, in 1849. They had five children, but only two survived to adulthood; the other three died of typhoid.

Career

Louis Pasteur was given a job as a professor of chemistry at the University of Strasbourg in 1848. In 1852, he became the head of the chemistry department there.

In February 1854, Pasteur used a medical certificate to get three months of paid leave so he could work on projects that might earn him the title of correspondent of the Institute. He extended the leave until August 1, the start of exams. He told the Minister he would return to take the exams to avoid causing problems for the school and to ensure someone else would not receive a payment of 600 to 700 francs.

In 1854, Pasteur was named dean of the new science faculty at the University of Lille. There, he began studying fermentation. He said, “In the field of observation, chance favors only the prepared mind.”

In 1857, Pasteur moved to Paris as the director of scientific studies at the École Normale Supérieure. He led the school from 1858 to 1867 and made changes to improve scientific work. Exams became stricter, which led to better results, more competition, and greater prestige. However, some of his rules were strict, and this caused two major student uprisings. During one, called the “bean revolt,” he ordered that a mutton stew, which students had refused to eat, would be served every Monday. On another occasion, he threatened to kick out any student who smoked, and 73 of the 80 students in the school left.

In 1863, Pasteur was appointed professor of geology, physics, and chemistry at the École nationale supérieure des Beaux-Arts. He held this position until 1867. In 1867, he became the head of organic chemistry at the Sorbonne but later left due to poor health. That same year, the École Normale’s laboratory of physiological chemistry was created at his request, and he directed it from 1867 to 1888. In 1887, he founded the Pasteur Institute in Paris and remained its director for the rest of his life.

Research

Louis Pasteur began his work as a chemist at the École Normale Supérieure and later at Strasbourg and Lille. He studied the chemical, optical, and crystallographic properties of a group of compounds called tartrates.

In 1848, Pasteur solved a problem about tartaric acid. A solution of this compound from living things could twist the direction of light passing through it. However, tartaric acid made in the lab had no such effect, even though its chemical reactions and composition were the same.

Pasteur noticed that tartrate crystals had small faces. He found that in racemic mixtures of tartrates, half the crystals were shaped like a right hand and half like a left hand. In solution, the right-handed crystals twisted light to the right (dextrorotatory), and the left-handed ones twisted it to the left (levorotatory). He concluded that the shape of the crystals and the arrangement of molecules caused this effect. The (2R,3R)- and (2S,3S)-tartrates were mirror images of each other but could not be overlapped. This was the first time molecular chirality and isomerism were explained.

Some historians say Pasteur’s work on tartrates was his most important scientific discovery.

Pasteur studied fermentation while working at Lille. In 1856, a wine maker named M. Bigot, whose son was a student of Pasteur, asked for help with problems in making beetroot alcohol. Pasteur repeated experiments by Theodor Schwann, who had shown earlier that yeast, a type of living cell, was involved in fermentation.

In August 1857, Pasteur sent a paper about lactic acid fermentation to the Société des Sciences de Lille. A memoire was published in November 1857. He wrote that just as yeast caused alcoholic fermentation, a different microorganism caused lactic acid fermentation.

Pasteur’s full work on alcoholic fermentation was published in 1858. He proved that fermentation was caused by living cells, not by chemical breakdown as some scientists had thought. He also showed that lactic acid could make wine sour if another microorganism was present. In 1861, he found that yeast fermented sugar more slowly when exposed to air. This slower rate became known as the Pasteur effect.

Pasteur discovered that microorganisms caused spoilage in drinks like beer, wine, and milk. To stop this, he heated liquids to 60–100°C, killing most bacteria and molds. This process, called pasteurization, was patented in 1865. It was later used for milk and beer.

Pasteur’s work on beverage spoilage led him to study how microorganisms cause disease in animals and humans. His ideas helped Joseph Lister develop antiseptic methods in surgery.

In 1866, Pasteur published Études sur le Vin (Studies on Wine), and in 1876, Études sur la Bière (Studies on Beer).

In the early 1800s, Agostino Bassi showed that a fungus caused a disease in silkworms called muscardine. By the 1860s, two other diseases, pébrine and flacherie, were killing silkworms in France. In 1865, Pasteur studied these diseases for five years.

He found that silkworms with pébrine had tiny particles on their bodies. At first, he thought the particles were a symptom, but later he realized they caused the disease. Today, it is known that a microsporidian, a type of tiny organism, is the real cause. Pasteur also showed that pébrine was hereditary. He developed a method to prevent it by checking silkworm eggs for these particles. He also linked flacherie to bacteria, though it is now known that viruses are the main cause.

Pasteur showed that the skin of grapes was the source of yeast, and that sterilized grapes did not ferment. He tested this by drawing juice from under the skin with sterilized needles and covering grapes with sterilized cloth. Neither method produced wine in sterilized containers.

Pasteur’s findings challenged the idea of spontaneous generation, which claimed that living things could appear from non-living matter. A scientist named Félix Pouchet argued that air could cause life to form in liquids. To settle the debate, the French Academy of Sciences offered a prize for experiments proving or disproving spontaneous generation.

Pasteur repeated experiments by Francesco Redi and Lazzaro Spallanzani, who had previously shown that air carried microbes. He boiled liquid in flasks and let air enter. When the flasks were closed, no organisms grew. When opened, dust caused growth. At higher altitudes, fewer organisms grew, showing less dust in the air.

Pasteur used swan-neck flasks, which allowed air to enter but trapped dust. No organisms grew unless the flasks were tilted, letting liquid touch the contaminated neck. This proved that microbes came from the air, not from spontaneous generation.

These experiments helped disprove the theory of spontaneous generation. In 1881, Pasteur presented his findings to the French Academy of Sciences. His work was published in 1882 as Mémoire Sur les corpuscules organisés qui existent dans l'atmosphère: Examen de la doctrine des générations spontanées (Account of Organized Corpuscles in the Atmosphere: Examination of the Doctrine of Spontaneous Generation).

Controversies

Louis Pasteur, a famous French scientist, was 55 years old in 1878 when he quietly asked his family to keep his laboratory notebooks private. His family followed his request, and all his papers remained hidden for many years. Since Pasteur did not allow others in his lab to keep notebooks, much of his research remained unknown until the 20th century. In 1964, Pasteur’s grandson, Pasteur Vallery-Radot, gave the documents to the French National Library. However, the papers were not available for study until after Vallery-Radot’s death in 1971. The documents received a catalog number only in 1985.

In 1995, a scientist named Gerald L. Geison published a book titled The Private Science of Louis Pasteur, in which he analyzed Pasteur’s private notes and claimed that Pasteur had sometimes given incorrect information about his discoveries. Another scientist, Max Perutz, defended Pasteur in The New York Review of Books. Later, in 1998, French immunologist Patrice Debré wrote a book titled Louis Pasteur, in which he noted that despite Pasteur’s brilliance, he had some flaws. A review of Debré’s book mentioned that Pasteur was sometimes described as unfair, stubborn, and unkind.

Before Pasteur, scientists studied fermentation. In the 1830s, Charles Cagniard-Latour, Friedrich Traugott Kützing, and Theodor Schwann used microscopes to examine yeast and concluded that yeast was a living organism. In 1839, Justus von Liebig, Friedrich Wöhler, and Jöns Jacob Berzelius argued that yeast was not alive but formed when air acted on plant juice.

In 1855, Antoine Béchamp, a chemistry professor, tested sucrose solutions and believed water caused fermentation. By 1858, he changed his view, stating that fermentation depended on mold growth, which needed air. Béchamp claimed to be the first to show that microorganisms caused fermentation.

Pasteur began his experiments in 1857 and published his findings in 1858. Béchamp noted that Pasteur did not introduce new ideas or experiments. However, Béchamp may have known about Pasteur’s earlier work. A long disagreement about who discovered fermentation’s causes lasted for many years.

Eventually, Béchamp’s reputation suffered because he promoted an incorrect theory called microzymes. Some people later claimed that Pasteur had copied Béchamp’s work, but these claims were not supported by evidence.

Pasteur believed that succinic acid caused sucrose to break down. In 1860, Marcellin Berthelot isolated an enzyme called invertase and proved that succinic acid did not cause this process. Pasteur argued that fermentation only happened in living cells, while Berthelot opposed the idea of vitalism, which claimed life required special forces. Hans Buchner later discovered that enzymes inside cells, not living cells themselves, caused fermentation. Eduard Buchner also showed that fermentation could occur outside living cells.

In 1881, Pasteur publicly claimed credit for developing the anthrax vaccine. However, Henry Toussaint, a scientist who had become a rival, had already created the first vaccine. Toussaint identified the bacteria that caused chicken cholera (later named Pasteurella in Pasteur’s honor) in 1879 and shared samples with Pasteur. In 1880, Toussaint successfully tested an attenuated vaccine against anthrax in dogs and sheep. Pasteur, feeling jealous, later claimed he had developed the vaccine himself. He used potassium dichromate to inactivate anthrax spores, a method similar to Toussaint’s. Pasteur’s public demonstration of the vaccine was successful and helped him gain fame and financial benefits.

Pasteur’s experiments, especially his vaccination of a boy named Meister, have been criticized for ethical reasons. He had no medical training or license, which some argue harmed his reputation. His partner Émile Roux, who had medical qualifications, refused to help with the clinical trial, likely because he believed it was unfair. However, Pasteur’s work was supervised by practicing physicians, including Jacques-Joseph Grancher and Alfred Vulpian. Grancher performed the injections and defended Pasteur before the French National Academy of Medicine.

Pasteur also faced criticism for keeping his methods secret and not testing them thoroughly on animals before human trials. He claimed secrecy was necessary to maintain quality control. Later, he shared his procedures with a small group of scientists. Pasteur wrote that he had vaccinated 50 rabid dogs before treating Meister, but Geison’s analysis of Pasteur’s notebooks showed that only 11 dogs had been vaccinated.

Awards and honours

Louis Pasteur received 1,500 francs in 1853 from the Pharmaceutical Society for creating racemic acid. In 1856, the Royal Society of London gave him the Rumford Medal for explaining how racemic acid interacts with polarized light. In 1874, he was awarded the Copley Medal for his research on fermentation. He became a Foreign Member of the Royal Society in 1869.

The French Academy of Sciences honored Pasteur with the Montyon Prize in 1860 for his work in experimental physiology. He also received the Jecker Prize in 1861 and the Alhumbert Prize in 1862 for proving that life does not arise from non-living matter. Though he was not chosen for membership in 1857 and 1861, he joined the mineralogy section of the academy in 1862. He became a permanent secretary of the physical science section in 1887 and held the role until 1889. In 1866, he was elected to honorary membership in the Manchester Literary and Philosophical Society.

In 1873, Pasteur was elected to the Académie Nationale de Médecine and received the Brazilian Order of the Rose. In 1881, he joined the Académie française, a seat previously held by Émile Littré. He received the Albert Medal from the Royal Society of Arts in 1882. In 1883, he became a member of the Royal Netherlands Academy of Arts and Sciences. In 1885, he was elected to the American Philosophical Society. In 1886, the Ottoman Sultan Abdul Hamid II awarded him the Order of the Medjidie and 10,000 Ottoman liras. In 1889, he received the Cameron Prize for Therapeutics from the University of Edinburgh. In 1895, he was given the Leeuwenhoek Medal for his work in microbiology.

Pasteur was made a Chevalier of the Legion of Honour in 1853, promoted to Officer in 1863, Commander in 1868, Grand Officer in 1878, and Grand Cross of the Legion of Honour in 1881.

Many places around the world have streets named after him, including cities in the United States, Canada, France, Argentina, Vietnam, and other countries. The Avenue Pasteur in Saigon, Vietnam, and Avenue Louis Pasteur in Boston, Massachusetts, are examples.

The Institut Pasteur and Université Louis Pasteur were named in his honor. Schools such as Lycée Pasteur in France and Lycée Louis Pasteur in Canada are also named after him. Hospitals in South Africa, Slovakia, and other countries bear his name.

A statue of Pasteur stands at San Rafael High School in California. A bronze bust of him is displayed at the French Campus of Kaiser Permanente’s San Francisco Medical Center. The sculpture was designed by Harriet G. Moore and made by Artworks Foundry in 1984.

The UNESCO/Institut Pasteur Medal was created in 1995, 100 years after Pasteur’s death. It is given every two years to recognize research that improves human health.

Henri Mondor, a French academician, said, “Louis Pasteur was not a doctor or surgeon, but no one has done more for medicine and surgery than he has.”

After creating the rabies vaccine, Pasteur proposed an institute to study and treat rabies. In 1887, fundraising for the Pasteur Institute began, with support from many countries. The institute’s official purpose was to treat rabies and study contagious diseases. It opened on November 14, 1888. Scientists from different fields worked there. The first five departments were led by Émile Duclaux (microbiology), Charles Chamberland (hygiene), Élie Metchnikoff (microbiology), Jacques-Joseph Grancher (rabies), and Émile Roux (microbiology). Roux taught the first microbiology course in 1889, called Cours de Microbie Technique. Since 1891, the Pasteur Institute has expanded to 32 locations in 29 countries worldwide.

Personal life

Louis Pasteur married Marie Pasteur (née Laurent) in 1849. Marie was the daughter of the rector of the University of Strasbourg and worked as a scientific assistant to Louis. Together, they had five children. Three of their children died before reaching adulthood. Their oldest daughter, Jeanne, was born in 1850. She died from typhoid fever at age 9 while attending a boarding school in Arbois in 1859. In 1865, their 2-year-old daughter, Camille, died from a liver tumor. Shortly after, they decided to bring their daughter Cécile home from boarding school, but she also died from typhoid fever on May 23, 1866, at age 12. Only two children, Jean Baptiste (born in 1851) and Marie Louise (born in 1858), lived to adulthood. Jean Baptiste later became a soldier in the Franco-Prussian War between France and Prussia.

Louis Pasteur Vallery-Radot, his grandson, wrote that Pasteur kept only a spiritual belief from his Catholic background and did not practice religion. However, Catholic observers claimed Pasteur remained a devoted Christian throughout his life. His son-in-law wrote in a biography about Pasteur:

The Literary Digest of October 18, 1902, reported that Pasteur said he prayed while working.

Maurice Vallery-Radot, a grandson of Pasteur’s brother-in-law and a Catholic, believed Pasteur remained fundamentally Catholic. Both Louis Pasteur Vallery-Radot and Maurice Vallery-Radot stated that a famous quote often attributed to Pasteur—“The more I know, the more nearly is my faith that of the Breton peasant. Could I but know all, I would have the faith of a Breton peasant’s wife”—is not genuine. Maurice Vallery-Radot noted this false quote first appeared shortly after Pasteur’s death. Despite believing in God, some say Pasteur viewed himself as a freethinker rather than a Catholic, a spiritual person rather than a religious one. He also believed science and religion should not be mixed.

In 1868, Pasteur suffered a serious stroke that paralyzed the left side of his body but later recovered. In 1894, he had another serious illness that greatly weakened his health. He did not fully recover and died on September 28, 1895, near Paris. He received a state funeral and was first buried in the Cathedral of Notre Dame. Later, his remains were moved to a vault at the Pasteur Institute in Paris, where mosaics in the style of Byzantine art depict his scientific achievements.