Louis Pasteur (born December 27, 1822; died September 28, 1895) was a French scientist who worked in chemistry, pharmacy, and the study of tiny living things. He is best known for his discoveries about vaccination, how microorganisms cause fermentation, and a process called pasteurization, which was named after him. His research in chemistry helped scientists understand how to prevent diseases, which led to better hygiene, public health, and modern medicine. Pasteur’s work saved millions of lives by creating vaccines for rabies and anthrax. He is considered one of the founders of modern bacteriology and is 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 belief called spontaneous generation. In an experiment supported by the French Academy of Sciences, he showed that microorganisms could not grow in sterilized, sealed flasks but could grow in sterilized, open flasks. For this work, he received the Alhumbert Prize in 1862, worth 2,500 francs.
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. He is most famous for creating a method to treat milk and wine to stop bacteria, now called pasteurization. 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 had major effects on chemistry and medicine.
Pasteur led the Pasteur Institute, founded in 1887, until his death. His body was buried in a vault under the institute. Some records later showed he used tricky methods to beat his competitors.
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 primary school in 1831. He had difficulty reading and writing, which made learning challenging.
He was an average student early in his life and was not very focused on school. 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 live in a boarding school, but he missed home and returned in November.
In 1839, he entered the Collège Royal [fr] in Besançon to study philosophy and earned his Bachelor of Letters degree in 1840. He 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. He passed the baccalauréat scientifique (general science) degree in Dijon, where he earned his Bachelor of Science in Mathematics degree (Bachelier ès Sciences Mathématiques) in 1842, but his grade in chemistry was low.
In 1842, Pasteur took the entrance test for the École Normale Supérieure. During the test, he struggled with fatigue and felt most comfortable with physics and mathematics. He passed the first set 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 [fr] degree. In 1846, he became a professor of physics at the Collège de Tournon [fr] in Ardèche. However, the chemist Antoine Jérôme Balard wanted him to return to the École Normale Supérieure as a graduate laboratory assistant (agrégé préparateur). He joined Balard and began research in crystallography. In 1847, he submitted two theses: (a) Chemistry Thesis: "Recherches sur la capacité de saturation de l'acide arsénieux. Etudes des arsénites de potasse, de soude et d'ammoniaque." (b) Physics Thesis: "1. Études des phénomènes relatifs à la polarisation rotatoire des liquides. 2. Application de la polarisation rotatoire des liquides à la solution de diverses questions de chimie."
After briefly teaching physics at the Dijon Lycée in 1848, he became a professor of chemistry at the University of Strasbourg, where he met and married Marie Laurent, the daughter of the university's rector, in 1849. They had five children, but only two lived to adulthood; the other three died from typhoid.
Career
Pasteur became a professor of chemistry at the University of Strasbourg in 1848 and was made the head of the chemistry department in 1852.
In February 1854, to have time to complete work that could earn him the title of correspondent of the Institute, he used a medical note to get three months of paid time off. He extended this leave until August 1st, the start of exams. He told the Minister that he would return to take part in 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, he was named dean of the new science faculty at the University of Lille, where he began studying fermentation. At this time, he said his famous quote: "In the field of observation, chance favors only the prepared mind."
In 1857, he moved to Paris as director of scientific studies at the École Normale Supérieure. He led the school from 1858 to 1867 and made changes to improve the quality of scientific research. Exams became stricter, which led to better results, more competition, and greater respect for the school. However, some of his rules were strict, causing two major uprisings by students. During one protest, he ordered that a meat stew, which students had refused to eat, would be served every Monday. On another occasion, he threatened to expel students who smoked, and 73 out of 80 students left the school.
In 1863, he was made a professor of geology, physics, and chemistry at the École nationale supérieure des Beaux-Arts, a position he held 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 scientific 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. Solutions of this compound from living things could twist the plane of light passing through them, but chemically made tartaric acid did not have this 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 right hands and half like left hands. In solution, the right-handed crystals twisted light to the right, and the left-handed ones twisted it to the left. He concluded that the shape of the crystals and the arrangement of molecules inside them caused this twisting. The (2R,3R)- and (2S,3S)-tartrates were mirror images of each other but could not be overlapped. This discovery was the first demonstration of molecular chirality and explained isomerism.
Some historians say this work was Pasteur’s most important scientific contribution.
Pasteur studied fermentation while working at Lille. In 1856, a wine maker named M. Bigot, whose son was one of Pasteur’s students, asked for help with problems in making beetroot alcohol and souring wine. Pasteur began by repeating experiments by Theodor Schwann, who had shown that yeast was alive.
In August 1857, Pasteur sent a paper about lactic acid fermentation to the Société des Sciences de Lille. The paper was read three months later, and a memoir was published on November 30, 1857. In it, he wrote that just as yeast caused alcoholic fermentation, a specific type of yeast caused lactic acid fermentation.
Pasteur’s full work on alcoholic fermentation was published in 1858. He proved that yeast, not chemical breakdown, caused fermentation to produce alcohol from sugar. He also found that different microorganisms could make wine sour by producing lactic acid. In 1861, he observed that yeast fermented sugar more slowly when exposed to air, a discovery later called the Pasteur effect.
Pasteur showed that microorganisms caused spoilage in drinks like beer, wine, and milk. He developed a process where liquids were heated to kill bacteria and molds. He and Claude Bernard tested this method on blood and urine in 1862. Pasteur patented the process in 1865 to fight wine spoilage. This method became known as pasteurization and was later used for beer and milk.
Pasteur’s work on beverage spoilage led him to study how microorganisms cause disease in animals and humans. He suggested preventing microorganisms from entering the body, which inspired Joseph Lister to develop antiseptic surgical methods.
In 1866, Pasteur published Études sur le Vin, about wine diseases, and Études sur la Bière in 1876, about beer diseases.
In the early 1800s, Agostino Bassi showed that a fungus caused a disease in silkworms called muscardine. By 1865, two diseases, pébrine and flacherie, were harming silkworms in France, causing major losses. Pasteur worked in Alès from 1865 to 1870 to study these diseases.
Silkworms with pébrine had tiny particles on their bodies. At first, Pasteur thought these particles were a symptom, but in 1870, he found they were the cause (now known to be a microsporidian). He showed that pébrine was hereditary. To prevent it, he destroyed eggs if particles were found in moth pulp. He also found that bacteria caused flacherie, though it is now known to be caused by viruses. Hygiene helped prevent accidental flacherie, and healthy moths were used to avoid hereditary cases.
Pasteur’s experiments showed that grape skins were the source of yeast, and sterilized grapes did not ferment. He tested this by drawing juice from sterilized grapes and covering grapes with sterilized cloth, but neither produced wine in sterilized containers.
His findings challenged the idea of spontaneous generation, the belief that life could appear from non-living matter. Félix Archimède Pouchet, director of the Rouen Museum of Natural History, strongly opposed Pasteur’s work. To settle the debate, the French Academy of Sciences offered the Alhumbert Prize to prove or disprove spontaneous generation.
Pasteur disproved spontaneous generation through experiments. He boiled liquid in flasks, let air enter, and closed them. No organisms grew inside. When flasks were opened, dust caused growth, but fewer organisms grew at higher altitudes, where air had less dust. He used swan neck flasks, where air entered through a curved tube that trapped dust. No growth occurred unless the flask was tilted, allowing liquid to touch the contaminated neck. This showed that organisms came from dust, not from air or spontaneous generation.
These experiments helped disprove spontaneous generation. Pasteur presented his findings to the French Academy of Sciences in 1881, and they were published in 1882 as Mémoire Sur les corpuscules organisés qui existent dans l'atmosphère: Examen de la doctrine des générations spontanées.
Controversies
Louis Pasteur, a French hero, was 55 years old in 1878 when he quietly asked his family to never share his laboratory notebooks with anyone. His family followed his request, and all his papers remained private for many years. Since Pasteur did not allow others in his lab to keep notebooks, many details about his research stayed unknown until recently. In 1964, Pasteur’s grandson and last surviving male relative, Pasteur Vallery-Radot, gave the documents to the French national library. However, the papers were not available for study until after Vallery-Radot died in 1971. The library assigned the documents a catalog number in 1985.
In 1995, to mark the 100th anniversary of Pasteur’s death, a science historian named Gerald L. Geison published a book titled The Private Science of Louis Pasteur, in which he claimed that Pasteur had made misleading statements about his most important discoveries. A scientist named Max Perutz defended Pasteur in The New York Review of Books. Later, in 1998, a French immunologist named Patrice Debré wrote a book titled Louis Pasteur, in which he said that, despite Pasteur’s genius, he had some flaws. A review of Debré’s book noted that he described Pasteur as sometimes unfair, stubborn, and overly confident.
Before Pasteur, scientists studied fermentation. In the 1830s, researchers like Charles Cagniard-Latour, Friedrich Traugott Kützing, and Theodor Schwann used microscopes to examine yeast and concluded that it was a living organism. However, in 1839, scientists Justus von Liebig, Friedrich Wöhler, and Jöns Jacob Berzelius claimed that yeast was not alive and formed when air acted on plant juice.
In 1855, Antoine Béchamp, a chemistry professor at the University of Montpellier, studied sucrose solutions and believed that water caused fermentation. By 1858, he changed his view, saying that fermentation was linked to the growth of molds, which needed air to grow. Béchamp claimed he was the first to show that microorganisms caused fermentation.
Pasteur began his experiments in 1857 and published his findings in 1858 (in the Comptes Rendus Chimie journal, which was published after Béchamp’s paper in January 1858). Béchamp noted that Pasteur did not introduce new ideas or experiments. However, Béchamp may have known about Pasteur’s earlier work. Both scientists claimed they discovered fermentation first, and their disagreement lasted for many years.
Eventually, Béchamp lost the dispute, as noted in an BMJ obituary that said his name was "associated with bygone controversies as to priority which it would be unprofitable to recall." Béchamp promoted an incorrect theory called microzymes. According to K. L. Manchester, some people who opposed animal testing and supported alternative medicine promoted Béchamp and microzymes, falsely claiming that Pasteur copied Béchamp’s work.
Pasteur believed that succinic acid caused sucrose to invert. In 1860, Marcellin Berthelot isolated an enzyme called invertase and showed that succinic acid did not cause inversion. Pasteur argued that fermentation only happened in living cells. He and Berthelot debated the idea of vitalism, a belief that life requires special forces. Hans Buchner later discovered that a mixture of enzymes called zymase could cause fermentation, proving that enzymes inside cells drive the process. Eduard Buchner also found that fermentation could occur outside living cells.
Pasteur publicly claimed success in developing the anthrax vaccine in 1881. However, his supporter-turned-rival, Henry Toussaint, had already created the first vaccine. In 1879, Toussaint isolated the bacteria that caused chicken cholera (later named Pasteurella in honor of Pasteur) and shared samples with Pasteur. On July 12, 1880, Toussaint presented his successful use of an attenuated vaccine against anthrax in dogs and sheep to the French Academy of Sciences. Pasteur, feeling jealous, challenged Toussaint’s discovery by demonstrating his vaccination method in Pouilly-le-Fort on May 5, 1881. Pasteur gave a misleading account of how he prepared the anthrax vaccine, claiming he used a "live vaccine" when he actually used potassium dichromate to inactivate anthrax spores. His experiment was successful and helped him gain recognition and profit.
Pasteur’s experiments are often criticized for violating medical ethics, especially his vaccination of a boy named Meister. Pasteur had no experience in medical practice and did not hold a medical license. This lack of qualification harmed his professional reputation. His closest partner, Émile Roux, who had medical training, refused to participate in the clinical trial, likely because he believed it was unfair. However, Pasteur conducted the vaccination under the supervision of practicing physicians Jacques-Joseph Grancher, head of the Paris Children’s Hospital’s pediatric clinic, and Alfred Vulpian, a member of the Rabies Commission. Pasteur did not hold the syringe, but Grancher performed the injections and defended Pasteur before the French National Academy of Medicine.
Pasteur was also criticized for keeping his procedures secret and not conducting proper animal trials before testing his rabies vaccine on Meister. He claimed he kept the method private to ensure quality control. Later, he shared his procedures with a small group of scientists. Pasteur stated he had successfully vaccinated 50 rabid dogs before testing the vaccine on Meister. However, according to Geison, Pasteur’s notebooks show he had only vaccinated 11 dogs.
Awards and honours
Louis Pasteur was given 1,500 francs in 1853 by the Pharmaceutical Society for creating racemic acid. In 1856, the Royal Society of London honored him with the Rumford Medal for explaining racemic acid and its connection to polarized light. He received the Copley Medal in 1874 for his work on fermentation. In 1869, he became a Foreign Member of the Royal Society.
The French Academy of Sciences gave Pasteur the Montyon Prize in 1860 for work in experimental physiology. He also received the Jecker Prize in 1861 and the Alhumbert Prize in 1862 for proving that life does not appear 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 this role until 1889. In 1866, he was made an honorary member of the Manchester Literary and Philosophical Society.
In 1873, Pasteur was elected to the Académie Nationale de Médecine and became a commander in the Brazilian Order of the Rose. In 1881, he joined the Académie française after a seat became available. He received the Albert Medal from the Royal Society of Arts in 1882 and became a member of the Royal Netherlands Academy of Arts and Sciences in 1883. In 1885, he was elected to the American Philosophical Society. In 1886, the Ottoman Sultan Abdul Hamid II gave him the Order of the Medjidie and 10,000 Ottoman liras. He received the Cameron Prize in 1889 and the Leeuwenhoek Medal in 1895 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, such as in Palo Alto and Irvine, California; Boston and Polk, Florida; Jonquière, Québec; San Salvador de Jujuy and Buenos Aires, Argentina; Great Yarmouth, United Kingdom; Jericho and Wulguru, Australia; Phnom Penh, Cambodia; Ho Chi Minh City and Da Nang, Vietnam; Batna, Algeria; Bandung, Indonesia; Tehran, Iran; Warsaw, Poland; Odesa, Ukraine; Milan, Italy; and Bucharest, Cluj-Napoca, and Timișoara, Romania. In Vietnam, Avenue Pasteur in Saigon is one of the few streets with a French name. In Boston, Avenue Louis Pasteur was named in his honor.
The Institut Pasteur and Université Louis Pasteur were named after him. Schools such as Lycée Pasteur in France and Lycée Louis Pasteur in Canada are also named in his honor. In South Africa, hospitals like the Louis Pasteur Private Hospital in Pretoria and Life Louis Pasteur Private Hospital in Bloemfontein are named after him. The Louis Pasteur University Hospital in Košice, Slovakia, is also named after him.
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 cast in 1984 by Artworks Foundry.
The UNESCO/Institut Pasteur Medal was created 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, people from many countries helped raise money to start the Pasteur Institute. The institute’s goal was to treat rabies and study diseases. It officially opened on November 14, 1888. Pasteur brought together scientists with different skills. The first five departments were led by Émile Duclaux, Charles Chamberland, Élie Metchnikoff, Jacques-Joseph Grancher, and Émile Roux. In 1889, Roux taught the first microbiology course in the world. 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 Pasteur’s scientific assistant. Together, they had five children. Three of them died before reaching adulthood. Their eldest daughter, Jeanne, was born in 1850. She died from typhoid fever at the age of 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 23 May 1866 at the age of 12. Only two of their children, Jean Baptiste (born in 1851) and Marie Louise (born in 1858), survived to adulthood. Jean Baptiste later became a soldier during the Franco-Prussian War between France and Prussia.
Louis Pasteur Vallery-Radot, his grandson, wrote that Pasteur retained only a belief in spiritualism from his Catholic background but did not practice religion. However, Catholic observers claimed that Pasteur remained a devoted Christian throughout his life. His son-in-law wrote in a biography of him:
The Literary Digest of 18 October 1902 reported that Pasteur said he prayed while working.
Maurice Vallery-Radot, a grandson of the brother of Pasteur’s son-in-law and a Catholic, believed that Pasteur remained fundamentally Catholic. According to both Louis Pasteur Vallery-Radot and Maurice Vallery-Radot, the 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 actually from Pasteur. Maurice Vallery-Radot noted that the false quote first appeared shortly after Pasteur’s death. Despite his belief in God, some people said Pasteur’s views were closer to those of a freethinker rather than a Catholic. He was described as more spiritual than religious and believed science should not be mixed with religion.
In 1868, Pasteur suffered a severe stroke that paralyzed the left side of his body, but he recovered. A stroke or uremia in 1894 severely affected his health. He did not fully recover and died on 28 September 1895 near Paris. He received a state funeral and was initially buried in the Cathedral of Notre Dame. Later, his remains were moved to the Pasteur Institute in Paris, where they are now kept in a vault decorated with Byzantine mosaics depicting his scientific achievements.