Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist, pharmacist, and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation, and pasteurization, the last of which was named after him. His research in chemistry led to remarkable breakthroughs in the understanding of the causes and preventions of diseases, which laid down the foundations of hygiene, public health and much of modern medicine. Pasteur's works are credited with saving millions of lives through the developments of vaccines for rabies and anthrax. He is regarded as one of the founders of modern bacteriology and has been honored as the "father of bacteriology" and the "father of microbiology" (together with Robert Koch; the latter epithet also attributed to Antonie van Leeuwenhoek).
Pasteur was responsible for disproving the doctrine of spontaneous generation. Under the auspices of the French Academy of Sciences, his experiment demonstrated that in sterilized and sealed flasks, nothing ever developed; conversely, in sterilized but open flasks, microorganisms could grow. For this experiment, the academy awarded him the Alhumbert Prize carrying 2,500 francs in 1862.
Pasteur is also regarded as one of the fathers of the germ theory of diseases, which was a minor medical concept at the time. His many experiments showed that diseases could be prevented by killing or stopping germs, thereby directly supporting the germ theory and its application in clinical medicine. He is best known to the general public for his invention of the technique of treating milk and wine to stop bacterial contamination, a process now called pasteurization. Pasteur also made significant discoveries in chemistry, most notably on the molecular basis for the asymmetry of certain crystals and racemization. Early in his career, his investigation of sodium ammonium tartrate initiated the field of optical isomerism. This work had a profound effect on structural chemistry, with eventual implications for many areas including medicinal chemistry.
He was the director of the Pasteur Institute, established in 1887, until his death, and his body was interred in a vault beneath the institute. Although Pasteur made groundbreaking experiments, his reputation became associated with various controversies. Historical reassessment of his notebook revealed that he practiced deception to overcome his rivals.
Early life and education
thumb|upright|right|The house in which Pasteur was born, [[Dole, Jura|Dole]]
Louis Pasteur was born on 27 December 1822, in Dole, Jura, France, to a Catholic family of a poor tanner. 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 entered primary school in 1831. He was dyslexic and dysgraphic.
He was an average student in his early years, and not particularly academic, as his interests were fishing and sketching. Pasteur attended secondary school at the Collège d'Arbois. In October 1838, he left for Paris to enroll in a boarding school, but became homesick and returned in November.
In 1839, he entered the at Besançon to study philosophy and earned his Bachelor of Letters degree in 1840. He was appointed a tutor at the Besançon college while continuing a degree science course with special mathematics. He failed his first examination in 1841. He managed to pass the baccalauréat scientifique (general science) degree from Dijon, where he earned his Bachelor of Science in Mathematics degree (Bachelier ès Sciences Mathématiques) in 1842, but with a mediocre grade in chemistry.
Later in 1842, Pasteur took the entrance test for the École Normale Supérieure. During the test, he had to fight fatigue and only felt comfortable with physics and mathematics. He passed the first set of tests, but because his ranking was low, Pasteur decided not to continue and try again next year. He went back to the Parisian boarding school to prepare for the test. He also attended classes at the Lycée Saint-Louis and lectures of Jean-Baptiste Dumas at the Sorbonne. In 1843, he passed the test with a high ranking and entered the École Normale Supérieure. Later, he was a student of Jean-Baptiste Boussingault at the Conservatoire national des arts et métiers. In 1845 he received the degree. In 1846, he was appointed professor of physics at the in Ardèche. But the chemist Antoine Jérôme Balard wanted him back at the École Normale Supérieure as a graduate laboratory assistant (agrégé préparateur). He joined Balard and simultaneously started his research in crystallography and in 1847, he submitted his two theses, one in chemistry and the other in physics: (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 serving briefly as professor of physics at the Dijon Lycée in 1848, he became professor of chemistry at the University of Strasbourg, where he met and courted Marie Laurent, daughter of the university's rector in 1849. They were married on 29 May 1849, and together had five children, only two of whom survived to adulthood; the other three died of typhoid.
Career
thumb|Louis Pasteur, French biologist and chemist, 1878, by A Gerschel
Pasteur was appointed professor of chemistry at the University of Strasbourg in 1848, and became the chair of chemistry in 1852.
In February 1854, so that he would have time to carry out work that could earn him the title of correspondent of the Institute, he got three months' paid leave with the help of a medical certificate of convenience. He extended the leave until 1 August, the date of the start of the exams. "I tell the Minister that I will go and do the examinations so as not to increase the embarrassment of the service. It is also so as not to leave to another a sum of 6 or 700 francs".
In this same year 1854, he was named dean of the new faculty of sciences at University of Lille, where he began his studies on fermentation.
In 1857, he moved to Paris as the director of scientific studies at the École Normale Supérieure where he took control from 1858 to 1867 and introduced a series of reforms to improve the standard of scientific work. The examinations became more rigid, which led to better results, greater competition, and increased prestige. Many of his decrees, however, were rigid and authoritarian, leading to two serious student revolts. During "the bean revolt" he decreed that a mutton stew, which students had refused to eat, would be served and eaten every Monday. On another occasion he threatened to expel any student caught smoking, and 73 of the 80 students in the school resigned.
In 1863, he was appointed professor of geology, physics, and chemistry at the École nationale supérieure des Beaux-Arts, a position he held until his resignation in 1867. In 1867, he became the chair of organic chemistry at the Sorbonne, but he later gave up the position because of poor health. In 1867, the École Normale's laboratory of physiological chemistry was created at Pasteur's request, In Paris, he established the Pasteur Institute in 1887 and served as its director for the rest of his life.
Research
Molecular asymmetry
thumb|Pasteur separated the left and right [[crystal shapes from each other to form two piles of crystals: in solution one form rotated light to the left, the other to the right, while an equal mixture of the two forms canceled each other's effect, and does not rotate the polarized light.]]
In Pasteur's early work as a chemist, beginning at the École Normale Supérieure, and continuing at Strasbourg and Lille, he examined the chemical, optical and crystallographic properties of a group of compounds known as tartrates. A solution of this compound derived from living things rotated the plane of polarization of light passing through it. The problem was that tartaric acid derived by chemical synthesis had no such effect, even though its chemical reactions were identical and its elemental composition was the same. The (2R,3R)- and (2S,3S)- tartrates were isometric, non-superposable mirror images of each other. This was the first time anyone had demonstrated molecular chirality, and also the first explanation of isomerism. A memoire was subsequently published on 30 November 1857. In the memoir, he developed his ideas stating that: "I intend to establish that, just as there is an alcoholic ferment, the yeast of beer, which is found everywhere that sugar is decomposed into alcohol and carbonic acid, so also there is a particular ferment, a lactic yeast, always present when sugar becomes lactic acid."
This memoir on alcoholic fermentation was published in full form in 1858. Jöns Jacob Berzelius and Justus von Liebig had proposed the theory that fermentation was caused by decomposition. Pasteur demonstrated that this theory was incorrect, and that yeast was responsible for fermentation to produce alcohol from sugar. He also demonstrated that, when a different microorganism contaminated the wine, lactic acid was produced, making the wine sour.
thumb|left|Pasteur experimenting in his laboratory
thumb|[[Institut Pasteur de Lille]]
Pasteur's research also showed that the growth of micro-organisms was responsible for spoiling beverages, such as beer, wine and milk. With this established, he invented a process in which liquids such as milk were heated to a temperature between 60 and 100 °C. Pasteur patented the process, to fight the "diseases" of wine, in 1865. The method became known as pasteurization, and was soon applied to beer and milk.
Beverage contamination led Pasteur to the idea that micro-organisms infecting animals and humans cause disease. He proposed preventing the entry of micro-organisms into the human body, leading Joseph Lister to develop antiseptic methods in surgery.
In 1866, Pasteur published Études sur le Vin, about the diseases of wine, and he published Études sur la Bière in 1876, concerning the diseases of beer.
Silkworms with pébrine were covered in corpuscles. In the first three years, Pasteur thought that the corpuscles were a symptom of the disease. In 1870, he concluded that the corpuscles were the cause of pébrine (it is now known that the cause is a microsporidian). Pasteur also showed that the disease was hereditary. Pasteur developed a system to prevent pébrine: after the female moths laid their eggs, the moths were turned into a pulp. The pulp was examined with a microscope, and if corpuscles were observed, the eggs were destroyed.
Spontaneous generation
thumb|Bottle en col de cygne ([[swan neck flask|swan-neck bottle) used by Pasteur]]
thumb|Louis Pasteur's pasteurization experiment illustrates the fact that the spoilage of liquid was caused by particles in the air rather than the air itself. These experiments were important pieces of evidence supporting the germ theory of disease.
Following his fermentation experiments, Pasteur demonstrated that the skin of grapes was the natural source of yeasts, and that sterilized grapes and grape juice never fermented. He drew grape juice from under the skin with sterilized needles, and also covered grapes with sterilized cloth. Both experiments could not produce wine in sterilized containers.
Pouchet stated that air everywhere could cause spontaneous generation of living organisms in liquids. In the late 1850s, he performed experiments and claimed that they were evidence of spontaneous generation. Pasteur also used swan neck flasks containing a fermentable liquid. Air was allowed to enter the flask via a long curving tube that made dust particles stick to it. Nothing grew in the broths unless the flasks were tilted, making the liquid touch the contaminated walls of the neck. This showed that the living organisms that grew in such broths came from outside, on dust, rather than spontaneously generating within the liquid or from the action of pure air.
These were some of the most important experiments disproving the theory of spontaneous generation. Pasteur gave a series of five presentations of his findings before the French Academy of Sciences in 1881, which were 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 Existing in the Atmosphere: Examining the Doctrine of Spontaneous Generation). Pasteur won the Alhumbert Prize in 1862. He concluded that:
In fact, Pasteur's vaccine against chicken cholera did not consistently produce immunity, and has subsequently been proven to be ineffective.
Anthrax
Following the results with chicken cholera, Pasteur eventually utilized the immunization method developed for chicken cholera to create a vaccine for anthrax, which affected cattle. In 1877, Pasteur had earlier directed his laboratory to culture the bacteria from the blood of infected animals, following the discovery of the bacterium by Robert Koch. Many cattle were dying of anthrax in "cursed fields".
Pasteur's interest in creating a vaccine for anthrax was greatly stimulated when on 12 July 1880, Henri Bouley read before the French Academy of Sciences a report from Henry Toussaint, a veterinary surgeon, who was not a member of the academy. Toussaint had developed anthrax vaccine by killing the bacilli by heating at 55 °C for 10 minutes. He tested his vaccine on eight dogs and 11 sheep, half of which died after inoculation. It was not a great success. Upon hearing the news, Pasteur immediately wrote to the academy that he could not believe that dead vaccine would work and that Toussaint's claim "overturns all the ideas I had on viruses, vaccines, etc."
However, Pasteur's laboratory found that anthrax bacillus was not easily weakened by culturing in air as it formed spores – unlike chicken cholera bacillus. In early 1881, his laboratory discovered that growing anthrax bacilli at about 42 °C made them unable to produce spores, and he described this method in a speech to the French Academy of Sciences on 28 February. On 21 March, despite inconsistent results, he announced successful vaccination of sheep. To this news, veterinarian Hippolyte Rossignol proposed that the Société d'agriculture de Melun organize an experiment to test Pasteur's vaccine. Pasteur signed an agreement accepting the challenge on 28 April. Pasteur's assistants, Roux and Chamberland, who were assigned the task of conducting the trial, were concerned about the unreliability of the attenuated vaccine, and therefore Chamberland secretly prepared an alternative vaccine using chemical inactivation. On 31 May, Roux and Chamberland next injected the animals with the fresh virulent culture of anthrax bacillus. The official result was observed and analyzed on 2 June in the presence of over 200 spectators, with Pasteur himself in attendance. The results were as Pasteur had bravely predicted: "I hypothesized that the six vaccinated cows would not become very ill, while the four unvaccinated cows would perish or at least become very ill." His report to the French Academy of Sciences on 13 June concludes: