Louis Pasteur

Early life and education

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. He drew many pastels and portraits of his parents, friends and neighbors. 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 Collège Royal 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 licencié ès sciences  degree. In 1846, he was appointed professor of physics at the Collège de Tournon 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

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. It was on this occasion that Pasteur uttered his oft-quoted remark: "dans les champs de l'observation, le hasard ne favorise que les esprits préparés" ("In the field of observation, chance favors only the prepared mind").

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, and he was the laboratory's director from 1867 to 1888. In Paris, he established the Pasteur Institute in 1887 and served as its director for the rest of his life.

Research

Molecular asymmetry

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.

He resolved a problem concerning the nature of tartaric acid in 1848. 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.

Pasteur noticed that crystals of tartrates had small faces. Then he observed that, in racemic mixtures of tartrates, half of the crystals were right-handed and half were left-handed. In solution, the right-handed compound was dextrorotatory, and the left-handed one was levorotatory. Pasteur determined that optical activity related to the shape of the crystals, and that an asymmetric internal arrangement of the molecules of the compound was responsible for twisting the light. 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.

Some historians consider Pasteur's work in this area to be his "most profound and most original contributions to science", and his "greatest scientific discovery."

Fermentation and germ theory of diseases

Pasteur was motivated to investigate fermentation while working at Lille. In 1856 a local wine manufacturer, M. Bigot, whose son was one of Pasteur's students, sought for his advice on the problems of making beetroot alcohol and souring. Pasteur began his research in the topic by repeating and confirming works of Theodor Schwann, who demonstrated a decade earlier that yeast were alive.

According to his son-in-law, René Vallery-Radot, in August 1857 Pasteur sent a paper about lactic acid fermentation to the Société des Sciences de Lille, but the paper was read three months later. 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. In 1861, Pasteur observed that less sugar fermented per part of yeast when the yeast was exposed to air. The lower rate of fermentation aerobically became known as the Pasteur effect.

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 (140 and 212 °F). This killed most bacteria and moulds already present within them. Pasteur and Claude Bernard completed tests on blood and urine on 20 April 1862. 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.

In the early 19th century, Agostino Bassi had shown that muscardine was caused by a fungus that infected silkworms. Since 1853, two diseases called pébrine and flacherie had been infecting great numbers of silkworms in southern France, and by 1865 they were causing huge losses to farmers. In 1865, Pasteur went to Alès and worked for five years until 1870.

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. Pasteur concluded that bacteria caused flacherie. The primary cause is currently thought to be viruses. The spread of flacherie could be accidental or hereditary. Hygiene could be used to prevent accidental flacherie. Moths whose digestive cavities did not contain the microorganisms causing flacherie were used to lay eggs, preventing hereditary flacherie.

Spontaneous generation

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.

His findings and ideas were against the prevailing notion of spontaneous generation. He received a particularly stern criticism from Félix Archimède Pouchet, who was director of the Rouen Museum of Natural History. To settle the debate between the eminent scientists, the French Academy of Sciences offered the Alhumbert Prize carrying 2,500 francs to whoever could experimentally demonstrate for or against the doctrine.

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. Francesco Redi and Lazzaro Spallanzani had provided some evidence against spontaneous generation in the 17th and 18th centuries, respectively. Spallanzani's experiments in 1765 suggested that air contaminated broths with bacteria. In the 1860s, Pasteur repeated Spallanzani's experiments, but Pouchet reported a different result using a different broth.