- Category : Chemist
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Louis Pasteur (December 27, 1822 – September 28, 1895) was a French chemist best known for his remarkable breakthroughs in microbiology.
His experiments confirmed the germ theory of disease, also reducing mortality from puerperal fever (childbed), and he created the first vaccine for rabies.
He is best known to the general public for showing how to stop milk and wine from going sour - this process came to be called pasteurization. He is regarded as one of the three main founders of bacteriology, together with Ferdinand Cohn and Robert Koch. He also made many discoveries in the field of chemistry, most notably the asymmetry of crystals.
Early life and biography
Louis Jean Pasteur was born on December 27, 1822 in Dole in the Jura region of France and grew up in the town of Arbois. There he later had his house and laboratory, which is a Pasteur museum today. His father, Jean Pasteur, was a tanner and a veteran of the Napoleonic wars. Louis's aptitude was recognized by his college headmaster, who recommended that the young man apply for the École Normale Supérieure, which accepted him. After serving briefly as professor of physics at Dijon Lycée in 1848, he became professor of chemistry at Strasbourg University, where he met and courted Marie Laurent, daughter of the university's rector in 1849. They were married on May 29, 1849 and together they had five children, only two of whom survived to adulthood. Throughout his whole life, Louis Pasteur remained an ardent Catholic. A well-known quotation illustrating this is attributed to him: "I have the faith of a Breton peasant, and by the time I die I hope to have the faith of a Breton peasant's wife."
Work on chirality and the polarization of light
In Pasteur's early works as a chemist, he resolved a problem concerning the nature of tartaric acid (1849). A solution of this compound derived from living things (specifically, wine lees) rotated the plane of polarization of light passing through it. The mystery was that tartaric acid derived by chemical synthesis had no such effect, even though its reactions were identical and its elemental composition was the same.
Upon examination of the minuscule crystals of Sodium ammonium tartrate, Pasteur noticed that the crystals came in two asymmetric forms that were mirror images of one another. Tediously sorting the crystals by hand gave two forms of the compound: solutions of one form rotated polarized light clockwise, while the other form rotated light counterclockwise. An equal mix of the two had no polarizing effect on light. Pasteur correctly deduced the molecule in question was asymmetric and could exist in two different forms that resemble one another as would left- and right-hand gloves, and that the organic form of the compound consisted purely of the one type. As the first demonstration of chiral molecules, it was quite an achievement, but Pasteur then went on to his more famous work in the field of biology/medicine.
Pasteur's doctoral thesis on crystallography attracted the attention of M. Puillet and he helped him garner a position of professor of chemistry at the Faculté (College) of Strasbourg.
In 1854, he was named Dean of the new College of Science in Lille. In 1856, he was made administrator and director of scientific studies of the École Normale Supérieure.
Louis Pasteur demonstrated that the fermentation process is caused by the growth of microorganisms, and that the growth of microorganisms in nutrient broths is not due to spontaneous generation.
He exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium, and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass. Nothing grew in the broths; therefore, the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory.
While Pasteur was not the first to propose germ theory (Girolamo Fracastoro, Agostino Bassi, Friedrich Henle and others had suggested it earlier), he developed it and conducted experiments that clearly indicated its correctness and managed to convince most of Europe it was true. Today he is often regarded as the father of germ theory and bacteriology, together with Robert Koch.
Pasteur's research also showed that some microorganisms contaminated fermenting beverages. With this established, he invented a process in which liquids such as milk were heated to kill most bacteria and molds already present within them. He and Claude Bernard completed the first test on April 20, 1862. This process was soon afterwards known as pasteurisation (or "pasteurization" in America).
Beverage contamination led Pasteur to conclude that microorganisms infected animals and humans as well. He proposed preventing the entry of microorganisms into the human body, leading Joseph Lister to develop antiseptic methods in surgery.
In 1865, two parasitic diseases called pébrine and flacherie were killing great numbers of silkworms at Alès. Pasteur worked several years proving it was a microbe attacking silkworm eggs which caused the disease, and that eliminating this microbe within silkworm nurseries would eradicate the disease.
Pasteur also discovered anaerobiosis, whereby some microorganisms can develop and live without air or oxygen.
Immunology and Vaccination
Pasteur's later work on diseases included work on chicken cholera. During this work, a culture of the responsible bacteria had spoiled and failed to induce the disease in some chickens he was infecting with the disease. Upon reusing these healthy chickens, Pasteur discovered that he could not infect them, even with fresh bacteria; the weakened bacteria had caused the chickens to become immune to the disease, even though they had only caused mild symptoms.
This discovery was serendipitous. His assistant Charles Chamberland (of French origin) had been instructed to inoculate the chickens after Pasteur went on holiday. Chamberland failed to do this, but instead went on holiday himself. On his return, the month old cultures made the chickens unwell, but instead of the infection being fatal, as usual, the chickens recovered completely. Chamberland assumed an error had been made, and wanted to discard the apparently faulty culture when Pasteur stopped him. Pasteur guessed the recovered animals now might be immune to the disease, as were the animals at Eure-et-Loir that had recovered from anthrax.
In the 1870s, he applied this immunisation method to anthrax, which affected cattle, and aroused interest in combating other diseases.
Pasteur publicly claimed he had made the anthrax vaccine by exposing the bacillus to oxygen. His laboratory notebooks, now in the Bibliotheque Nationale in Paris, in fact show Pasteur used the method of rival Jean-Joseph-Henri Toussaint, a Toulouse veterinary surgeon, to create the anthrax vaccine. This method used the oxidizing agent potassium dichromate. Pasteur's oxygen method did eventually produce a vaccine but only after he had been awarded a patent on the production of an anthrax vaccine.
The notion of a weak form of a disease causing immunity to the virulent version was not new; this had been known for a long time for smallpox. Inoculation with smallpox was known to result in far less scarring, and greatly reduced mortality, in comparison to the naturally acquired disease. Edward Jenner had also discovered vaccination, using cowpox to give cross-immunity to smallpox (in 1796), and by Pasteur's time this had generally replaced the use of actual smallpox material in inoculation. The difference between smallpox vaccination and cholera and anthrax vaccination was that the weakened form of the latter two disease organisms had been generated artificially, and so a naturally weak form of the disease organism did not need to be found.
This discovery revolutionised work in infectious diseases, and Pasteur gave these artificially weakened diseases the generic name of vaccines, to honour Jenner's discovery. Pasteur produced the first vaccine for rabies by growing the virus in rabbits, and then weakening it by drying the affected nerve tissue.
The rabies vaccine was initially created by Emile Roux, a French doctor and a colleague of Pasteur who had been working with a killed vaccine produced by desiccating the spinal cords of infected rabbits. The vaccine had only been tested on eleven dogs before its first human trial.
This vaccine was first used on 9-year old Joseph Meister, on July 6, 1885, after the boy was badly mauled by a rabid dog. This was done at some personal risk for Pasteur, since he was not a licensed physician and could have faced prosecution for treating the boy. However, left without treatment, the boy faced almost certain death from rabies. After consulting with colleagues, Pasteur decided to go ahead with the treatment. Fortunately, the treatment proved to be a spectacular success, with Meister avoiding the disease; thus, Pasteur was hailed as a hero and the legal matter was not pursued. The treatment's success laid the foundations for the manufacture of many other vaccines. The first of the Pasteur Institutes was also built on the basis of this achievement.
Honors and final days
Pasteur won the Leeuwenhoek medal, microbiology's highest honor, in 1895.
He was Grande Croix of the Legion of Honor.
He died in 1895, near Paris, from complications of a series of strokes that had started in 1868. He died while listening to the story of St Vincent de Paul, whom he admired and sought to emulate. He was buried in the Cathedral of Notre Dame, but his remains were reinterred in a crypt in the Institut Pasteur, Paris where he is remembered for his life-saving work.
Both Institut Pasteur and Université Louis Pasteur were named after him.