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Louis Pasteur
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Louis Pasteur

Louis Pasteur (December 27 1822September 28 1895) was a French microbiologist and chemist who advocated the germ theory of disease and developed techniques of inoculation.

Louis Pasteur was born in Dole, Jura département, France, the son of a tanner. He was admitted in 1843 at the École Normale Supérieure in Paris and got a doctoral degree in 1846. He studied chemistry, but showed little promise at first (one of his professors described him as "mediocre"). Nevertheless, he became a scientist.

In his early work as a chemist he resolved a problem concerning the nature of tartaric acid (1849). A solution of this compound derived from one source rotated the plane of polarization of light passing through it. The mystery was that tartaric acid derived by synthesis had no such effect, even though its reactions were identical and its composition was the same.

Pasteur noticed, upon examination of the tiny crystals of tartaric acid, 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 tartaric acid: solutions of one form rotated polarised light clockwise, while the other form rotated light anticlockwise. An equal mix of the two had no effect on polarized light. Pasteur correctly deduced that the tartaric acid molecule was asymmetric and could exist in two different forms that resemble one another as a left- and right-hand glove resemble one another. 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.

His doctoral thesis on crystallography got him 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 1857, he was made administrator and director of scientific studies of the École Normale Supérieure.

He demonstrated that fermentation was caused by the growth of microorganisms, and that the growth of microorganisms in nutrient broths was not due to spontaneous generation. He exposed freshly 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 being spontaneously generated within the broth. Thus, Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory.

Louis Pasteur did not develop germ theory; Girolamo Fracastoro, Friedrich Henle and others suggested it earlier. Pasteur conducted experiments that clearly indicated its correctness and managed to convince most of Europe that it was true.

Pasteur's research also showed that some microorganisms contaminated the fermenting beverages. With this established, he invented the process of pasteurization, in which liquids such as milk were heated to kill all bacteria and molds already present within them. He and Claude Bernard completed the first pasteurization test on April 20, 1862.

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, Pasteur set out to help the silk industry. A disease called pebrine was killing great numbers of silkworms. He worked several years to prove that a microbe that attacks silkworm eggs causes the disease, and that eliminating this microbe in silkworm nurseries would wipe out the disease.

His 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, although they had not actually caused the disease. In the 1870s he applied this immunization method to anthrax, which affected cattle, and aroused interest in combating other diseases.

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 than with the naturally acquired disease. Edward Jenner had also discovered vaccination, using cowpox to give cross-immunity to smallpox, and by Pasteur's time this had generally replaced the use of actual smallpox material in inoculation. The difference with chicken cholera and anthrax was that the weakened form of the disease organism 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, which 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. Fortunately, the treatment proved to be a spectacular success, with Meister avoiding the disease. So 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.

Pasteur also discovered anaerobiosis - that some microorganisms can develop and live without air or oxygen.

He won the Leeuwenhoek medal, microbiology's highest honor, in 1895.

Pasteur died in 1895 near Paris from complications caused by a series of strokes that had begun plaguing him as far back as 1868. He was buried in the Cathedral of Notre Dame, but his remains were soon placed in a crypt in the Institut Pasteur, Paris.

Pasteur's method of immunization was effective and was employed by many other physicians, leading to the eradication of the diseases typhus and polio as threats. Pasteurization led to the elimination of contaminated milk and other drinks as sources of disease. In fact, Pasteur inaugurated the modern age of medicine, leading to an increase in the human life span in much of the (wealthy) world and a surprising population explosion. Accordingly, he has been hailed as the "Father of Medicine" and a "Benefactor of Humanity."


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