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Summary Article: Pasteur, Louis (1822-1895)
From The Hutchinson Dictionary of Scientific Biography

Place: France

Subject: biography, biology

French chemist and microbiologist who became world famous for originating the process of pasteurization and for establishing the validity of the germ theory of disease, although he also made many other scientific contributions. Regarded as one of the greatest scientists in history, he received many honours during his lifetime, including the Legion of Honour, France's highest award.

Pasteur was born on 27 December 1822 in Dôle in eastern France, the son of a tanner. While he was still young, his family moved to Arbois, where he attended primary and secondary schools. He was not a particularly good student, but he showed an aptitude for painting and mathematics and his initial ambition was to become a professor of fine arts. He continued his education at the Royal College in Besançon, from which he gained his BA in 1840 and his BSc in 1842. In 1843 Pasteur entered the Ecole Normale Supérieure in Paris, where he began to study chemistry and from which he gained his doctorate in 1847. In the following year he was appointed professor of physics at the Dijon Lycée but shortly afterwards, early in 1849, he accepted the post of professor of chemistry at the University of Strasbourg. In the same year he married Marie Laurent, the daughter of the university's rector; later they had five children, only two of whom survived beyond childhood. In 1862 Pasteur was elected to the French Academy of Sciences, and in 1863 to a chair at the Ecole Normale Supérieure, a position that was created for him so that he could institute an original teaching programme that related chemistry, physics, and geology to the fine arts. Also in 1863 he became dean of the new science faculty at Lille University, where he initiated the novel concept of evening classes for workers. Meanwhile, in 1857 he had been appointed director of scientific studies at the Ecole Normale Supérieure. Because of the pressure of his research work, Pasteur resigned from the directorship in 1867 but, with financial assistance from Emperor Napoleon III, a laboratory of physiological chemistry was established for him at the Ecole. Pasteur suffered a stroke in 1868 but, although partly paralysed, continued his work. In 1873 he was made a member of the French Academy of Medicine, and in the following year the French parliament granted him a special monetary award to guarantee his financial security while he pursued his research. In 1882 he was elected to the Academic Française. In 1888 the Pasteur Institute was created in Paris for the purpose of continuing Pasteur's pioneering research into rabies; he headed this establishment until his death, in Paris, on 28 September 1895.

Pasteur first gained recognition through his early work on the optical activity of stereoisomers. In 1848 he presented a paper to the Paris Academy of Sciences in which he reported that there are two molecular forms of tartaric acid: one that rotates plane polarized light to the right and another (a mirror image of the first) that rotates it to the left. In addition, he showed that one form can be assimilated by living micro-organisms whereas its optical antipode cannot.

Pasteur began his biological investigations - for which he is best known - while at Lille University. After receiving a query from an industrialist about wine- and beermaking, Pasteur started researching the process of fermentation. Using a microscope he found that properly aged wine contains small spherical globules of yeast cells whereas sour wine contains elongated yeast cells. He also proved that fermentation does not require oxygen, but that it nevertheless involves living micro-organisms and that to produce the correct type of fermentation (alcohol-producing rather than lactic-acid-producing) it is necessary to use the correct type of yeast. Pasteur also realized that after wine has formed, it should be gently heated to about 50°C/122°F to kill the yeast and thereby prevent souring during the ageing process. Pasteurization - as this heating process is called today - is now widely used in the food-processing industry.

Pasteur then turned his attention to spontaneous generation, a problem that had once again become a matter of controversy, despite Lazzaro Spallanzani's disproof of the theory about a century previously. Pasteur showed that dust in the air contains spores of living organisms, which reproduce when introduced into a nutrient broth. Then he boiled the broth in a container with a U-shaped tube that allowed air to reach the broth but trapped dust in the U-bend. He found that the broth remained free of living organisms, thereby again disproving the theory of spontaneous generation.

In the mid-1860s the French silk industry was seriously threatened by a disease that killed silkworms and Pasteur was commissioned by the government to investigate the disease. In 1868 he announced that he had found a minute parasite that infects the silkworms, and recommended that all infected silkworms be destroyed. His advice was followed and the disease eliminated. This stimulated his interest in infectious diseases and, from the results of his previous work on fermentation, spontaneous generation, and the silkworm disease, Pasteur developed the germ theory of disease. This theory was probably the most important single medical discovery of all time, because it provided both a practical method of combating disease by disinfection and a theoretical foundation for further research.

Continuing his research into disease, in 1881 Pasteur developed a method for reducing the virulence of certain pathogenic micro-organisms. By heating a preparation of anthrax bacilli he attenuated their virulence but found that they still brought about the full immune response when injected into sheep. Using a similar method, Pasteur then inoculated fowl against chicken cholera. He was thus following the work of Edward Jenner, who had first vaccinated against cowpox in 1796. In 1882 Pasteur began what proved to be his most spectacular research: the prevention of rabies. He demonstrated that the causative micro-organism (actually a virus, although their existence was not known at that time) infects the nervous system and then, using the dried tissues of infected animals, he eventually succeeded in obtaining an attenuated form of the virus suitable for the inoculation of human beings. The culmination of this work came on 6 July 1885, when Pasteur used his vaccine to save the life of a young boy who had been bitten by a rabid dog. The success of this experiment brought Pasteur even greater acclaim and led to the establishment of the Pasteur Institute in 1888.

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