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Pasteur, Louis (1822-1895), French chemist and biologist, who founded the science of microbiology, proved the germ theory of disease, invented the process of pasteurization, and developed vaccines for several diseases, including rabies. Pasteur was born in Dôle on December 7, 1822, the son of a tanner, and grew up in the small town of Arbois. In 1847, he earned a doctorate at the École Normale in Paris, with a focus on both physics and chemistry.

Pasteur, Louis (1822-1895), French chemist and biologist, who founded
the science of microbiology, proved the germ theory of disease,
invented the process of pasteurization, and developed vaccines for
several diseases, including rabies.

Pasteur was born in Dôle on December 7, 1822, the son of a tanner, and
grew up in the small town of Arbois. In 1847, he earned a doctorate at
the École Normale in Paris, with a focus on both physics and
chemistry. Becoming an assistant to one of his teachers, he began
research that led to a significant discovery. He found that a beam of
polarized light (see Optics) was rotated to either the right or the
left as it passed through a pure solution of naturally produced
organic nutrients, whereas when such a beam was passed through a
solution of artificially synthesized organic nutrients, no rotation
took place. If, however, bacteria or other micro-organisms were placed
in the latter solution, after a while it would also rotate light to
the right or left.

Pasteur concluded that organic molecules can exist in one of two
forms, called isomers (that is, having the same structure and
differing only in being mirror images of each other), which he
referred to as "left-handed" and "right-handed" forms. When chemists
synthesize an organic compound, these forms are produced in equal
proportions, cancelling each other's optical effects. Living systems,
however, which have a high degree of chemical specificity, can
discriminate between the two forms, metabolizing one and leaving the
other untouched and free to rotate light.

Work on Fermentation

After spending several years of research and teaching at Dijon and
Strasbourg, Pasteur moved in 1854 to the University of Lille, where he
was named Professor of Chemistry and dean of the faculty of sciences.
This faculty had been set up partly to serve as a means of applying
science to the practical problems of the industries of the region,
especially the manufacture of alcoholic drinks. Pasteur immediately
devoted himself to research on the process of fermentation. Although
his belief that yeast plays some kind of role in this process was not
original, he was able to demonstrate, from his earlier work on
chemical specificity, that the desired production of alcohol in
fermentation is indeed due to yeast and that the undesired production
of substances (such as lactic acid or acetic acid) that make wine sour
is due to the presence of additional organisms, such as bacteria. The
souring of wine and beer had been a major economic problem in France;
Pasteur contributed to solving the problem by showing that bacteria
can be eliminated by heating the initial sugar solutions to a high

Pasteur extended these studies to such other problems as the souring
of milk, and he proposed a similar solution: heating the milk to a
high temperature and pressure before bottling. This process is now
called pasteurization.

Disproof of Spontaneous Generation

Fully aware of the presence of micro-organisms in nature, Pasteur
undertook several experiments designed to address the question of
where these "germs" came from. Were they spontaneously produced in
substances themselves, or were they introduced into substances from
the environment? Pasteur concluded that the latter was always the
case. His findings resulted in a fierce debate with the French
biologist Félix Pouchet--and later with the noted English
bacteriologist Henry Bastion--who maintained that under appropriate
conditions instances of spontaneous generation could be found. These
debates, which lasted well into the 1870s, although a commission of
the Academy of Sciences officially accepted Pasteur's results in 1864,
gave great impetus to improving experimental techniques in

Silkworm Studies

In 1865 Pasteur was summoned from Paris, where he had become
administrator and director of scientific studies at the École Normale,
to come to the aid of the silk industry in southern France. The
country's enormous production of silk had suddenly been curtailed
because a disease of silkworms, known as pébrine, had reached epidemic
proportions. Suspecting that certain microscopic objects found in the
diseased silkworms (and in the moths and their eggs) were
disease-producing organisms, Pasteur experimented with controlled
breeding and proved that pébrine was not only contagious but also
hereditary. He concluded that only in diseased and living eggs was the
cause of the disease maintained; therefore, selection of disease-free
eggs was the solution. By adopting this method of selection, the silk
industry was saved from disaster.

Germ Theory of Disease

Pasteur's work on fermentation and spontaneous generation had
considerable implications for medicine, because he believed that the
origin and development of disease are analogous to the origin and
process of fermentation. That is, disease arises from germs attacking
the body from outside, just as unwanted micro-organisms invade milk
and cause fermentation. This concept, called the germ theory of
disease, was strongly debated by doctors and scientists around the
world. One of the main arguments against it was the contention that
the role germs played during the course of disease was secondary and
unimportant; the notion that tiny organisms could kill vastly larger
ones seemed ridiculous to many people. Pasteur's studies convinced him
that he was right, however, and in the course of his career he
extended the germ theory to explain the causes of many diseases.

Anthrax Research

Pasteur also determined the natural history of anthrax, a fatal
disease of cattle. He proved that anthrax is caused by a particular
bacillus and suggested that animals could be given anthrax in a mild
form by vaccinating them with attenuated (weakened) bacilli, thus
providing immunity from potentially fatal attacks. In order to prove
his theory, Pasteur began by inoculating 25 sheep; a few days later he
inoculated these and 25 more sheep with an especially strong
inoculant, and he left 10 sheep untreated. He predicted that the
second 25 sheep would all perish and concluded the experiment
dramatically by showing, to a sceptical crowd, the carcasses of the 25
sheep lying side by side.

Rabies Vaccine

Pasteur spent the rest of his life working on the causes of various
diseases--including septicaemia, cholera, diptheria, fowl cholera,
tuberculosis, and smallpox--and their prevention by means of
vaccination. He is best known for his investigations concerning the
prevention of rabies, otherwise known in humans as hydrophobia. After
experimenting with the saliva of animals suffering from this disease,
Pasteur concluded that the disease rests in the nerve centres of the
body; when an extract from the spinal column of a rabid dog was
injected into the bodies of healthy animals, symptoms of rabies were
produced. By studying the tissues of infected animals, particularly
rabbits, Pasteur was able to develop an attenuated form of the virus
that could be used for inoculation.

In 1885 a young boy and his mother arrived at Pasteur's laboratory;
the boy had been bitten badly by a rabid dog, and Pasteur was urged to
treat him with his new method. At the end of the treatment, which
lasted ten days, the boy was being inoculated with the most potent
rabies virus known; he recovered and remained healthy. Since that
time, thousands of people have been saved from rabies by this

Pasteur's research on rabies resulted, in 1888, in the founding of a
special institute in Paris for the treatment of the disease. This
became known as the Institut Pasteur, and it was directed by Pasteur
himself until he died. (The institute still flourishes and is one of
the most important centres in the world for the study of infectious
diseases and other subjects related to micro-organisms, including
molecular genetics.) By the time of his death in St-Cloud on September
28, 1895, Pasteur had long been a national hero and had been honoured
in many ways. He was given a state funeral at the cathedral of Notre
Dame, and his body was placed in a permanent crypt in his institute.

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"Pasteur, Louis," Microsoft® Encarta® 98 Encyclopedia. © 1993-1997
Microsoft Corporation. All rights reserved.

Mendeleyev, Dimity Ivanovich (1834-1907), Russian chemist, best known
for his development of the periodic table of the properties of the
chemical elements. This table displays a periodicity (regular pattern)
in the elements' properties when they are arranged according to atomic


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