Pasteur, Louis (1822-95), world-renowned 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 27, 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
polarized light was passed through a solution of artificially synthesized
organic nutrients, no rotation took place. If, however, bacteria or other
microorganisms 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
mirror images of each other), which he referred to as "left-handed" and
"right-handed" forms. When chemists synthesize an organic compound, both of
these forms are produced in equal proportions, canceling 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 beverages. 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 starting sugar solutions to
a high temperature.
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 microorganisms 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 Académie des Sciences officially accepted Pasteur's results in 1864,
gave great impetus to improving experimental techniques in microbiology.
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 microorganisms invade milk and cause
fermentation. This concept, called the germ theory of disease, was strongly
debated by physicians 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 skeptical 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 septicemia, cholera, diphtheria, 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 centers 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 treatment.
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
centers in the world for the study of infectious diseases and other
subjects related to microorganisms, including molecular genetics.) By the
time of his death in Saint-Cloud on September 28, 1895, Pasteur had long
since become a national hero and had been honored in many ways. He was
given a state funeral at the Cathedral of Nôtre Dame, and his body was
placed in a permanent crypt in his institute.
"Pasteur, Louis," Microsoft(R) Encarta(R) 98 Encyclopedia. (c) 1993-1997
Microsoft Corporation. All rights reserved.
Other Links of interest
Pasteur Institute
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