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Louis Pasteur was born on December 27, 1822 in Dole, in the region of Jura, France. His
discovery that most infectious diseases are caused by germs, known as the “germ theory of
disease”, is one of the most important in medical history. His work became the foundation for the
science of microbiology, and a cornerstone of modern medicine.
Pasteur’s phenomenal contributions to microbiology and medicine can be summarized as follows.
First, he championed changes in hospital practices to minimize the spread of disease by microbes.
Second, he discovered that weakened forms of a microbe could be used as an immunization
against more virulent forms of the microbe. Third, Pasteur found that rabies was transmitted by
agents so small they could not be seen under a microscope, thus revealing the world of viruses. As
a result he developed techniques to vaccinate dogs against rabies, and to treat humans bitten by
rabid dogs. And fourth, Pasteur developed “pasteurization”, a process by which harmful microbes
in perishable food products are destroyed using heat, without destroying the food.
Each discovery in the body of Pasteur’s work represents a link in an uninterrupted chain,
beginning with molecular asymmetry and ending with his rabies prophylaxis, by way of his
research in fermentation, silkworm, wine and beer diseases, asepsis and vaccines.
From Crystallography to Molecular Asymmetry
In 1847 at the age of 26, Pasteur did his first work on molecular asymmetry, bringing together the
principles of crystallography, chemistry and optics. He formulated a fundamental law: asymmetry
differentiates the organic world from the mineral world. In other words, asymmetric molecules are
always the product of life forces. His work became the basis of a new science — stereochemistry.
Research on Fermentation and Spontaneous Generation
At the request of a distiller named Bigo from the north of France, Pasteur began to examine why
alcohol becomes contaminated with undesirable substances during fermentation. He soon
demonstrated that each sort of fermentation is linked to the existence of a specific microorganism
or ferment — a living being that one can study by cultivation in an appropriate, sterile medium.
This insight is the basis of microbiology.
Pasteur delivered the fatal blow to the doctrine of spontaneous generation, the theory held for 20
centuries that life could arise spontaneously in organic materials. He also developed a germ
theory. At the same time, he discovered the existence of life without oxygen: “Fermentation is the
consequence of life without air”. The discovery of anaerobic life paved the way for the study of
germs that cause septicemia and gangrene, among other infections. Thanks to Pasteur, it became
possible to devise techniques to kill microbes and to control contamination.
Technique of “Pasteurization”
Emperor Napoleon III asked Pasteur to investigate the diseases afflicting wine which were
causing considerable economic losses to the wine industry. Pasteur went to a vineyard in Arbois in
1864 to study this problem. He demonstrated that wine diseases are caused by microorganisms
that can be killed by heating the wine to 55deg.C for several minutes. Applied to beer and milk,
this process, called “pasteurization”, soon came into use throughout the world.
Research on Infectious Diseases Afflicting Man and Animal
In 1865, Pasteur began to study the silkworm diseases that were crippling the silk industry in
France. He discovered the infectious agents and revealed the manner in which these agents are
transmitted–by contagion and hereditary principle — and how to prevent them. Elaborating on his
study of fermentation, he could now confirm that each disease is caused by a specific microbe and
that these microbes are foreign elements. With this knowledge, Pasteur was able to establish the
basic rules of sterilization or asepsis. Preventing contagion and infection, his method of
sterilization revolutionized surgery and obstetrics.
From 1877 to 1887, Pasteur employed these fundamentals of microbiology in the battle against
infectious diseases. He went on to discover three bacteria responsible for human illnesses :
staphylococcus, streptococcus and pneumococcus.
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