Pasteur Begins Developing Germ Theory and Microbiology

Louis Pasteur demonstrated not only that specific living organisms are required for fermentation but also that the process itself is biological. Similarly, the presence of microorganisms in silkworms resulted in the disease pébrine. Pasteur applied a similar principle of microorganisms as the etiological agents of animal diseases in what became known as the germ theory of disease.

Summary of Event

Louis Pasteur was initially trained as an educator at the École Normale Supérieure in Paris but entered the science section in 1844. He received his doctorate in physics and chemistry there in 1847. More interested in science than a career in education, Pasteur was appointed professor of physics at the lycee in Dijon in 1848. He finally found a home in 1857, when he became director of scientific studies at the École Normale Supérieure. As a member until 1867, it was here that Pasteur carried out much of the significant work in his early career. Germ theory
Medicine;germ theory
Pasteur, Louis
Diseases;and germ theory[Germ theory]
Biology;germ theory
[kw]Pasteur Begins Developing Germ Theory and Microbiology (1857)
[kw]Begins Developing Germ Theory and Microbiology, Pasteur (1857)
[kw]Developing Germ Theory and Microbiology, Pasteur Begins (1857)
[kw]Germ Theory and Microbiology, Pasteur Begins Developing (1857)
[kw]Theory and Microbiology, Pasteur Begins Developing Germ (1857)
[kw]Microbiology, Pasteur Begins Developing Germ Theory and (1857)
Germ theory
Medicine;germ theory
Pasteur, Louis
Diseases;and germ theory[Germ theory]
Biology;germ theory
[g]France;1857: Pasteur Begins Developing Germ Theory and Microbiology[3130]
[c]Health and medicine;1857: Pasteur Begins Developing Germ Theory and Microbiology[3130]
[c]Biology;1857: Pasteur Begins Developing Germ Theory and Microbiology[3130]
[c]Science and technology;1857: Pasteur Begins Developing Germ Theory and Microbiology[3130]
Bernard, Claude
Henle, Friedrich
Berthelot, Marcellin
Koch, Robert
Liebig, Justus von

Pasteur was well aware of the earlier work carried out by investigators on the process of fermentation. In his initial report on the subject in 1860, he acknowledged the contribution by French physicist Charles Cagniard de Latour Latour, Charles Cagniard de , who, in 1835, observed the decomposition of sugar and the production of carbon dioxide following the introduction of yeast. It was the belief of the time, though, that the yeast was consumed in the process. The prevailing theory was that fermentation was a purely chemical process.

Perhaps the leading proponent of this theory of fermentation was German chemist Justus von Liebig, Liebig, Justus von who argued that the fermentation process was a by-product of the decomposition of yeast and the subsequent release of enzymes. Indeed, it was well known that inorganic or nonliving material was capable of catalyzing certain fermentative reactions. Reflecting his background as a chemist, Pasteur’s studies on the subject primarily involved the quantitative measurement of reaction products, providing an explanation for how they were being consumed. For example, rather than being released as ammonia, nitrogen in the mixture was being converted into components within the yeast itself. Furthermore, Pasteur demonstrated that the sugar in the mixture is converted into cellulose (or at least a complex polysaccharide) within the yeast “globule.”

Perhaps the most important observation from the fermentation experiments was the effect on the quantity of the yeast itself. Pasteur carried out measurements on the yeast, demonstrating an increase in quantity as well as in the components that made up the microbe. Pasteur’s conclusion was that the yeast was a living organism, and that the process of fermentation was a biological process. Furthermore, the yeast was anaerobic, capable of growing and fermenting in the absence of oxygen. Pasteur also demonstrated that specific types of yeast were associated with different products of fermentations.

Pasteur continued this area of research with investigations into the souring of beer and wine. Observing several types of yeast in soured alcohol, Pasteur concluded that the problem originated with contamination from the environment. He found that mild heating would kill undesired contaminants, a process that would be known as pasteurization. In 1862, Pasteur and French physiologist Claude Bernard Bernard, Claude demonstrated that a similar heating process could also be used to preserve other beverages such as milk.

Pasteur’s biological theory of fermentation was repeatedly criticized. Marcellin Berthelot Berthelot, Marcellin , a French chemist Chemistry;of fermentation[Fermentation] , continued to argue in favor of a “modified chemical basis of fermentation.” Even Pasteur’s colleague, Bernard Bernard, Claude , had some doubts, but Pasteur’s experiments remained convincing, and gradually his ideas reached universal acceptance.

In 1865, Pasteur was asked by the French government to study a form of silkworm Silkworms blight known as pébrine. In the decade since the disease had been introduced into France, the silkworm industry was nearly ruined. Pasteur discovered the responsible agent was also a microorganism, a bacterium that infected the silkworm egg. He demonstrated that by isolating healthy eggs, and by providing bacterium-free leaves as a food source, the disease could be prevented.

Louis Pasteur.

Library of Congress

Pasteur’s earlier work on spontaneous generation proved that the atmosphere could be a source of microorganisms. The demonstration that pébrine was a bacterial disease gave credibility to the theory that diseases of humans and other animals might also be associated with similar organisms. Fermentation and putrefaction were clearly the products of microbial action, and Pasteur gradually developed the theory that fermentation and disease had a similar microbial basis. His primary focus until the mid-1870’s, however, was in the study of the fermentation of beer.

Before Pasteur, however, German anatomist and pathologist Friedrich Henle Henle, Friedrich suggested several decades earlier that there was a link between microbes and human disease. Henle’s later ideas for associating specific organisms with disease would become the basis for Robert Koch’s Koch, Robert postulates in the 1880’s. Pasteur’s introduction to the role of bacteria and animal disease involved the study of the anthrax bacillus.

Arguably, Pasteur’s most famous rival in this field was German physician Robert Koch. The competition was not always friendly, given the contemporary political background and history of relations between France and Germany. Nevertheless, Pasteur’s and Koch’s work was complementary, and it formed the basis for what became known as the germ theory of disease.

Pasteur confirmed the germ theory by showing that a specific bacillus is the cause of anthrax, and that when inactivated it could become the basis for an anthrax vaccine. Koch, meanwhile, developed a method to grow the organism, and others, in pure culture in the laboratory.

Around 1880, Pasteur had observed that the microbe that caused chicken cholera Cholera;and microbes[Microbes] could be inactivated by heating. When inactive microbes were inoculated into healthy chickens during an experiment, the animals developed immunity to the disease. In 1881, Pasteur applied this to his anthrax vaccine (and later in a vaccine against rabies Rabies ). Using a chemically inactivated strain of the anthrax bacillus, Pasteur demonstrated that a similar immunity could be developed in animals against this disease.


Although Louis Pasteur was not the originator of the germ theory of disease, his work proved the presence of microorganisms in the fermentation process and, by extension, in food spoilage. Applying this knowledge soon led to an understanding of how microbes are etiological agents of disease, initially in silkworms and then, later, in humans and other animals.

Pasteur’s early experiments demonstrated the lack of viability of the current theories of spontaneous generation. After establishing that contamination of beverages and most food resulted from organisms found in the environment, Pasteur developed the method that could be used to preserve these foods: pasteurization.

Pasteur’s work must be viewed in the context of the time, including the rivalry with Koch. Koch Koch, Robert was a physician, and his research was primarily in the area of medicine; Pasteur’s training was chemistry Chemistry;of fermentation[Fermentation] , and his work must be viewed from the context of chemistry. Pasteur had an ability to apply the knowledge from one area, fermentation as the result of microorganisms, to an analogous role played by such organisms in contaminating foods, and then applied this to infections in animals. Pasteur argued that by preventing such infections, disease could be prevented, a forerunner of aseptic techniques applied in surgery. Perhaps fortuitously, Pasteur also observed that if such “germs” were inactivated prior to inoculation of animals, the animal would develop an immunity to that disease: “Chance favors the prepared mind” representing one of Pasteur’s most important quotes.

Further Reading

  • Brock, Thomas, ed. Milestones in Microbiology, 1546-1940. Washington, D.C.: American Society for Microbiology, 1999. Reprints and commentary of many of the most important published works in the field of microbiology.
  • Bulloch, William. The History of Bacteriology. Oxford, England: Oxford University Press, 1938. Classic work on the subject, with the descriptive writing common for the time.
  • Debré, Patrice, Louis Pasteur. Translated by Elborg Forster. Baltimore: Johns Hopkins University Press, 1998. Comprehensive study of Pasteur’s life and work written by a French immunologist who describes his subject as “a living symbol, embodying both science and France.” Debré describes the scientific details of Pasteur’s experiments in simple, understandable language.
  • Dubos, René. Louis Pasteur: Free Lance of Science. New York: Plenum, 1960. The first major biography of Pasteur, as well as a history of his time.
  • Geison, Gerald. The Private Science of Louis Pasteur. Princeton, N.J.: Princeton University Press, 1995. Drawing upon manuscripts and papers not previously published, the author provides significant insight into Pasteur, his thought processes, and the experimental basis for his work.
  • Loudon, Irvine. The Tragedy of Childbed Fever. New York: Oxford University Press, 2000. Prior to Ignaz Philipp Semmelweis’s medical application of cleanliness in the 1840’s, 10 to 40 percent of women died from puerperal fever in the maternity hospitals of Europe. The author illustrates how the advent of germ theory, and the application of aseptic techniques, helped control the disease.
  • Waller, John. Einstein’s Luck: The Truth Behind Some of the Greatest Scientific Discoveries. New York: Oxford University Press, 2002. The author expands on the stories behind some of science’s greatest discoveries. Included is Pasteur’s experiments on spontaneous generation as well as Joseph Lister’s application of the germ theory to aseptic surgery.

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