Louis Pasteur

Key Facts & Summary

  • Thanks to his discoveries and his research activity, he is universally considered the founder of modern microbiology.
  • Pasteur demonstrated that in reality each microbe is derived from a pre-existing microbe and that spontaneous generation does not occur.
  • He developed techniques to attenuate the virulence of rabid spinal cord infected with rabies, proved that the material so obtained could be used to vaccinate dogs against the disease, and finally treated human beings who had been bitten by rabid dogs


Louis Pasteur, was a French chemist, founder of microbiology, known primarily for his work on pasteurisation of food and on preventive vaccines, was born in Dôle, province of Franche-Comté, on December 27, 1822. He received his scientific education at the École Normale Supérieure in Paris, obtaining his doctorate degree in Dijon (1847-1848) and Strasbourg (1848-1854), then professor of chemistry and dean of the Lille faculty of sciences, remaining until1867, when he was appointed professor of chemistry at the Sorbonne. Among the many honours accorded hum were membership in the Académie des Sciences (1862), the Académie de Médicine (1873), and the Académie Française (1882). He was the founder and director of the Pasteur Institute beginning in 1889.

Pasteur’s first discoveries, made while he was still a student, were in crystallography. He discovered molecular asymmetry by separating the two crystalline forms of tartaric acid and showing their opposite effects on polarised light. He further established that isomerism – the existence of two or more substances with the same molecular weight but with different physical or chemical properties – occurs in many other organic substances and that natural products occur in only one of the two isometric forms. They thus differ from molecules produced by chemical synthesis, which are mixtures in equal concentrations of both forms. He also recognised that living things exhibit selectivity with regard to their chemical action on isometric forms, a fact which prepared his mind for studies on fermentation. In Lille, he was consulted by an industrialist who had observed that undesirable products often appeared during the fermentation by which yeast transformed into alcohol.

The theory of fermentation in favour at that time was that yeast acted as a chemical catalyst on this transformation. Pasteur’s earlier studies on the production of optically active substances in the course of living processes led him to guess that yeast was not a chemical catalyst but a microscopic organism and that the conversion of sugar into alcohol was an expression of its biological activity. He postulated that the undesirable products in alcoholic fermentation came from microscopic organisms different from yeast which had taken the upper hand over the latter. Generalising this theory, Pasteur claimed that each particular type of fermentation was the effect of a specific microorganism – called the germs – acting on a specific type of substance to produce another substance. In rapid succession, he illustrated this revolutionary theory with brilliant studies on the conversion of sugar into lactic acid, butyric acid, or alcohol; of alcohol into acetic acid, etc. His germ theory of fermentation was first presented in 1857 in a short paper which has become a classic, Sur la fermentation appelée lactique (On Lactic Fermentation), in which he claimed that the different types of microbes could be separated from each other by proper techniques, and could be shown to differ in nutritional requirements, and susceptibility to antiseptics. He suggested, furthermore, that just as each type of fermentation was caused by a particular type of germ, so it was with many types of disease. Thus the fundamental tenets of the germ theory of fermentation and of disease were clearly stated in this preliminary paper.

Another great achievement in the biochemical field was Pasteur’s discovery that certain microorganisms derive energy from reactions which do not make use of oxygen. This discovery of anaerobiosis suggested to him that fermentation is the metabolic equivalent of respiration when life is carried out without oxygen.

Pasteur became preoccupied with the origin of microorganisms. It was then believed that the low forms of life could originate from organic materials during the souring of milk, the fermentation of grape juice, the putrefaction of met, etc. – a view that implied the spontaneous generation of microbes. By dramatic experiments, Pasteur demonstrated that in reality each microbe is derived from a pre-existing microbe and that spontaneous generation does not occur. Spoilage of perishable products could, therefore, be prevented by destroying the microbes already present and by protecting the sterilised material against subsequent contamination. Pasteur applied this theory to the preservation of beverages and foodstuffs, introducing thereby the technique of heat treatment, since called pasteurisation, which was first applied by him to the treatment of wine.

In 1865, Pasteur was asked to study the diseases of silkworms that threatened the silk industry in the south of France. He established a primitive laboratory in the mountains where the disease was prevalent. Three years of intensive work revealed two diseases in the silkworms, one caused by a parasitic protozoan, the other by faulty nutrition. Pasteur worked out techniques for the selection of noninflected worms and urged other steps for sanitary management of silkworm nurseries which led to rapid improvements in silk production.

The next phase of his scientific life was inaugurated around 1877 by studies of anthrax – a disease of farm animals which also affects man. Pasteur demonstrated that anthrax is caused by a particular bacillus which can survive in the carcasses of dead animals and in soil in the form of spores.

Pasteur’s phenomenal contribution to the germ theory of disease during the following ten years can best be presented under three separate categories which, however, he pursued simultaneously: 1) he undertook a crusade for measures to prevent or minimise the spread of disease by microbes, thus bringing about changes in hospital practices and inspiring Joseph Lister in England to develop antiseptic surgery. 2) Pasteur observed that birds which had been infected with old cultures of chicken cholera were resistant to infection with highly virulent cultures. From this, he concluded that attenuated forms of microbes could be used for immunisation. Shortly afterwards, he succeeded in attenuating the virulence of the anthrax bacillus and in a dramatic experiment vaccinated sheep and goats with an attenuated culture which protected animals against virulent anthrax. Thus was founded the science of immunisation. Pasteur perceived that his finding provided a theory for Edward Jenner’s practice of injecting cowpox material in order to provide protection against smallpox. To honour Jenner, he suggested that the attenuated cultures could be called vaccines (from Latin vacca, meaning cow) and their use, vaccination. 3) In 1882 Pasteur began to study rabies; he demonstrated that the disease was caused by a transmissible agent so small that it could not be seen under the microscope, thus revealing for the first time the world of viruses. He developed techniques to attenuate the virulence of rabid spinal cord infected with rabies, proved that the material so obtained could be used to vaccinate dogs against the disease, and finally treated human beings who had been bitten by rabid dogs. The work on rabies spread Pasteur’s fame all over the world, and public funds poured in for the creation of the Pasteur Institute in Paris.

Pasteur’s devotion to scientific research was complete; despite a stroke which partly paralysed him at the age of forty-six, he worked with incredible intensity until his health failed completely. He was highly intuitive, but also a masterful technician. He never shied away from practical problems, but also pursued large theoretical concepts and thus reached fundamental scientific generalisations. He worked in isolation with very few collaborators but had an immense gift for public debate. In many famous controversies, he overcame his opponents by dramatic and convincing demonstrations. While believing strongly in experimental science, he also maintained that there exist spiritual values that transcend the scientific approach, a thesis which he defended in a celebrated debate with the philosopher Joseph Ernest Renan.

Pasteur died in Villeneuve l’Etang, Seine-et-Oise, of September 28, 1895. All of his publications, as well as unpublished notes, have been assembled by his grandson Pasteur Vallery-Radot in a series of seven volumes entitled Oeuvres Complètes de Pasteur (The Complete Works of Pasteur).

Example of Pasteurisation

An example of pasteurisation is to be found in the dairy industry. Let’s take an example of milk: following the processes of clarification and homogenisation, the milk is pasteurised. Pasteurisation may be defined as the process of heating every particle of milk at 143° F. and holding for 30 minutes, or heating to 160° F. for 15 seconds. Pasteurisation at 143° F. is described as the vat or holding method, while the treatment at 160° F. is called high-temperature-short-time pasteurisation. Different equipment is used for each method.

Pasteurisation by the high-temperature-short-time method is a continuous process of heating, holding, and cooling. Heat economy is accomplished through a principle known as regeneration, in which the outgoing hot pasteurised milk heats the incoming unpasteurised milk. Final heating of the milk to pasteurisation temperature is accomplished with hot water. Final cooling of the pasteurised milk to 50° F. is accomplished with refrigerated water.

The principal reason for pasteurising milk is to provide public-health safeguard. The temperatures adopted are sufficient to destroy all pathogenic bacteria, including the tuberculosis organism, which is the most difficult to destroy by heat. Because milk is used so universally, pasteurisation is the only practical safeguard against epidemics. Pasteurisation also serves another useful purpose by prolonging the keeping qualities of the milk.


[1.] Berche, P. (2012). “Louis Pasteur, from crystals of life to vaccination”. Clinical Microbiology and Infection. 18 (s5): 1–6.

[2.] Bernard, D. (1980). The hundred years of Louis Pasteur. New Scientist. No. 1221. Reed Business Information. pp. 30–32.

[3.] Farley, J; Geison, GL (1974). “Science, politics and spontaneous generation in nineteenth-century France: the Pasteur-Pouchet debate”. Bulletin of the History of Medicine. 48 (2): 161–198.

[4.] Hoenig, Leonard J. (1986). “Triumph and controversy. Pasteur’s preventive treatment of rabies as reported in JAMA”. Archives of Neurology. 43 (4): 397–399.

[5.] Ligon, B. Lee (2002). “Biography: Louis Pasteur: A controversial figure in a debate on scientific ethics”. Seminars in Pediatric Infectious Diseases. 13 (2): 134–141.

[6.] Pasteur, Louis (1857). Mémoire sur la fermentation appelée lactique. Comptes Rendus Chimie (in French). 45: 913–916.

Image sources:

[1.] https://c1.staticflickr.com/8/7411/14006795038_3cf79a91b4_b.jpg

[2.] https://upload.wikimedia.org/wikipedia/commons/3/3c/Albert_Edelfelt_-_Louis_Pasteur_-_1885.jpg

[3.] https://upload.wikimedia.org/wikipedia/commons/1/16/Louis_Pasteur%2C_Ren%C3%A9_Vallery-Radot_and_their_families.jpg

[4.] https://upload.wikimedia.org/wikipedia/commons/9/93/PSM_V72_D022_Pasteur_institute_paris.png