Louis Pasteur

Louis Pasteur (December 27, 1822 – September 28, 1895) was a French microbiologist and chemist. He is known to the general public for his demonstration of the germ theory of disease and his development techniques of inoculation, most notably the first vaccine against rabies; however, he also made a major discovery in the field of chemistry, regarding asymmetric molecules and the polarization of light.

He also famously quoted: "Le hasard favorise l’esprit preparé" ("Chance favors the prepared mind").

Work on chirality and the polarization of light

In his early work as a chemist he resolved a problem concerning the nature of tartaric acid (1849). A solution of this compound derived from living things (specifically, wine lees) rotated the plane of polarization of light passing through it. The mystery was that tartaric acid derived by chemical synthesis had no such effect, even though its reactions were identical and its elemental composition was the same.

Pasteur noticed, upon examination of the tiny crystals of tartaric acid, that the crystals came in two asymmetric forms that were mirror images of one another. Tediously sorting the crystals by hand gave two forms of tartaric acid: solutions of one form rotated polarised light clockwise, while the other form rotated light counterclockwise. An equal mix of the two had no effect on polarized light. Pasteur correctly deduced that the tartaric acid molecule was asymmetric and could exist in two different forms that resemble one another as a left- and right-hand glove resemble one another. As the first demonstration of chiral molecules, it was quite an achievement, but Pasteur then went on to his more famous work in the field of biology/medicine.

His doctoral thesis on crystallography got him a position of professor of chemistry at the Faculté (College) of Strasbourg.

In 1854, he was named Dean of the new College of Science in Lille. In 1857, he was made administrator and director of scientific studies of the École Normale Supérieure.

Germ theory

Louis Pasteur demonstrated that the fermentation process is caused by the growth of microorganisms, and that the growth of microorganisms in nutrient broths is not due to spontaneous generation.

He exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass. Nothing grew in the broths; therefore, the living organisms that grew in such broths came from outside, as spores on dust, rather than being spontaneously generated within the broth. Thus, Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory.

While Louis Pasteur did not develop germ theory (Girolamo Fracastoro, Friedrich Henle and others had suggested it earlier), he conducted experiments that clearly indicated its correctness and managed to convince most of Europe that it was true.

Pasteur's research also showed that some microorganisms contaminated fermenting beverages. With this established, he invented a process in which liquids such as milk were heated to kill all bacteria and molds already present within them. He and Claude Bernard completed the first test on April 20, 1862. This process was soon afterwards known as pasteurization.

Beverage contamination led Pasteur to conclude that microorganisms infected animals and humans as well. He proposed preventing the entry of microorganisms into the human body, leading Joseph Lister to develop antiseptic methods in surgery.

In 1865, a disease called pebrine was killing great numbers of silkworms. Pasteur worked several years proving that it was a microbe attacking silkworm eggs which caused the disease, and that eliminating this microbe within silkworm nurseries would eradicate the disease.

Pasteur also discovered anaerobiosis - that some microorganisms can develop and live without air or oxygen.

Immunology

His later work on diseases included work on chicken cholera. During this work, a culture of the responsible bacteria had spoiled and failed to induce the disease in some chickens he was infecting with the disease. Upon reusing these healthy chickens, Pasteur discovered that he could not infect them, even with fresh bacteria: the weakened bacteria had caused the chickens to become immune to the disease, although they had not actually caused the disease.

This discovery was an accident. His assistant Charles Chamberland had been instructed to innocuate the chickens after Pasteur went on holiday. Chamberland failed to do this but instead went on holiday himself. On his return the month old cultures made the chickens unwell but instead of the infection being fatal as usual the chickens recovered completely. Chamberland assumed that an error had been made, and wanted to discard the apparently faulty culture out when Pasteur stopped him. Pasteur guessed that the recovered animals now might be immune to the disease as were the animals at Eure-et-Loir that had recovered from anthrax.

In the 1870s he applied this immunization method to anthrax, which affected cattle, and aroused interest in combating other diseases.

Pasteur publicaly claimed that he had made the anthrax vaccine by exposign the bacilus to oxygen. His laboratory notebooks now in the Bibliotheque Nationale in Paris in fact show that Pasteur used the method of a rival Jean-Joseph-Henri Toussaint, a Toulouse veterinary surgeon to create the anthrax vaccine. This method used the oxidizing agent potassium dichromate. Pasteur's oxygen method did eventually produce a vaccine but only after he had been awarded a patent on the production of an anthrax vaccine.

The notion of a weak form of a disease causing immunity to the virulent version was not new: this had been known for a long time for smallpox. Inoculation with smallpox was known to result in far less scarring and greatly reduced mortality than with the naturally acquired disease. Edward Jenner had also discovered vaccination, using cowpox to give cross-immunity to smallpox, and by Pasteur's time this had generally replaced the use of actual smallpox material in inoculation. The difference with chicken cholera and anthrax was that the weakened form of the disease organism had been generated artificially, and so a naturally weak form of the disease organism did not need to be found.

This discovery revolutionised work in infectious diseases, and Pasteur gave these artificially weakened diseases the generic name of vaccines, to honour Jenner's discovery. Pasteur produced the first vaccine for rabies by growing the virus in rabbits and then weakening it by drying the affected nerve tissue.

The rabies vaccine was initially created by Emile Roux, a French doctor and a collegue of Pasteur who had been working with a killed vaccine produced by desiccating the spinal cords of infected rabbits. The vaccine had only been tested in 11 dogs before its first human trial.

This vaccine was first used on 9-year old Joseph Meister on July 6, 1885 after the boy was badly mauled by a rabid dog. This was done at some personal risk for Pasteur, since he was not a licensed physician and could have faced prosecution for treating the boy. Fortunately, the treatment proved to be a spectacular success, with Meister avoiding the disease; thus, Pasteur was hailed as a hero and the legal matter was not pursued. The treatment's success laid the foundations for the manufacture of many other vaccines. The first of the Pasteur Institutes was also built on the basis of this achievement.

Honors and assessment

Pasteur won the Leeuwenhoek medal, microbiology's highest honour, in 1895.

He died in 1895 near Paris from complications caused by a series of strokes that had begun plaguing him as far back as 1868. He was buried in the Cathedral of Notre Dame, but his remains were soon placed in a crypt in the Institut Pasteur, Paris.

Pasteur's method of immunization was effective and was employed by many other physicians, eventually leading to the eradication of the diseases typhus and polio as threats. Pasteurization led to the elimination of contaminated milk and other drinks as sources of disease. In fact, Pasteur inaugurated the modern age of medicine, leading to an increase in the human life span and a surprising population explosion. Accordingly, he has been hailed as the "Father of Medicine" and a "Benefactor of Humanity." Craters on Mars and the Moon are named in his honor. In popular culture, Pasteur is the eponymous French scientist, his name appearing in science fiction shows like Star Trek. A biographical film of his life has also been made, entitled The Story of Louis Pasteur.

Miscellaneous facts

One of the few streets in Saigon,Vietnam that has not been renamed since colonial times is named in honour of Pasteur.