The whole story

In 1847 Louis Pasteur, a young chemist freshly graduated from the prestigious Ecole normale supérieure, set to work on the problem posed by German physicist Eilhard Mitscherlich, namely, why do sodium ammonium paratartrate and tartrate – two seemingly identical chemical substances – affect polarized light differently?


Crystallography and molecular asymmetry


1847: research on molecular asymmetry

After several years of research involving crystallography, chemistry and optics, Louis Pasteur drew a parallel between the external form of crystal, its molecular make-up and its effect on polarized light. He discovered that asymmetric crystals deflect polarized light whereas this is not possible for crystals with a plane of symmetry.


He established a law of primary importance. "Only products originating under the influence of life are asymmetrical because they developed under the influence of cosmic forces which were themselves asymmetrical." Asymmetry is the major dividing line between the organic and mineral worlds.


Louis Pasteur’s work led to a new science: stereochemistry or spatial chemistry. It was also behind the emergence of synthetic chemistry.


Fermentation, a life's work from 1857 to 1862


1857: beginning of research on fermentation


It was while observing paratartrate crystals that Louis Pasteur discovered molecular asymmetry. When examining a paratartaric acid solution, he also noticed that the acid had fermented and been dissociated under the effect of mold. The fermented liquid now only contained left tartaric acid. The right tartaric acid had been decomposed or "disassembled". Thus a substance inactive on polarized light (paratartaric acid) had become active (left tartaric acid) under the effect of fermentation.

Before these findings it was universally acknowledged that fermentation was a death process according to the belief of the famous German chemist, Justus von Liebig. On completion of these experiments Louis Pasteur established a theory that ran counter to this dogma. Since all active substances come from the living environment, fermentation is a life process. Only life generates substances that are active on polarized light.


Through a logical sequence of studies, it was this initial observation that led from molecular asymmetry to fermentation and then on to contagious diseases.



1857-1862: beginning of research on fermentation


In 1854, at the age of 32 years Louis Pasteur was appointed Dean of the Science Faculty in Lille.

He was soon contacted by several of the region’s many distilleries. The distillers were concerned about variations in their beetroot alcohol production. They therefore requested Louis Pasteur to focus research on lactic acid and alcohol fermentation.


He noted that:

- alcohol fermentation is due to a living organism – ferment

- to study fermentation you need to:

- prepare a sterile fermentable culture medium, obtained through boiling

- inoculate the medium with a trace of pure ferment.

This was the basis of all microbiological techniques.


In studying the fermentation mechanism that confirmed the role and specificity of microorganism action, Louis Pasteur began to turn to biology. From this moment on he was no longer a mere chemist but also a biologist.


Louis Pasteur’s work raised a new set of research questions, such as "Where do fermentation agents come from?" and "Do they originate from germs similar to themselves or do they appear spontaneously as explained by the spontaneous generation theory?"


Spontaneous generation – the big debate


At the time the spontaneous generation theory was widely accepted in scientific circles. Louis Pasteur decided to approach the issue via his experimental method.

This required the use of swan-necked flasks. Water in the flask was brought to the boil for a few minutes until the steam escaped from the open end of the flask. It was then left to cool. While cooling, the air entering the flask deposited dust and germs on the first bend. Although in contact with outside air the liquid remained unaltered because germs could not get through.

Louis Pasteur showed that microbes were omnipresent – in water, in air, on objects, on the skin – and that some were responsible for diseases.


After some memorable struggles against his opponents, notably the famous biologist and fierce defender of the spontaneous generation theory, Félix Pouchet, in his 1862 paper Louis Pasteur was able to claim that:

- airborne dust contained microorganisms which develop and multiply.

- even the most putrescible liquids remained unadulterated if kept away from air (and hence these microorganisms) after heating.


He recommended ways of preventing and fighting these germs, and thus the habits essential for personal and social hygiene. This notably included the use of aseptic procedures, i.e. the various measures to be taken to prevent invasion of live tissue or inert environments by exogenous microorganisms or viruses. He advocated the importance of sterilization of linen and dressings, passing instruments through a flame and clean hands. These recommendations led to the widespread advent of modern surgery.


So how does fermentation work?


But Louis Pasteur still had ferments in mind. He pondered on fermentation and how ferments work. While studying butyric fermentation he discovered a new class of living organisms capable of living without air.


He used the term "anaerobic" to describe ferments able to live without air and "aerobic" for microorganisms requiring the presence of free oxygen to grow.

He came to the conclusion that fermentation is the consequence of life without air.

He applied his microbiological method to industry and agriculture to eradicate ancient diseases affecting crops and products.


To the rescue of industry and agriculture



He studied the formation of vinegar and the conversion of alcohol into acetic acid by Mycoderma aceti, which fixes oxygen from the air onto the alcohol. He showed vinegar makers how to produce vinegar of consistent quality by avoiding contamination by harmful mycoderma.


Wine diseases

Wine was France's flagship industry and a difficult business in many respects. Winemakers had difficulty guaranteeing the quality of their production which was affected by diseases of no known cause or cure. The crisis was nothing new but risked damaging exports and above all trade agreements in place with England. Emperor Napoleon III called on Louis Pasteur to seek a solution.

First he showed that each wine disease was due to a particular ferment.

He developed a protocol to fight the diseases, heating the wine to between 55°C and 60°C, a temperature at which it does not deteriorate and its bouquet is preserved. This method is now known worldwide as pasteurization.



Just like wine, beer is infected by microorganisms transmitted by airborne dust. Louis Pasteur taught brewers to preserve the wort from the impurities and to heat the beer to 55° to prevent disease.


Silkworm diseases


In 1865, disease hit the silk industry. In France, this posed a threat to the economy of an entire region and the disease spread further afield to other silk-producing countries such as Italy, Austria and Asia Minor.

Planche de Lackerbauer. Vers à soie. © Institut Pasteur

Louis Pasteur discovered that silkworms were affected by two diseases – silkworm nosema disease and flacherie.

Under the microscope, Louis Pasteur noticed that the worms with nosema disease developed shiny corpuscles, and showed that the disease was both hereditary and contagious.

He developed the cellular egg production method to enable the preservation of healthy silkworm eggs. He isolated the female moths to allow them to lay their eggs separately. After laying, he ground the female moths and examined them under the microscope. If the shiny corpuscles were observed he destroyed the eggs, otherwise he kept them for breeding.

As for flacherie, he introduced the "specific terrain" concept, i.e. the physiological condition of the infected host favoring outbreak of the disease. A few hygiene rules, good ventilation and quarantine of the suspect batches sufficed to prevent contamination.

These simple processes saved the silk industry from doom. But the research was of considerable value, paving the way for the study of contagious diseases. For the first time problems of heredity and contagion were scientifically proven and prophylaxis rules were established.

Between the age of 55 and 65 Louis Pasteur developed microbiology, applying it to medicine and surgery. Having established that diseases were caused by microorganisms, he then sought to identify and find a means of fighting them. His finest accomplishment was rabies.


Edward Jenner invented vaccination, Louis Pasteur invented vaccines

In 1877 he closely studied infectious diseases, discovering in turn:

  • staphylococcus as the cause of furuncles (boils) and osteomyelitis
  • streptococcus as the microbe responsible for puerperal infection
  • pneumococcus

Edward Jenner (1749-1823) had discovered that human beings could be protected against smallpox by inoculating them with the vaccine, a disease generally seen in cattle and identical to smallpox yet harmless in humans. Jenner’s discovery was based on exceptional circumstances – the existence of a disease similar to the human disease, but in animals, with a causative agent that triggers a protective response in humans.


Based on this principle, Louis Pasteur used the infectious agents themselves to achieve immunization. The processes were then applied to numerous diseases such as cholera (1878) and anthrax (1881).



He developed his method for attenuating microbial virulence for:

  • fowl cholera, through aging in contact with oxygen in the air, leading to development of a vaccine in 1878.
  • ovine (sheep) anthrax, through the culture of Bacillus anthracis at 43° attenuated by oxygen in the air. The vaccine was ready in 1881.
  • erysipelothrix infection

By applying his method to the study of infectious diseases (microbial agents), their prevention (asepsis), and their prophylaxis by immunization (vaccination), Louis Pasteur had founded the science of immunology.


Rabies and its invisible virus



Flacon de moelle épinière de lapin suspendue. © Institut PasteurIn 1880, Louis Pasteur’s experimental method was in full swing. He decided to apply it to the study of a human disease. He chose rabies because it affected not only humans, but also animals on which he could experiment.



Louis Pasteur's initial efforts to isolate the rabies virus proved unsuccessful as the virus remained invisible. Viruses could not be seen due to the poor resolution of the microscopes used. The virus was not seen until almost a century later, in 1962, with the advent of electron microscopy.


But as rabies is a disease of the nervous system, together with Emile Roux, Louis Pasteur then had the idea of inoculating part of a rabid dog’s brain directly into another dog's brain. The inoculated dog subsequently died.


The experiment was then conducted on rabbits as the risk for the experimentalists was less than with rabid dogs. After serial passage through several rabbits, the rabies incubation period was still six days. He had therefore produced a vaccine with stable virulence.


Louis Pasteur then attempted to develop a vaccine with attenuated virulence. He suspended sections of spinal cord from rabid rabbits inside flasks to dry in a moisture-free atmosphere. Virulence gradually declined until finally disappearing.


Louis Pasteur injected these spinal cord sections into rabid dogs, followed by preparations of increasing virulence. They did not develop rabies.


He then established a protocol to fight the disease effectively.

On February 25, 1884, together with Charles Chamberland and Emile Roux, Louis Pasteur announced the discovery to the French Academy of Science which appointed a study commission to assess the method’s efficacy. The method was deemed conclusive and approved.

However, despite the satisfactory results with dogs, Louis Pasteur feared testing it on humans.


Rabies overcome


On the morning on July 6, 1885, Louis Pasteur was given the opportunity to overcome his fears and test his treatment on humans when Joseph Meister was brought to him. The nine-year-old boy from Alsace had been bitten by a rabid dog fourteen times.


As Louis Pasteur was not a physician he requested Dr Grancher to inoculate the child. In the space of 10 days, Joseph Meister received a total 13 injections of rabid spinal cord that were progressively fresher (more virulent).

This first vaccination was a success. Joseph Meister never developed rabies and became the first ever human being to be vaccinated.


However, Louis Pasteur kept quiet about his success as the experiment had been conducted in relative secrecy.


It was a different story the second time round.

In September 1885, Jean-Baptiste Jupille, a 15-year-old shepherd, arrived at the Ulm street laboratory. He had been severely bitten by a rabid dog who had attacked six other shepherds. Jean-Baptiste Jupille had jumped on the dog to allow his friends to escape.

Louis Pasteur administered his treatment and was successful again. This time he vowed to tell the whole world his story.


Soon, vast numbers of people bitten by rabid animals came from all over France and abroad to the Ecole normale supérieure.


Given the numbers, Louis Pasteur set up a special rabies vaccination clinic which also doubled as a research and teaching center. Three years later the Institut Pasteur opened its doors.


Updated on 13/02/2014


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