Pasteur's discoveries were among the greatest and most revolutionary. They transformed human life. Fields as varied as biology, industry, agriculture, medicine, surgery and hygiene have benefitted from the many applications of his research.
How it all began at the École Normale Supérieure
At the age of 24, Pasteur graduated from the École Normale Supérieure with an Advanced Degree in Physical Sciences and was nominated as the preparing technician.
1847: work on molecular dissymmetry
After several years of research combining crystallography, chemistry, and optics, Pasteur drew a parallel between the external shape of a crystal, its molecular make-up, and how it reacted to polarized light. Asymmetrical crystals deflected polarized light, while crystals with a plane of symmetry were unable to do so.
This work gave rise to a new science: stereochemistry, or chemistry in space.
Maladie des vins tournés. Ferment alcolique, filaments du parasite et cristaux de tartrate et de bitartrate de potasse. Aspect au microscope d'une goutte de vin tourné trouble. Maladie du vin. Provoqué par une bactérie lactique. Illustration, fig. 11 de "Etudes sur le vin" de Pasteur. (1866)Institut Pasteur
1857–1862: Pasteur's work on fermentation began
At the request of distillers in the north who were worried about inconsistencies in their production of sugar beet-based alcohol, Pasteur began to take an interest in lactic and alcoholic fermentations.
He found that alcoholic fermentation is due to a living microorganism, a round globule that multiplies, and that in defective fermentations, small rods appear that produce lactic acid.
Pasteur thus demonstrated that all fermentation is due to the presence of a microorganism, the ferment, and that each fermentation corresponds to a particular type of ferment.
1857-1862 : beginning of the work on fermentation
The study of butyric fermentation enabled Pasteur to understand how ferments work. These microorganisms live sheltered from the air and they borrow the oxygen they need to live from organic matter, thus decomposing it.
Pasteur made the distinction between the existence of aerobic species for which air is indispensable, and anaerobic species which develop without air.
In 1872, Pasteur was able to affirm that "fermentation is the consequence of life without air."
Spontaneous generation, the great debate
But where do the ferments come from? Are they born out of germs like themselves? Or do they appear spontaneously in fermentable materials?
At the time, the theory of spontaneous generation was deeply rooted in scientific circles. Pasteur approached this problem by conducting experiments. He did multiple experiments and demonstrated that all the dust in the atmosphere contained microorganisms that were always ready to develop and multiply. He proved that the most putrescible liquids remained unaltered if, after having been heated, they were kept without any air.
Flacons refermant de l'eau de levure, déposés ouverts à différentes altitudes par Pasteur pour observer les variations de multiplication des germes en fonction des lieux. De gauche à droite "Observatoire caves, Observatoire cour, Mer de glace 12 septembre 1860, Poupet 3 octobre 1860." Etudes de Pasteur sur la théorie de la génération spontanée.Institut Pasteur
The end of spontaneous generation
Pasteur completed his results with a new series of experiments, which proved that germs were not equally distributed in the atmosphere. He opened about 20 flasks of sterilized yeast water in different places:
- In the observatory courtyard, they all changed
- On the Jura plateau, eight deteriorated.
- At 2,788 feet (850 m) of altitude, five changed.
- On the Mer de Glace mountain, at an altitude of 6,562 feet (2,000 m), only one changed.
After these memorable battles to prove his staunch critics wrong, Pasteur was able to conclude that 'spontaneous generation is an illusion, and that living beings, notably ferments, are not born spontaneously.
Flacons refermant de l'eau de levure, déposés ouverts à différentes altitudes par Pasteur pour observer les variations de multiplication des germes en fonction des lieux. De gauche à droite "Observatoire caves, Observatoire cour, Mer de glace 12 septembre 1860, Poupet 3 octobre 1860." Etudes de Pasteur sur la théorie de la génération spontanée.Institut Pasteur
All of this work led him to think about how we could protect ourselves from microbes, particularly during surgery. He went on to advise that cloths and dressings should be sterilized at a temperature of 266°F (130°C), instruments should be heated up, and hands should be clean. These basic hygiene methods are still used in all hospitals today.
Pasteurization
Three major industries—vinegar, wine, and beer—benefited greatly from his advice.
Louis Pasteur highlighted the role played by mycoderma aceti in vinegar production and showed vinegar makers how to obtain vinegar of consistent quality. He demonstrated that each disorder occurring in wine was caused by a particular ferment. To stop these disorders from developing, he heated the wines for a few minutes at 131°F (55°C).
Louis Pasteur taught brewers to keep the must free from dirt and to heat the beer to 131°F (55°C). This method, which can be applied to all spoilable liquids, is known throughout the world as pasteurization.
The silk industry in danger
In 1865, silk production was devastated by a disease that ravaged silkworms. In France, the entire economy of a region was at stake, and the epidemic spread to other silk-producing countries such as Italy, Austria, and Asia Minor.
Louis Pasteur realized that silkworms were being affected by two diseases: pebrine and flacherie. Under a microscope, Pasteur saw that worms affected by pebrine developed shiny corpuscles. This also showed that pebrine is a hereditary and contagious disease.
The method of cell graining
To preserve the breeding of healthy silkworms, he developed the cellular egg production method, isolating the female butterflies to allow them to lay eggs separately. Once the eggs had been laid, he crushed the female butterfly and examined it under a microscope. If he observed the presence of shiny corpuscles, he destroyed the eggs. Conversely, if there were no shiny corpuscles, he kept them for further breeding.
The prelude to the study of contagious diseases
As for flacherie, he highlighted the notion that a "particular terrain," i.e., the physiological state of an infected host, is what makes the disease occur. Simple hygiene precautions and good ventilation, as well as the quarantining of suspected batches, were sufficient measures to prevent contamination. These very simple procedures saved silk production and were of considerable interest. For the first time, the problems of heredity and contagion were scientifically elucidated, and the rules of prophylaxis (a set of medical measures that are implemented to prevent the appearance, aggravation or spread of diseases) were established.
The role of microorganisms in disease development
From 1877 onwards, he embarked on the study of anthrax, which was wiping out sheep and cattle. He confirmed that, as the German Robert Koch had just announced, the disease was caused by a specific microbe called Bacillus Anthracis. This was the first proof that microbes can cause diseases. Koch had shown that this bacterium could give rise to very resistant dehydrated forms, called spores. Pasteur demonstrated that the epidemic spread rapidly in herds because farmers were in the habit of burying anthrax-ridden animals in their fields, which meant that the bacterial spore could be brought back up to the surface by earthworms. As a result, the sheep caught it while they were grazing.
Numerous pathogens identified
In the following years, Pasteur and his collaborators identified a number of pathogenic microbes: staphylococcus (in clusters of cocci), the cause of boils and osteomyelitis; streptococcus (in chains of cocci), responsible for puerperal infection, and pneumococcus, the agent responsible for pneumonia.
Statue élevée à la mémoire de Jenner (1749-1823) sur la place des bains à Boulogne le 11 septembre 1865. Gravure (d'aprés photo) extraite d'un livre.Institut Pasteur
Immunization against infectious diseases
But Pasteur remained obsessed with one idea: protecting against infectious diseases.
Edward Jenner (1749–1823) had discovered that humans could be protected against smallpox by inoculating them with vaccinia, a disease usually found in cattle that is very similar to smallpox but harmless to humans.
Immunization against infectious diseases
Jenner's discovery was based on an exceptional circumstance, namely the existence in animals of a disease similar to the human version, the agent of which could be used to protect humans. Based on this principle, Pasteur used the infectious agents themselves. He attenuated their virulence to obtain the immunization and expanded this process to develop vaccines against hen cholera (1879–1880) and sheep anthrax (1881).
The fundamentals of immunology
By applying his method to the study of infectious diseases (microbial agents) and their prophylaxis by immunization (vaccination), Pasteur became the founder of immunology.
