Louis Pasteur remains one of the largest scientists of the XIX E century: so for the general public he is the father of vaccination, the biologists hold it for that which put an end to the antiquated concept of spontaneous generation; with the eyes of the doctors, it has the appearance of a pioneer as regards hygiene; for the industrialists of agroalimentary, he is the inventor of a method of destruction of the pathogenic bacteria to which its name is attached.

In 1848, Pasteur supports a doctorate on molecular dissymmetry. Crystallography was then a discipline still incipient: the bases had been thrown by it by the French abbot Rene Just Haüy in 1784, and the rotatory polarization of the light (discovery by the French François Arago and Jean-Baptiste Biot in 1811) was studied only recently.

Its passion for tartrates

In 1844, the German Eilhard Mitscherlich, by studying the properties of the paratartrate and ammonia tartrate, two salts formed by the tartaric acid during the fermentation of the wine, had discovered that their optical activities, i.e. their capacity to deviate the direction of a beam of light (polarization), were different. Although they were of the same chemical composition and of the same crystalline form, with the same specific angles, only the tartrate deviated the beam of light.  

Pasteur will show that it is the slope of the crystalline facets which is at the origin of the phenomenon and which the two compounds are structurally the image one of the other in a mirror, i.e. they are two optical isomers, or enantiomers. Pasteur places himself already at the border which separates chemistry from the alive nature of that of the still life, because molecular dissymmetry is an exclusive property of the organic substances. In 1848, it is named supply teacher of chemistry at Strasbourg, city where it marries one year later Marie Laurent, girl of the vice-chancellor of the university, and continues his research on the tartaric acid. J. - B. Biot, after having checked the results of Pasteur, will present them to the Academy of Science in 1853.  

Fermentation with the micro-organisms

In 1854, Pasteur becomes full professor and senior of the very new Faculty of Science of Lille. It is interested under investigation of fermentations, at the request of an industrial inhabitant of Lille who wondered why the beet juice deteriorated out of alcohol. The German chemist Justus von Liebig thought at the time fermentations were only chemical reactions occurring exclusively in the alcohol put in the presence of oxygen (acetic fermentation).  

Preceding work of Pasteur on molecular dissymmetry leads it to conceive fermentation like a vital act and not like a simple chemical reaction: the pentanol (which results from the fermentation of sugar) is an organic molecule, which has a molecular dissymmetry. In the chemical theory of fermentation, the yeasts intervened only because they contain albuminoid substances. Pasteur shows the role except for whole yeasts in the fermentation of alcohol sugar, and allots a character living of micro-organisms to them.

Refutation of the spontaneous generation

In 1857, Pasteur comes to settle with Paris, indispensable condition of entry to the Academy of Science. He is named sub-manager of the scientific studies of the Teacher training school. As of its arrival in the capital, he studies the vinegar and the conservation of the wines. He will show into 1859 that fermentation also exists in milk and that it is held there even in the absence of the ion ammonium NH4 +, which brings albumin that one thought essential. He notes that the presence of oxygen is not necessary, certain fermentations (alcoholic, lactic or butyric) occurring safe from the air (anaérobiose). The same year, its work leads it to find the means of excluding the idea from spontaneous generation, which persisted since Antiquity.  

In 1860, Pasteur shows that a fermentable liquid boiled in contact with a calcined air can ferment only if one places on the collar of the bottle a dusty cotton flock. He is opposed thus to the French doctor Felix Archimedes Pouchet, whose publication of 1858 affirmed power to be the proof of the spontaneous generation of yeasts. The debates, very animated, were largely popularized through the media, because the question shook the philosophical bases of a whole generation, so much so that the Academy of Science put it in 1860 at the program of the entrance examination. Pasteur, only candidate, there is received in 1862 for his work on the organized Corpuscles which exist in the atmosphere, in which it shows the presence of a germ at the beginning of any alive production and refutes the possibility of a spontaneous generation.  

Conservation of the wine and food

In 1863, at the request of Napoleon III, he seeks to develop a process of conservation of the wines. The filtration, which consists in removing the wine from its impurities by making it pass through a porous element, but also the sulfur addition, which, by its disinfectant effect, acts on the leavens, ensures from now on the wine its stability and its healthy evolution. Preceding work of Pasteur in addition gave rise to another process of conservation of the food (milk, fruit juice, etc): it is the pasteurization, which consists in heating food at a sufficient temperature to destroy all the pathogenic bacteria which are there.  

In parallel, Pasteur is named chemistry teacher at the National school of the fine arts. In 1867, its administrative mission at the Teacher training school ends: its rigor and its severity led it to be ousted about it, at the request of the minister Victor Duruy, under pretext of a reorganization of the studies. In fact, Pasteur had refused to intervene in favor of a pupil returned to have forwarded a letter of congratulations to Holy-Beuve, which had just made with the Senate a speech on freedom. At once appointed professor in the Sorbonne, it gives up this station very quickly, because it wants from now on to be devoted entirely to its work. It is embanked by an hemiplegia in 1868 and, until its death, will preserve after-effects on the left side of them. It completes its work on fermentations by finally showing the role and the specificity of the leavens, in particular of brewers' yeast, with its pupil Emile Duclaux, in 1870. Pasteur, by his work on fermentations, will oppose Liebig, but also in Claude Bernard, who, the year even of her death (1877), was always persuaded of the spontaneous generation of alcoholic yeast and still doubted the role of yeast in fermentation. Napoleon III names Pasteur senator with life for service rendered to the nation, but the war of 1870 will prevent that the imperial decree is validated.  

Disease with the microbe

All its studies little by little led Pasteur to medicine, because there is not far from the fermentation with the putrefaction and of the putrefaction to the morbid puses and other phenomena. Already in 1865, J. - B. Dumas, senator of Gard, had called it in Alès, where the colonies of worms with silk were decimated by a disease, the pébrine; their exploitation was threatened, so much so that the merchants turned to Japan. Studying the disease (without however being able to cure it), Pasteur notes that it is due to the multiplication of a bacterium in the intestine of the animal: it is consolidated in the idea that the infectious illness is due to micro-organisms. In 1863, Pasteur between with the Academy of medicine.  

Casimir Joseph Davaine had, about ten years before, located the origin of a disease (the coal of the sheep) in the presence of a bacterium. This idea being reinforced by its own experience, Pasteur enjoins the French surgeons to take measures of asepsis before operating the wounds and measurements of antisepsy to look after them. It succeeds in this field still incipient with the Hungarian obstetrician Ignaz Philip Semmelweis, who asked his fellow-members to wash the hands with chloride of lime before exerting (1846), and with the English surgeon Joseph Lister, who advised with his to treat the wounds with phenol (1867).  

In 1878, Pasteur and his collaborators make a communication with the Academy of Science, the Theory of the germs and his applications to medicine and the surgery, in which microscopic living beings - named then “microbes”, one month after Charles-Emmanuel Sédillot, surgeon, had proposed this term - are declared responsible for diseases.  

The idea that certain micro-organisms can be the cause of diseases becomes obsessional until in the manner of living of Pasteur: a preparer of its laboratory reports that it had the particularly miserly handshake and that, when suitabilities led it to be subjected to it, it washed the hands then meticulously. Others tell that it made carry to all its close relations a handkerchief in front of the mouth when they passed in front of the Laennec hospital. Pasteur will discover in 1878 the streptococcus responsible for the angina, then in 1880 that of the staphilococcus, person in charge of the boils.

To vaccinate to prevent

Pasteur also studies closely works of Edward Jenner, pioneer of the fight against the infectious illness: antivariolar vaccination is effective since the end of the XVIII E century, and Pasteur has the intuition that nonvirulent stocks of microbes could have the same protective effect against the diseases that they cause that the virus of vaccinates against variola. Its work concerns on the cholera of hens and the disease of coal. In 1879, his/her Red-headed Emile collaborators and Charles Chamberland inadvertently leave in the drying oven all the cultures of the microbe of the cholera: this handling error is salutary to Pasteur, who discovers a method then - ageing with the air - to attenuate the virulence of the microbes.