Louis Pasteur

Born 1822
Died 1895

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French chemist and bacteriologist, born December 27, 1822, Dôle, Jura, eastern France; died September 28, 1895, Chateau Villeneuve-l'Étand, near Paris.

Biography of Louis Pasteur

Chance favours only the prepared mind.

Louis Pasteur was a founder of the science of bacteriology, proving that that microorganisms cause fermentation and disease. He was the first to use vaccines for rabies, anthrax, and chicken cholera. His work was vital to saving the beer, wine, and silk industry of France and other countries. In his early years he did pioneering work in stereochemistry, and he originated the process known as pasteurization.

His contributions seem to follow a saying he made in his inaugural address as dean of the new faculty of science in Lille: "When it comes to observations, chance only favours the prepared mind"

Youth
Pasteur was the grandson of Jean-Henri Pasteur (1769-1796) who had moved to Besançon where he worked as a tanner. His only son, Jean-Joseph Pasteur (1791-1865), was Louis Pasteur's father. He was drafted into the French Army in 1811 and served with the celebrated Third Regiment of Napoleon's army. When he was discharged in 1814 he had attained the rank of sergeant major and had been awarded the cross of the Legion of Honour. Upon his return to civilian life, Jean-Joseph Pasteur also became a tanner, initially at Besançon. In 1816 he married Jeanne-Étienne Roqui, daughetr of a gardener from a family of the Franche-Comté. They moved to Dôle. In 1826 the family moved to Arbois, a town of about 8,000 inhabitants. It was here Louis Pasteur, born in Dole in 1822, grew up.

After attending the École Primaire from 1831 he entered the Collège d'Arbois in 1837. At his early age he showed little interest in anything but drawing and produced a number of pastels, portraits of his parents and friends, and he was an enthusiastic angler. In 1838 he spent one month in Paris, but less than a month later, overwhelmed by homesickness, he returned to Arbois

The Senior Pasteur did not see his son ending up as an Artist. His highest wish for his son was that he complete his education in the local schools and become a professor in the college at Arbois. Louis now continued his education at the Collège Royal de Besançon, showed increasing interest in chemistry and other scientific subjects, and performed superbly at the Collège. He received his bachelor's degree in letters on August 29, 1840.

However the headmaster of the college recognized that Louis could do much better and convinced father and son that Louis should try for the École Normale Superieure in Paris. This most prestigious French University was founded specifically to train outstanding students for University careers in science and letters.

Two years later, on August 13, 1842, Louis received his bachelor's degree of science (bachelier ès sciences) and was declared admissible to the École Normale. He then attended Barbet's boarding school, before entering the École Normale in the autumn of 1843. In 1845 he became licencié ès sciences (Master of Science). For a period he was the laboratory assistant to Antoine J. Ballard

Crystal clear
Louis Pasteur, the father of microbiology and immunology, launched his scientific career by studying optical activity and the shapes of organic crystals. On May 22, 1848, at the age of 26, he presented before the Paris Academy of Sciences a paper announcing the discovery of small hemihedral facets on the crystals of nineteen compounds he had studied. In all of them the hemihedral facets inclined in the same direction and the direction of the optical activity was the same.

He had discovered that certain chemical compounds were capable of splitting into a "right" component and a "left" component, one component being the mirror image of the other. He tediously sorted the crystals by hand, using a Nicol prism, observing two forms of tartaric acid: solutions of one form rotated polarised light clockwise, while the other form rotated light counter clockwise. 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 left- and right-hand gloves resemble one another. The Nicol prism is a device to produce polarised light. It was invented in 1828 by the scottish physicist William Nicol.

Tartaric acid forms in grape fermentation that is widely used commercially, and in racemic acid – an acid that had then been discovered in certain industrial processes in the Alsace region.

This was the foundation of stereoscopic chemistry and earned him the Rumsford Medal from the Royal Society of London in 1856.

Professor
In 1848 Pasteur was appointed professor of physics at the Dijon Lycée (secondary school) but on December 29 that year he was called to the University of Strasbourg as professeur suppléant in chemistry. There, on May 29, 1849, he married the daughter of the rector of the university, Marie Laurent, by whom he was to have five children, only two of whom survived childhood. A son, Jean Baptiste, born 1851, became a diplomat, and a daughter, Marie-Louise, in 1879 married René Vallery-Radot, later Pasteur's biographer.

At Strasbourg, Pasteur continued and greatly expanded his work on optical activity and molecular asymmetry despite expanding teaching duties.

In 1854 he was named professor of chemistry and dean of the new science faculty at the University of Lille, where he initiated a highly modern educational concept: by instituting evening classes for the many young workmen of the industrial city, conducting his regular students around large factories in the area, and organizing supervised practical courses, he demonstrated the relationship that he believed should exist between theory and practice, between university and industry. On these tours to the factories, Pasteur was quick to advise the managers that he was available to help solve their problems.

In the summer of 1856, a mr. Bigot, father of one of his students in chemistry, called upon Pasteur to help him overcome difficulties he was having manufacturing alcohol by fermentation of beetroot. Often, instead of alcohol, Bigot's fermentations yielded lactic acid. Pasteur entered M. Bigot's factory, microscope in hand, and thus began his studies on fermentation.

Milk or booze?
Pasteur quickly found three clues that allowed him to solve the puzzle of alcoholic fermentation. First, when alcohol was produced normally, the yeast cells were plump and budding. But when lactic acid would form instead of alcohol, small rod-like microbes were always mixed with the yeast cells. Second, analysis of the batches of alcohol showed that amyl alcohol and other complex organic compounds were being formed during the fermentation. This could not be explained by the simple catalytic breakdown of sugar shown by Antoine Lavoisier (1743-1794). Some additional processes must be involved. He concluded and was able to prove that living cells, the yeast, were responsible for forming alcohol from sugar, and that contaminating microorganisms turned the fermentations sour. That yeast is an organism capable of reproducing itself, even in artificial media, without free oxygen, is a concept that became known as the Pasteur effect.

Over the next several years Pasteur identified and isolated the specific microorganisms responsible for normal and abnormal fermentations in production of wine, beer, and vinegar. He showed that if he heated wine, beer, milk to moderately high temperatures for a few minutes, he could kill living micro organism and thereby sterilize (pasteurize), the batches and prevent their degradation. If pure cultures of microbes and yeasts were added to sterile mashes uniform, predictable fermentations would follow.

A farewell to spontaneity
In August 1857 he presented a short memoir on lactic fermentation to the Société des sciences, d'agriculture et des arts de Lille. Pasteur's results aroused tremendous controversy because it contradicted the popular theory of spontaneous generation – that life could arise spontaneously in organic materials. Pasteur vigorously opposed this theory and he proved it to be wrong by showing that if he placed liquid in a flask and boiled it, but left the flask open, putrefaction would occur, whereas if the neck of the flask was drawn to a fine point – a swan neck bottle – or sealed off, the solution would remain pure. This experiment was similar to one conducted by the Italian physician and philosopher/poet Francesco Redi (1626-1697), and with the same results (see article about Lazzaro Spallanzani, 1729-1799).

In October 1857 Pasteur was named administrator and Director of Scientific Studies at the École Normale Supérieure. His duties included "the surveillance of the economic and hygienic management, the care of general discipline, intercourse with the families of the pupils and the literary or scientific establishments frequented by them." These positions included neither laboratory nor allowance for research expenses, but by 1862 he had secured his own research laboratory in a small pavilion.

In November 1860 Pasteur described the successful cultivation of Penicillum "or any mucedinous fungus" in a medium of pure water, cane sugar, phosphates, and an acid ammonium salt.

No administrator
Pasteur was elected to the Academy of Sciences in 1862, and the following year a chair at the École des Beaux-Arts was established for him for a new and original program of instruction in geology, physics, and chemistry applied to the fine arts. Here he introduced laboratory procedures oriented toward the problems of art and its materials.

As a scholar engaged in research, Pasteur eventually found his administrative duties as Director of Scientific Studies at the École Supérieure too irksome. He gave up the post in 1867, and, thanks to the support of Emperor Napoleon III to the minister of public instruction, a laboratory of physiological chemistry was created for him at the same institution. The cost of 60,000 francs was shared equally by the Ministry of Public Instruction and the Ministry of the House of the Emperor. The new laboratory, thirty meters long, was to be linked by a gallery with the pavilion Pasteur had occupied since 1859.

The grapes of wrath
In 1864 the wine industry in Jura was being injured by a disease which caused the wine to be sour. Pasteur showed that this was because of organisms which are bottled with the wine. On May 1, 1865, he told the Académie des Sciences that his attempts to cure diseased wines with chemical antiseptics had been less than satisfying, but that that the problem could be eliminated by heating the wine for a short period of time to 60 °C. This process has later been used in many areas, particularly in milk, and is called "pasteurization".

A silken problem
Between 1855 and 1865 the silkworm industry in France was crippled by a disease called pébrine. This was so called because the worms developed black pepper like spots. The problem had started in 1849, and by 1865 the total revenue loss was estimated at 120 million francs in Alais alone. Alais, now Alès, was the centre of French sericulture.

Pasteur was asked by the French government to attempt to overcome this menace. The work began in 1865, but was interrupted when Pasteur dropped his work because of the deaths of his father and two of his daughters, and before going back, spent a week at the Palace of Compiegne as the guest of Napoleon III.

Pasteur and his group worked for five years near Alais when microscopic examination convinced him that the disease was caused by bacteria and that the worms had to be bred from eggs which were healthy. Just as he had discovered this he found that there was another disease affecting the silkworm, flacherie. This initially caused him to be quite depressed after the years of work that he had put into the project. However, finally he realized that the disorder was due to the mulberry leaves being infected by bacteria causing a very infective intestinal disease. He showed that this could be prevented by using healthy mulberry leaves.

These findings saved the French silk industry, but prior to the successful termination of his studies, he had been subjected to a great deal of criticism, for his lack of success. Furthermore, the seed merchants themselves spread rumours about his lack of success because they feared the financial loss that might be incurred.

I 1868 Pasteur suffered a cerebral haemorrhage that caused a temporary partial paralysis and loss of the ability to speak. He applied for retirement from the university, but after a few months he had recovered completely and continued his work.

In 1873 he was elected a member of the Academy of Medicine, and in 1874 the French Parliament provided him with an award that would ensure his material security while he pursued his work.

War, beer, and anthrax
In 1870 the Franco-Prussian war broke out, and Pasteur, who was an intense nationalist, returned his honorary diploma of Doctor of Medicine sent him two years earlier from the University of Bonn. Perhaps as a result he set out to improve French beer, which resulted in him showing that one of the problems with the industry was again micro-organisms which were different from the beer yeast. Again he showed that pasteurization could produce a much superior product.

Almost from the beginning of his work on fermentation and spontaneous generation, Pasteur made frequent references to its potential medical implication. Sharing the common belief that fermentation and disease were analogous processes, he naturally supposed that the germ theory could apply to disease as well as to fermentation – as Theodor Ambrose Hubert Schwann (1820-1882), among others, had supposed before him.

During the 1850's and 1860's important work was done on anthrax by French scientists, and in particular by the German bacteriologist Robert Koch, who discovered the Bacillus anthracis in 1876. Pasteur had long planned to do research on anthrax, and from about 1877 he studied anthrax and chicken cholera.

Pasteur noticed that chickens were immune to anthrax, and postulated that it was because chickens have high body temperatures of 43-44 °C. To test this hypothesis, he lowered the body temperature of a chicken to 37° C and found it to be susceptible to anthrax.

He succeeded in isolating the organism involved in chicken cholera and discovered that old cultures of this organism lost their virulence but could be used on injection to protect the animals from inoculation with a virulent culture. He applied similar approach to anthrax and developed an attenuated culture which could be used to protect animals from infection. In this he was following the example of the English physician Edward Jenner (1749-1823) in his method for vaccinating animals against cowpox.

Then, in 1881, Pasteur did his famous experiment at Pouilly-le-Fort with vaccinated and unvaccinated animals – sheep and cows. Pasteur heated anthrax germs and inoculated 25 sheep. The efficiency of the vaccine was proved when all vaccinated sheep survived, while all sheep inoculated with anthrax died.

At this time, anthrax posed a severe threat to French agriculture and animal husbandry. According to Pasteur, estimates of the annual loss from anthrax ranged from 20 to 30 million francs.

This work was continued by Pasteur's work to find a vaccine against swine erysipelas, which in 1882 had claimed an estimated 20,000 animals in the departments of the Rhône Valley alone and in 1879 an estimated 900,000 hogs in the United States. The work was done with, among others, Louis Thuillier (born 1856), who died of cholera in September 1883, two months before Pasteur gave the Académie des Sciences an account of their studies. The research resulted in a vaccine that was used on more than 100,000 hogs in France between 1886 and 1892, and on more than 1 million hogs in Hungary from 1889 to 1894.

Rabies
On April 27, 1882, Pasteur was elected a member of the Académie Française. At that time he had worked for two years on the research that proved to be the most spectacular of all – the preventive treatment of rabies. Because rabies is so rare in man (in France its victims probably never reached more than 100 in any year) and can be quite readily controlled by muzzling and quarantine of dogs, many observers of Pasteur's career have been somewhat puzzled by his interest in it. Some have traced his concern to a traumatic childhood experience. In October 1831 a rabid wolf bit several Arboisiens and terrorised the entire region. The standard treatment, then as in antiquity, was to cauterize the wounds immediately with a red-hot iron, and the young Pasteur reportedly saw a man submit to this excruciating procedure at a blacksmith's shop near his home. Despite all efforts some of the wolf's victims died, including at least one whose name and circumstances Pasteur recalled more than half a century later.

In May 1881, in his first memoir on rabies per se, Pasteur described a new experimental method for transmitting the disease with certainty and with a greatly reduced incubation period. The new method involved the extraction of cerebral matter from a rabid dog under sterile procedures and its subsequent inoculation directly onto the surface of the brain of a healthy animal. Under these conditions the inoculated animal invariably contracted rabies after an incubation period of about two weeks.

After experimenting with inoculations of saliva from infected animals, he came to the conclusion that the virus was also present in the nerve centres, and he demonstrated that a portion of the medulla oblongata of a rabid dog, when injected into the body of a healthy animal, produced symptoms of rabies. By further work on the dried tissues of infected animals and the effect of time and temperature on these tissues, he was able to obtain a weakened form of the virus that could be used for inoculation.

In the summer of 1885 Pasteur was closing in. By that time he reported that he had rendered fifty dogs of all ages and types refractory to rabies. Then came the great challenge.

The first survivor of rabies
Joseph Meister, a nine-year old boy from Alsace, was brought to Pasteur's laboratory by his mother, who could tell that her son had been bitten by a rabid dog two days earlier. With them was also the owner of the dog. Two days before, on July 4, Meister had been bitten in fourteen places on his hands, lower legs, and thighs. These wounds, some so deep that he could scarcely walk, had been cauterized with carbolic acid by a local physician twelve hours after the attack. The dog had been killed by its owner, whom Pasteur sent home after having been assured that his skin had not been broken by the dog's fangs. That the dog was indeed rabid seemed certain from its behaviour and from the presence in its stomach of hay, straw, and wood chips.

Pasteur immediately consulted Edmé Félix Alfred Vulpian (1826-1887), a member of the rabies commission, and Jacques-Joseph Grancher (1843-1907), who worked in his laboratory. Both considered young Meister doomed; and after Pasteur told them of his new results, both urged him to use the new method on the boy. The treatment, begun that evening, July 6, 1885, lasted ten days, during which Meister received thirteen abdominal injections derived from progressively more virulent rabbit marrows. By the end of the treatment, Meister was inoculated with the most virulent rabies virus known, that of a mad dog augmented by a long series of passages through rabbits. Nonetheless he had remained healthy during the nearly four months since he had been bitten, and his recovery therefore seemed assured. It is said that Pasteur suffered great mental qualms, and hardly was able to sleep or work during the period he treated the boy.

Shortly after Pasteur treated a second boy, a fifteen-year old shepherd name Jean-Baptiste Jupille, who had been viciously bitten while killing a rabid dog that threatened the lives of six younger comrades. He had not arrived at Pasteur's laboratory for treatment until six days after having been bitten (as compared to two days for Meister), but the treatment was equally successful.

"After making almost innumerable experiments, I have discovered a prophylactic method which is practical and prompt, and which has already in dogs afforded me results sufficiently numerous, certain, and successful, to warrant my having confidence in its general applicability to all animals, and even to man himself."

Joseph Meister eventually became a concierge at the Institut Pasteur and lived until 1940, when he chose to commit suicide rather than open Pasteur's burial crypt to the advancing German army.

The Pasteur Institute
The successful experiment got an enormous publicity. Already the following year close to 2,500 persons had been vaccinated in Paris alone. Pasteur's laboratory, however, was too small to handle such an inflow, and a foundation was set up to fund a new institute. This foundation received contributions from the tsar of Russia, the emperor of Brazil, and the sultan of Egypt, as well as from the French people. The Académie des Sciences then took the imitative to establish the Pasteur Institute. The institute was inaugurated in Paris for the purpose of undertaking fundamental research, prevention, and treatment of rabies. Pasteur's ailing health prevented him from working actively in the new institute, but formally he headed the institute until his death

Of the 350 first patients treated with Pasteur's method, only one had died, the ten-year old Louise Pelletier, who had arrived for treatment thirty-seven days after being attacked. By 1905, 100,000 persons had undergone Pasteur's treatment at centres throughout the world, and by 1935 51,057 persons had been treated at the Institut Pasteur alone, with only 151 deaths.

The revolutionary scientist
Louis Pasteur brought about a veritable revolution in the 19th-century scientific method. By abandoning his laboratory and by tackling the agents of disease in their natural environments, he was able through his investigations to supply the complete solution to a given question, not only identifying the agent responsible for a disease but also indicating the remedy.

Pasteur devoted himself with immense enthusiasm to science and its applications to medicine, agriculture, and industry. It was chiefly in his work on spontaneous generation and on rabies that he encountered the strongest opposition to his ideas (which were, for the time, revolutionary) from medical circles and the press. He was happy to accept the glory and honours that came his way, for he was well aware of his own value and of his scientific successes. A great friendship developed between Pasteur and the renowned British surgeon Sir Joseph Lister (1827-1912), who was quick to apply to his own discipline the discoveries of his French colleague.

The Pasteur Institute has kept its leading position it its field. It was Luc Montagnier and his collaborators at the Institute who found the HIV virus, in 1983.

Pasteur displayed no restraint in controversy. Combative an enormously self-assured, he could be devastating to the point of cruelty. He so offended one opponent, an eighty-year old surgeon, that the latter challenged him to a "duel"

Pasteur's love of animals was a byword and his concern was such that it would have provoked amusement in his colleagues were it not that it was competently real. He died with a crucifix in one hand and his wife's hand in the other.

On October 5, 1895, France honoured Pasteur's passing with a state funeral at Nôtre Dame, complete with full military honours. Temporarily placed in one of the chapels at Nôtre Dame, his body was moved in January 1896 to the resplendent funeral crypt in the Institut Pasteur where it now reposes, and where his wife was interred in 1910.

Outline of Pasteur's career
1829-1831 Student at École Primaire, Arbois
1831-1839 Student at Collège d'Arbois
1839-1842 Student at Collège Royal de Besançon
1842-1843 Student at Barbet's School and Lycée St.-Louis, Paris
1843-1846 Student at École Normale Supérieure, Paris
1846-1848 Préparateur in chemistry, École Normale
1848 September-December, Professor of physics, Lycée de Dijon
1849-1854 Professor of chemistry. Faculty of Sciences, Strasbourg
suppléant, 1849-1852
titulaire, 1852-1854
1854-1857 Professor of chemistry and dean of the Faculty of Sciences, Lille
1857-1867 Administrator and director of scientific studies, École Normale
1857-1868 Professor of geology, physics, and chemistry in their application to the fine arts, École
des Beaux-Arts, Paris
1867-1874 Professor of chemistry, Sorbonne
1867 -1888 Director of the laboratory of physiological chemistry, École Normale.
1888-1895 Director of the Institut Pasteur, Paris

Chronological outline of Pasteur's major research interests
1847-1857 Crystallography: optical activity and crystalline symmetry
1857-1865 Fermentation and spontaneous generation; studies on vinegar and wine.
1865-1870 Silkworm diseases: pébrine and flacherie
1871-1876 Studies on beer; further debates over fermentation and spontaneous generation
1877-1895 Aetiology and prophylaxis of infection diseases: anthrax, fowl cholera, swine
erysipelas, rabies

Wine is the most beautiful and most hygienic of beverages.
Études sur le vin. Part I, Chapter 2, Section B.

If the mysterious influence to which the dissymmetry of nature is due should come to change in sense or direction, the constituting elements of all living beings would take an inverse dissymmetry. Perhaps a new world would be presented to us. Who could foresee the organization of living beings, if the cellulose, which is right, should become left, if the left albumen of the blood should become right? There are here mysteries which prepare immense labours for the future, and from this hour invite the most serious meditations in science.
Lecture, Chemical Society of Paris, February 3, 1860.

All things are hidden, obscure and debatable if the cause of the phenomena is unknown, but everything is clear if its cause be known.
The Germ Theory and Its Application to Medicine and Surgery,
Chapter 2. Translated by Harold Clarence Ernst, 1856-1922

I do not forget that Medicine and Veterinary practice are foreign to me. I desire judgment and criticism upon all my contributions. Little tolerant of frivolous or prejudiced contradiction, contemptuous of that ignorant criticism which doubts on principle, I welcome with open arms the militant attack which has a method of doubting and whose rule of conduct has the motto “More light.”
The Germ Theory and Its Application to Medicine and Surgery,
Chapter 12, Section III. Translated by H. C. Ernst.

Oersted . . . suddenly saw, by chance you will say, but chance only favours the prepared mind, the needle move and take up a position quite different from the one assigned to it by terrestrial magnetism. (Le hasard favorise l’esprit preparé)
Address, December 7, 1854
Referring to Hans Christian Ørsted (1777-1851), founder of the science of electromagnetism

To be astonished of anything is the first movement of the mind towards discovery.

Two contrary laws seem to be wrestling with each other nowadays: the one, a law of blood and of death, ever imagining new means of destruction and forcing nations to be constantly ready for the battlefield – the other, a law of peace, work and health, ever evolving new means for delivering man from he scourges which beset him.
Speech opening the Pasteur Institute, Paris, November 14, 1888.
Translated by René Jules Dubos (1901-1982) in Pasteur and Modern Science.

When meditating over a disease, I never think of finding a remedy for it, but, instead, a means of preventing it.

The famous philosopher Ernest Renan (1823-1892) said of Pasteur's method of research, "This marvellous experimental method eliminates certain facts, brings forth others, interrogates nature, compels it to reply and stops only when the mind is fully satisfied. The charm of our studies, the enchantment of science, is that, everywhere and always, we can give the justification of our principles and the proof of our discoveries."

I am a man whose invincible belief is that Science and Peace will triumph over Ignorance and Warm that nations will unite, not to destroy, but to build, and that the future will belong to those who will have done most for suffering humanity.
Speech at his Golden Jubilee, December 27, 1892.
Translated by René J. Dubos in Pasteur and Modern Science.

Happy is he who bears a god within himself, an ideal of beauty, and obeys him: an ideal of art, an ideal of the virtues of the Gospel. These are the living springs of great thoughts and great actions. All are illuminated by reflections of the sublime.
Speech at his reception into the Académie Française, April 27, 1882.

The Greeks have given us one of the most beautiful words of our language, the word “enthusiasm” – a God within. The grandeur of the acts of men is measured by the inspiration from which they spring. Happy is he who bears a God within!
Speech at his reception into the Académie Française, April 27, 1882.
Translated by René J. Dubos

It is because of having reflected and studied that I have the faith of a Breton. If I had reflected and studied more, I would have attained to the faith of a Bretoness.
Pasteur's reply to a student, who asked him how, as a scientific man,
he could remain a Catholic.

If you suppress laboratories, physical science will be stricken with barrenness and death.
Some Reflections on Science in France, Part I.

Outside their laboratories, the physicist and chemist are soldiers without arms on the filed of battle. Some Reflections on Science in France, Part I.

Preconceived ideas are like searchlights which illumine the path of experimenter and serve him as a guide to interrogate nature. They become a danger only if he transforms them into fixed ideas – this is why I should like to see these profound words inscribed on the threshold of all the temples of science: “The greatest derangement of the mind is to believe in something because one wishes it to be so.”
Speech to the French Academy of Medicine, July 8, 1876.
Translated by René J. Dubos.

When, after so many efforts, you have at last arrived at a certainty, your joy is one of the greatest which can be felt by a human soul.
Speech opening the Pasteur Institute, Paris, November 14, 1888.
Translated by Mrs. R. L. Devonshire.

I am . . . most fearful of committing myself when I lack evidence. But on the contrary, no consideration can keep me from defending what I hold as true when I can rely on solid scientific proof.
Quoted by René J. Dubos in Louis Pasteur, Free Lance of Science.

To him who devotes his life to science, nothing can give more happiness than increasing the number of discoveries, but his cup of joy is full when the results of his studies immediately find practical applications.
Quoted by René J. Dubos in Louis Pasteur, Free Lance of Science.

No category of sciences exists to which one could give the name of applied sciences. There are science and the application of science, linked together as fruit is to the tree that has borne it.
Pourqui la Frane n’a pas trouvé d’hommes supérieurs au moment de péril, Section IV.

I am imbued with two deep impressions; the first, that science knows no country; the second, which seems to contradict the first, although it is in reality a direct consequence of it, that science is the highest personification of the nation. Science knows no country because knowledge belongs to humanity, and is the torch which illuminates the world. Science is the highest personification of the nation because that nation will remain the first which carries the furthest the works of thought and intelligence.
Toast at a banquet of the International Congress of Sericulture,
Milan, Italy, 1876. Translated by René J. Dubos.

It is characteristic of experimental science that it opens ever-widening horizons to our vision.
Quoted by René J. Dubos in Louis Pasteur, Free Lance of Science.

Science proceeds by successive answers to questions more and more subtle, coming nearer and nearer to the very essence of phenomena.
Études sur la bière, Chapter VI, Section vi. Translated by René J. Dubos.

The great art consists in devising decisive experiments, leaving no place to the imagination of the observer. Imagination is needed to give wings to thought at the beginning of experimental investigations on any given subject. When, however, the time has come to conclude, and to interpret the facts derived from observations, imagination must submit to the factual results of the experiments.
Quoted by René J. Dubos in Louis Pasteur, Free Lance of Science.

Young men, have faith in those powerful and safe methods, of which we do not yet know all the secrets. And, whatever your career may be, do not let yourselves be discouraged by the sadness of certain hours which pass over nations. Live in the serene peace of laboratories and libraries. Speech at his Golden Jubilee, December 27, 1892.
Translated by René J. Dubos in Pasteur and Modern Science.

One does not ask of one who suffers: What is your country and what is your religion? One merely says: You suffer, this is enough for me: you belong to me and I shall help you.
Speech at the opening of the Philanthropic Society’s Refuge for Mothers,
June 8, 1886. Translated by René J. Dubos

Physicians are inclined to engage in hasty generalizations. Possessing a natural or acquired distinction, endowed with a quick intelligence, an elegant and facile conversation . . . the more eminent they are, the less leisure they have for investigative work . . . Eager for knowledge . . . they are apt to accept too readily attractive but inadequately proven theories.
Études sur la bière, Chapter III, Section ii. Translated by René J. Dubos.

I prepare my lectures easily, and often have five whole days a week that I can devote to the laboratory. I am often scolded by Madame Pasteur, whom I console by telling her that I shall lead her to posterity.
Letter to Charles Chappuis, December 12, 1951.

I beseech you to take interest in these sacred domains so expressively called laboratories. Ask that there be more and that they be adorned for these are the temples of the future, wealth and well-being. It is here that humanity will grow, strengthen and improve. Here, humanity will learn to read progress and individual harmony in the works of nature, while humanity's own works are all too often those of barbarism, fanaticism and destruction.

"When I approach a child he inspires in me two sentiments: Tenderness for what he is, and respect for what he may become."

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