Last modified on 5 November 2014, at 04:47

Louis Pasteur

In the fields of observation chance favors only the prepared mind.

Louis Pasteur (27 December 182228 September 1895) French microbiologist, chemist, pioneer of the "Germ theory of disease", discoverer of molecular asymmetry and stereo-chemistry, and inventor of the process of Pasteurization.


I am on the edge of mysteries and the veil is getting thinner and thinner.
The idea of God is a form of the idea of the Infinite. As long as the mystery of the infinite weighs on human thought, temples will be erected for the worship of the Infinite, whether God is called Brahma, Allah, Jehovah, or Jesus
Blessed is he who carries within himself a God, an ideal, and who obeys it: ideal of art, ideal of science, ideal of the gospel virtues, therein lie the springs of great thoughts and great actions; they all reflect light from the Infinite.
Science knows no country, because knowledge belongs to humanity, and is the torch which illuminates the world.
One does not ask of one who suffers: What is your country and what is your religion? One merely says: You suffer, that is enough for me...
Let me tell you the secret that has led me to my goal. My strength lies solely in my tenacity.
  • I am on the edge of mysteries and the veil is getting thinner and thinner.
    • Letter (December 1851); as quoted in The Great Influenza: The Epic Story of the Deadliest Plague In History (2004) by John M. Barry
    • Variant translations:
      I am on the verge of mysteries and the veil is getting thinner and thinner. The nights seem to me too long... I am often scolded by Madame Pasteur, but I tell her I shall lead her to fame.
      • Microbe Hunters (1926) by Paul De Kruif
    • My plan of study is traced for this coming year... I am hoping to develop it shortly in the most successful manner... I think that I have already told you that I am on the verge of mysteries, and that the veil which covers them is getting thinner and thinner. The nights seem to me too long, yet I do not complain... I am often scolded by Mme. Pasteur, but I console her by telling her that I shall lead her to fame.
      • The Life of Pasteur (1916) by René Vallery-Radot
  • Dans les champs de l'observation le hasard ne favorise que les esprits préparés.
    • In the fields of observation chance favors only the prepared mind.
    • Lecture, University of Lille (7 December 1854)
    • Alternate translations of this or similar statements include:
      • Chance favors the prepared mind.
      • Fortune favors the prepared mind.
      • In the field of observation, chance favors the prepared mind.
      • Where observation is concerned, chance favors only the prepared mind.
  • There does not exist a category of science to which one can give the name applied science. There are sciences and the applications of science, bound together as the fruit of the tree which bears it.
    • Revue Scientifique (1871)
      • Variant translation: There are no such things as applied sciences, only applications of science.
  • L' univers est dissymetrique...
    • The universe is asymmetric and I am persuaded that life, as it is known to us, is a direct result of the asymmetry of the universe or of its indirect consequences. The universe is asymmetric.
    • Works Vol. 1 (1 June 1874) Comptes Rendus de l'Académie des Sciences
  • 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.
    • Statement of 1878, as quoted in Crystals and Life : A Personal Journey (2002) by Celerino Abad Zapatero, p. 139
  • Posterity will one day laugh at the foolishness of modern materialistic philosophers. The more I study nature, the more I stand amazed at the work of the Creator. I pray while I am engaged at my work in the laboratory.
    • As quoted in The Literary Digest (18 October 1902)
  • 'Young men, have confidence 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 become tainted by a deprecating and barren scepticism, 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. Say to yourselves first : ' What have I done for my instruction ? ' and , as you gradually advance, 'What have I done for my country?' until the time comes when you may have the immense happiness of thinking that you have contributed in some way to the progress and to the good of humanity. But, whether our efforts are or not favoured by life, let us be able to say, when we come near the great goal, ' I have done what I could.'
    • The life of Pasteur (1911), Volume II. p. 228
    • Variant translation: "Do not let yourself be tainted with a barren skepticism.", as quoted in The Louisville & Nashville Employes' Magazine Vol. 20 (1944)‎, p. 28
  • 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.
    • As quoted in Louis Pasteur, Free Lance of Science (1960) by René Jules Dubos, Ch. 3 "Pasteur in Action"
  • One does not ask of one who suffers: What is your country and what is your religion? One merely says: You suffer, that is enough for me...
    • As quoted in Louis Pasteur, Free Lance of Science (1960) by René Jules Dubos, Ch. 3 "Pasteur in Action"
  • I am utterly convinced that Science and Peace will triumph over Ignorance and War, that nations will eventually unite not to destroy but to edify, and that the future will belong to those who have done the most for the sake of suffering humanity.
    • As quoted in Louis Pasteur, Free Lance of Science (1960) by René Jules Dubos, Ch. 3 "Pasteur in Action"
  • Let me tell you the secret that has led me to my goal. My strength lies solely in my tenacity.
    • As quoted in There's a Spiritual Solution to Every Problem (2001) by Wayne W. Dyer
  • A bottle of wine contains more philosophy than all the books in the world.
    • The Mammoth Book of Zingers, Quips, and One-Liners (2004) by Geoff Tibballs
  • Science brings men nearer to God.
    • As quoted in Letter to an Atheist (2007) by Michael Patrick Leahy, p. 61
    • Original: Le premier regard de l'homme jeté sur l'univers n'y découvre que variété, diversité, multiplicité des phénomènes. Que ce regard soit illuminé par la science, — par la science qui rapproche l'homme de Dieu, — et la simplicité et l'unité brillent de toutes parts.
  • I have been looking for spontaneous generation for twenty years without discovering it. No, I do not judge it impossible. But what allows you to make it the origin of life? You place matter before life and you decide that matter has existed for all eternity. How do you know that the incessant progress of science will not compel scientists to consider that life has existed during eternity, and not matter? You pass from matter to life because your intelligence of today cannot conceive things otherwise. How do you know that in ten thousand years, one will not consider it more likely that matter has emerged from life? You move from matter to life because your current intelligence, so limited compared to what will be the future intelligence of the naturalist, tells you that things cannot be understand otherwise. If you want to be among the scientific minds, what only counts is that you will have to get rid of a priori reasoning and ideas, and you will have to do necessary deductions not giving more confidence than we should to deductions from wild speculation.
    • Parcially quoted in René Dubos, Louis Pasteur: Free Lance of Science, Da Capo Press, Inc., 1950. p 396.
    • Original in French: «La génération spontanée, je la cherche sans la découvrir depuis vingt ans. Non, je ne la juge pas impossible. Mais quoi donc vous autorise à vouloir qu'elle ait été l'origine de la vie? Vous placez la matière avant la vie et vous faites la matière existante de toute éternité. Qui vous dit que, le progrès incessant de la science n'obligera pas les savants, qui vivront dans un siècle, dans mille ans, dans dix mille ans... à affirmer que la vie a été de toute éternité et non la matière.? Vous passez de la matière à la vie parce que votre intelligence actuelle, si bornée par rapport à ce que sera l'intelligence des naturalistes futurs, vous dit qu'elle ne peut comprendre autrement les choses. Qui m'assure que dans dix mille ans on ne considérera pas que c'est de la vie qu'on croira impossible de ne pas passer à la matière? Si vous voulez être au nombre des esprits scientifiques, s, qui seuls comptent, il faut vous débarrasser des idées et des raisonnements a priori et vous en tenir aux déductions nécessaires des faits établis et ne pas accorder plus de confiance qu'il ne faut aux déductions de pures hypothèses." (Pasteur et la philosophie,Patrice Pinet, Editions L'Harmattan, p. 63.

Soirées scientifiques de la Sorbonne (1864)Edit

Address delivered by Pasteur at the "Sorbonne Scientific Soirée" (Soirées scientifiques de la Sorbonne), on April 7, 1864; in which he reported the results of his experiments refuting spontaneous generation. The original excerpt in French is found in Oeuvres de Pasteur Volume 2, (1922), Vallery-Radot, Pasteur. Paris: Masson, pp. 328-346, and is available at Gloubik
  • Great problems are now being handled, keeping every thinking man in suspense; the unity or multiplicity of human races; the creation of man 1,000 years or 1,000 centuries ago; the fixity of species, or the slow and progressive transformation of one species into another; the eternity of matter; the idea of a God unnecessary: such are some of the questions that humanity discusses nowadays.
  • Do you understand now the relationship between the question of spontaneous generation and the major problems that I listed in the beginning? But, gentlemen, in such a subject, rather than as poetry, pretty fancy and instinctive solutions, it is time for science, the true method resumes its duties and exercise. Here, it takes no religion, no philosophy, no atheism, no materialism, no spiritualism. I might even add: as a scholar, I do not mind. It is a matter of fact; I approached without a preconceived idea, too ready to declare, if the experiment had imposed upon me the confession, that there was a spontaneous generation, of which I am convinced today that those who assure it are blindfolded.
    • Original in French: Comprenez-vous maintenant le lien qui existe entre la question des générations spontanées et ces grands problèmes que j'ai énumérés en commençant? Mais, messieurs, dans un pareil sujet, assez de poésie comme cela, assez de fantaisie et de solutions instinctives; il est temps que la science, la vraie méthode reprenne ses droits et les exerce. Il n'y a ici ni religion, ni philosophie, ni athéisme, ni matérialisme, ni spiritualisme qui tienne. Je pourrais même ajouter : Comme savant, peu m'importe. C'est une question de fait; je l'ai abordée sans idée préconçue, aussi prêt à déclarer, si l'expérience m'en avait imposé l'aveu, qu'il existe des générations spontanées, que je suis persuadé aujourd'hui que ceux qui les affirment ont un bandeau sur les veux.
    • Also found in Histoire du développement de la biologie, Volume 3, by Hendrik Cornelius Dirk de Wit (1994), PPUR presses polytechniques, p. 393
  • Here is an infusion of organic matter, as limpid as distilled water, and extremely alterable. It has been prepared to-day. To-morrow it will contain animalculae, little infusories, or flakes of mouldiness. I place a portion of that infusion into a flask with a long neck, like this one. Suppose I boil the liquid and leave it to cool. After a few days, mouldiness or animalculae will develop in the liquid. By boiling, I destroyed any germs contained in the liquid or against the glass ; but that infusion being again in contact with air, it becomes altered, as all infusions do. Now suppose I repeat this experiment, but that, before boiling the liquid, I draw (by means of an enameller's lamp) the neck of the flask into a point, leaving however, its extremity open. This being done, I boil the liquid in the flask, and leave it to cool. Now the liquid of this second flask will remain pure not only two days, a month, a year, but three or four years — for the experiment I am telling you about is already four years old, and the liquid remains as limpid as distilled water. What difference is there, then, between those two vases ? They contain the same liquid, they both contain air, both are open ! Why does one decay and the other remain pure ? The only difference between them is this : in the first case, the dusts suspended in air and their germs can fall into the neck of the flask and arrive into contact with the liquid, where they find appropriate food and develop; thence microscopic beings. In the second flask, on the contrary, it is impossible, or at least extremely difficult, unless air is violently shaken, that dusts suspended in air should enter the vase; they fall on its curved neck. When air goes in and out of the vase through diffusions or variations of temperature, the latter never being sudden, the air comes in slowly enough to drop the dusts and germs that it carries at the opening of the neck or in the first curves. This experiment is full of instruction ; for this must be noted, that everything in air save its dusts can easily enter the vase and come into contact with the liquid. Imagine what you choose in the air — electricity, magnetism, ozone, unknown forces even, all can reach the infusion. Only one thing cannot enter easily, and that is dust, suspended in air. And the proof of this is that if I shake the vase violently two or three times, in a few days it contains animalculae or mouldiness. Why? because air has come in violently enough to carry dust with it. And, therefore, gentlemen, I could point to that liquid and say to you, I have taken my drop of water from the immensity of creation, and I have taken it full of the elements appropriated to the development of inferior beings. And I wait, I watch, I question it, begging it to recommence for me the beautiful spectacle of the first creation. But it is dumb, dumb since these experiments were begun several years ago; it is dumb because I have kept it from the only thing man cannot produce, from the germs which float in the air, from Life, for Life is a germ and a germ is Life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.
    • Translation from The Life of Pasteur, pp. 141-142
    • Original in French: Et par conséquent, messieurs pourrais-je dire, en vous montrant ce liquide : J’ai pris dans l’immensité de la création ma goutte d’eau, et je l’ai prise toute pleine de la gelée féconde, c’est-à-dire, pour parler le langage de la science, toute pleine des éléments appropriés au développement des êtres inférieurs, Et j’attends, et j’observe, et je l’interroge, et je lui demande de vouloir bien recommencer pour moi la primitive création ; ce serait un si beau spectacle ! Mais elle est muette ! Elle est muette depuis plusieurs années que ces expériences sont commencées. Ah ! c’est que j’ai éloigné d’elle, et que j’éloigne encore en ce moment, la seule chose qu’il n’ait pas été donné à l’homme de produire, j’ai éloigné d’elle les germes qui flottent dans l’ait" j’ai éloigné d’elle la vie, car la vie c’est le germe et le germe c’est la vie. Jamais la doctrine de la génération spontanée ne se relèvera du coup mortel que Cette simple expérience lui porte.
  • No, there is now no circumstance known in which it can be affirmed that microscopic beings came into the world without germs, without parents similar to themselves. Those who affirm it have been duped by illusions, by ill-conducted experiments, spoilt by errors that they either did not perceive or did not know how to avoid.
  • Now, gentlemen, there will be a beautiful story: what is the role, in the overall scheme of creation, of some of these little beings who are the agents of fermentation, the agents of putrefaction, of disorganization of everything that life has had in the surface of the globe. This role is immense, marvelous, really moving. Maybe one day maybe I will be given [the opportunity] to explain here some of these results. May God grant it to be still in the presence of such a brilliant assembly!
    • Original in French: Maintenant, messieurs, il Y aurait un beau sujet à traiter : c’est celui du rôle, dans l’économie générale de la création, de quelques-uns de ces petits êtres qui sont les agents de la fermentation, les agents de la putréfaction, de la désorganisation de tout ce qui a eu vie il la surface du globe. Ce rôle est immense, merveilleux, vraiment émouvant. Un jour peut-être me sera-t-il donné de vous exposer ici quelques-uns de ces résultats. Dieu veuille que ce soit encore en présence à une aussi brillante assemblée!

Discours de réception de Louis Pasteur (1882)Edit

Lecture delivered after the death of Émile Littré, when Pasteur was elected a member of the French Academy as a result. Discours de réception de Louis Pasteur, april 27, 1882.
  • To prove that, until this very day, life has never been shown to man as a product of the forces that govern matter, it could be useful the spiritual doctrine which has been very neglected elsewhere, but always finds at least a glorious refuge in your groups. Perhaps you know that in this difficult question concerning the origin of the infinitesimal, I will have brought experimental rigor that has grown weary of contradiction. Referring to the merit, however, we have inherited severe rules of the method from the great experimenters: Galileo, Pascal, Newton and their followers for two centuries.
  • The Greeks understood the mysterious power of the below things. They are the ones who gave us one of the most beautiful words in our language, the word enthusiasm. - Εν Θεος - A God within.
    • Variant translation: "The Greeks have given us one of the most beautiful words of our language, the word "enthusiasm" Εν Θεος .— a God within. The grandeur of the acts of men are measured by the inspiration from which they spring. Happy is he who bears a God within." (As quoted in Spiritual Literacy : Reading the Sacred in Everyday Life (1998) by Frederic Brussat and Mary Ann Brussat)
      • Original: Les Grecs avaient compris la mystérieuse puissance de ce dessous de choses. Ce sont eux qui nous ont légué un des plus beaux mots de notre langue, le mot enthousiasme. —Εν Θεος. — Un Dieu intérieur.
  • He who proclaims the existence of the Infinite, and none can avoid it — accumulates in that affirmation more of the supernatural than is to be found in all the miracles of all the religions; for the notion of the Infinite presents that double character that forces itself upon us and yet is incomprehensible. When this notion seizes upon our understanding we can but kneel ... I see everywhere the inevitable expression of the Infinite in the world; through it the supernatural is at the bottom of every heart. The idea of God is a form of the idea of the Infinite. As long as the mystery of the infinite weighs on human thought, temples will be erected for the worship of the Infinite, whether God is called Brahma, Allah, Jehovah, or Jesus; and on the pavement of these temples, men will be seen kneeling, prostrated, annihilated by the thought of the Infinite.
    • As quoted by Sir William Osler in his introduction to The Life of Pasteur (1907) by Rene Vallery-Radot, as translated by R .L. Devonshire (1923)
  • Where are the real sources of human dignity, freedom and modern democracy, if not in the concept of infinity to which all men are equal?
    • Original: Où sont les vraies sources de la dignité humaine, de la liberté et de la démocratie moderne, sinon dans la notion de l’infini devant laquelle tous les hommes sont égaux?
  • The greatness of human actions is measured by the inspiration that it brings. Blessed is he who carries within himself a God, an ideal of beauty and obeys it: an ideal of art, ideal of science, ideal of country, ideal virtues of the Gospel! These are the wellsprings of great thoughts and great actions. All reflections illuminate infinity.
    • Variant translations:
      • Blessed is he who carries within himself a God, an ideal, and who obeys it: ideal of art, ideal of science, ideal of the gospel virtues, therein lie the springs of great thoughts and great actions; they all reflect light from the Infinite. (As quoted by Sir William Osler in his introduction to The Life of Pasteur (1907) by Rene Vallery-Radot, as translated by R .L. Devonshire (1923)
      • Blessed is he who carries within himself a god and an ideal and who obeys it — an ideal of art, of science, or gospel virtues. Therein lie the springs of great thoughts and great actions; they all reflect light from the Infinite. (As quoted in The Wordsworth Dictionary of Quotations (1998) by Connie Robertson, p. 320)
      • Original in French: La grandeur des actions humaines se mesure à l’inspiration qui les fait naître. Heureux celui qui porte en soi un Dieu, un idéal de la beauté et qui lui obéit : idéal de l’art, idéal de la science, idéal de la patrie, idéal des vertus de l’Évangile! Ce sont là les sources vives des grandes pensées et des grandes actions. Toutes s’éclairent des reflets de l’infini.

The life of Pasteur (1902)Edit

Posthumous Biographical Book, available at Published by René Vallery-Radot, translated from the French by Mrs. R. L. Devonshire.
  • If perchance you should falter during the journey, a hand would be there to support you. If that should be wanting, God, who alone could take that hand from you, would Himself accomplish its work.
    • p. 19
  • "Though one discovery always surpasses another, and though the chemical and physical knowledge accumulated since his time has gone beyond all Lavoisier's dreams, his work, like that of Newton and a few other rare spirits, will remain ever young. Certain details will age, as do the fashions of another time, but the foundation, the method, constitute one of those great aspects of the human mind, the majesty of which is only increased by years."
  • God grant that by my persevering labours I may bring a little stone to the frail and ill-assured edifice of our knowledge of those deep mysteries of Life and Death where all our intellects have so lamentably failed.
    • p. 114
  • I confess frankly, however, that I am not competent on the question of our philosophical schools. Of M. Comte I have only read a few absurd passages; of M. Littré I only know the beautiful pages you were inspired to write by his rare knowledge and some of his domestic virtues. My philosophy is of the heart and not of the mind, and I give myself up, for instance, to those feelings about eternity which come naturally at the bedside of a cherished child drawing its last breath. At those supreme moments, there is something in the depths of our souls which tells us that the world may be more than a mere combination of phenomena proper to a mechanical equilibrium brought out of the chaos of the elements simply through the gradual action of the forces of matter.
    • p. 163
  • You say that, in the present state of science, it is wiser to have no opinion: well, I have an opinion, not a sentimental one, but a rational one, having acquired a right to it by twenty years of assiduous labour, and it would be wise in every impartial mind to share it. My opinion — nay more, my conviction— is that, in the present state of science, as you rightly say, spontaneous generation is a chimera ; and it would be impossible for you to contradict me, for my experiments all stand forth to prove that spontaneous generation is a chimera. What is then your judgment on my experiments? Have I not a hundred times placed organic matter in contact with pure air in the best conditions for it to produce life spontaneously? Have I not practised on these organic materia which are most favourable, according to all accounts, to the genesis of spontaneity, such as blood, urine, and grape juice? How is it that you do not see the essential difference between my opponents and myself? Not only have I contradicted, proof in hand, every one of their assertions, while they have never dared to seriously contradict one of mine, but, for them, every cause of error benefits their opinion. For me, affirming as I do that there are no spontaneous fermentations, I am bound to eliminate every cause of error, every perturbing influence, I can maintain my results only by means of most irreproachable experiments; their opinions, on the contrary, profit by every insufficient experiment and that is where they find their support."
      • Original in French from Œuvres de Pasteur, Volume 7 (1939), Masson et cie, p. 539: Mon opinion, mieux encore, ma conviction, c'est que, dans l'état actuel de la science, comme vous dites avec raison, la génération spontanée est une chimère, et il vous serait impossible de me contredire, car mes expériences sont toutes debout, et toutes prouvent que la génération spontanée est une chimère


  • The more I know, the more nearly is my faith that of the Breton peasant. Could I but know all I would have the faith of a Breton peasant woman.
    • As quoted in "Louis Pasteur" in The Catholic Encyclopedia (1913)
    • Variant: I have the faith of a Breton peasant and by the time I die I hope to have the faith of a Breton peasant's wife.
      • As quoted in Letter to an Atheist (2007) by Michael Patrick Leahy, p. 61
    • His descendents, Louis-Pasteur Vallery-Radot, and Maurice Vallery-Radot disputed the authenticity of such statements. According to Maurice Vallery-Radot, Pasteur (1994), p. 378, the attributed assertion first appeared in the Semaine religieuse .... du diocèse de Versailles (6 October 1895), p. 153, shortly after the death of Pasteur.
  • When I approach a child, he inspires in me two sentiments; tenderness for what he is, and respect for what he may become.
    • The phrase in French is found in Étienne Blanchard (1941), "Recueil d'idées", p. 76: "Quand je m'approche d'un enfant, il m'inspire deux sentiments: la tendresse pour ce qu'il est, et le respect pour ce qu'il peut être un jour." It doesn't give any reference, just like modern books which include the quote in English.


  • It is surmounting difficulties that makes heroes.
    • Lajos Kossuth (also known as Louis Kossoth), as quoted in Human Development in Action (1942) by University of California, and The Forbes Book of Business Quotations (1997) by Edward C. Goodman and Ted Goodman.
  • A little science estranges men from God, but much science leads them back to Him.
    • This is attributed to Pasteur in God Doesn't Believe in Atheists (2002) by Ray Comfort, but it seems to be simply a paraphrase of Francis Bacon, in "On Atheism" in Essays (1597): A little Philosophy inclineth Mans Minde to Atheisme; But depth in Philosophy, bringeth Mens Mindes about to Religion.

Quotes about PasteurEdit

  • Pasteur was far ahead of his time. Although the structural theory of Kekulé had not yet been proposed, Pasteur explained his results by speaking of the molecules themselves, saying, “There is no doubt that [in the dextro tartaric acid] there exists an asymmetric arrangement having a nonsuperimposable image. It is no less certain that the atoms of the levo acid have precisely the inverse asymmetric arrangement.” Pasteur’s vision was extraordinary, for it was not until 25 years later that his ideas regarding the asymmetric carbon atom were confirmed.
    Today, we would describe Pasteur’s work by saying that he had discovered enantiomers. Enantiomers, also called optical isomers, have identical physical properties, such as melting point and boiling point, but differ in the direction in which their solutions rotate plane-polarized light.
    • John McMurry, Organic Chemistry 8th ed. (2012), Ch. 5. Stereochemistry at Tetrahedral Centers
  • Pasteur originally conceived the idea of germs and of destroying them. Although this started as a personal thing, it has mushroomed into DDT, killing beetles and worms, resulting in food contamination, much sickness, and trouble. Although he is regarded as hero by modern medicine, Pasteur will be treated in much the same way as a warmonger when he is judged in the spiritual world.

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