Louis Pasteur Quotes

As quoted in Louis Pasteur, Free Lance of Science (1960) by René Jules Dubos, Ch. 3 : Pasteur in Action

As quoted in "Louis Pasteur" in The Catholic Encyclopedia (1913)
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.
Disputed
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.

This is misattributed to Pasteur in multiple sources. Usually used as a proof that he had recanted germ theory, but also appears in scientific literature. Actual quote is from Claude Bernard, a contemporary of Pasteur who disagreed with germ theory. "The Terrain Within: A Naturalistic Way to Think" (2012). "Louis Pasteur, and the Myth of Pasteurization" (2013).
Misattributed
Source: Lets Talk Nutrition, Lets Talk Nutrition, en-US, 2017-01-27 http://letstalknutrition.com/the-terrain-within-a-naturalistic-way-to-think/,

Partially 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.
Context: 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 understood 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.

The life of Pasteur (1911), Volume II http://archive.org/stream/lifeofpasteurtra02valluoft/lifeofpasteurtra02valluoft_djvu.txt. 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

As quoted in Louis Pasteur, Free Lance of Science (1960) by René Jules Dubos, Ch. 3 "Pasteur in Action"

Revue Scientifique (1871)
Variant translation: There are no such things as applied sciences, only applications of science.

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.

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 Life of Pasteur (1902)
Context: 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.

As quoted in Louis Pasteur, Free Lance of Science (1960) by René Jules Dubos, Ch. 3 "Pasteur in Action"
As quoted in Louis Pasteur, Free Lance of Science (1960) by René Jules Dubos, Ch. 3 "Pasteur in Action"
Context: 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.

Translation from The Life of Pasteur, pp. 141-142 https://archive.org/stream/cu31924012227595#page/n153/mode/2up
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.
Soirées scientifiques de la Sorbonne (1864)
Context: 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.

Partially 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.
Context: 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 understood 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.

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!
Soirées scientifiques de la Sorbonne (1864)

Discours de réception de Louis Pasteur (1882)

L' univers est dissymetrique...
Works Vol. 1 (1 June 1874) Comptes Rendus de l'Académie des Sciences

Discours de réception de Louis Pasteur (1882)
Context: The human spirit, driven by an invincible force, will never cease to ask: What is beyond? Does he want to stop either in time or in space? Since the point at which he has reigned is only a finite magnitude, greater only than all those who have preceded him, he has scarcely begun to think of it as the implacable question and always without being able to silence his curiosity. There is nothing to answer: there are spaces, times or magnitudes without limits. No one understands these words. <!-- He who proclaims the existence of the infinite, and no one can escape from it accumulates in this affirmation more supernatural than there is in all the miracles of all religions; for the notion of the infinite has the double character of imposing itself and of being incomprehensible.

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
Soirées scientifiques de la Sorbonne (1864)
Context: 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.

As quoted in The Literary Digest (18 October 1902)
Context: 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.

Source: The Life of Pasteur (1902), p. 163
Context: 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.

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
Soirées scientifiques de la Sorbonne (1864)
Context: 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.

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)
Discours de réception de Louis Pasteur (1882)
Context: 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.

Source: The Life of Pasteur (1902), p. 163
Context: 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.

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)
Discours de réception de Louis Pasteur (1882)
Context: 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.

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 Life of Pasteur (1902)
Context: 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.

Partially 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.
Context: 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 understood 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.

The Mammoth Book of Zingers, Quips, and One-Liners (2004) by Geoff Tibballs

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.
Misattributed

Discours de réception de Louis Pasteur (1882)
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?

Translation from The Life of Pasteur p. 142 https://archive.org/stream/cu31924012227595#page/n155/mode/2up
Soirées scientifiques de la Sorbonne (1864)

Translation from The Life of Pasteur, p. 140 https://archive.org/stream/cu31924012227595#page/n153/mode/2up
Soirées scientifiques de la Sorbonne (1864)

Source: The Life of Pasteur (1902), p. 19

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.
Disputed

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.
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.

Answer from Pasteur to his disciple Elie Metchnikoff when was questioned whether his approach to spontaneous generation was bound to a religious ideal. According to Patrice Debré's Luis Pasteur, 2000 https://books.google.co.uk/books?id=RzOcl-FLw30C&lpg=PP1&pg=PA176#v=onepage&q&f=false,, p. 176.
Disputed

The Life of Pasteur (1902)

This alleged quotation is attributed to Pasteur at least as early as 1952, in Miracles, by Morvan Lebesque. It appears in a letter about Pasteur reprinted in the February 7, 1920 issue of America magazine, but the author of the letter attributes the saying to Pascal and says it applies to Pasteur. It may be 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.
Misattributed

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.
Discours de réception de Louis Pasteur (1882)

Source: The Life of Pasteur (1902), p. 242; The first statement in bold in the above paragraph, as quoted from in Œuvres de Pasteur, Volume 7 (1939), Masson et cie, p. 539 reads:
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

Discours de réception de Louis Pasteur (1882)

Soirées scientifiques de la Sorbonne (1864)
Original: (fr) 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.

Original: (fr) 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."

As quoted in Pasteur et la philosophie (2004), by Patrice Pinet, p. 63

Partially quoted in Louis Pasteur : Free Lance of Science (1950) by René Dubos, p 396