Pasteur: swan-neck flasks and the memoir on organized corpuscles in the atmosphere

1859-1862 Life and health method

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An experiment with flasks whose long neck is bent: air entered freely, but dust settled in the bend and the broth stayed sterile; once the neck was broken off, the broth turned cloudy.

The experiments were set up by the Frenchman Louis Pasteur in reply to Pouchet's Hétérogénie (1859) and to a competition of the Academy of Sciences: the Alhumbert prize, whose question was to 'attempt, by well-conducted experiments, to throw new light on the question of spontaneous generation'. The Academy awarded the prize to Pasteur in 1862, and the 1864 commission again ruled in his favour.

Historians still debate how purely experimental the Academy's decision was.

Why this date

memoir 1861, printed 1862, Alhumbert prize 1862. high: experiments from 1859, memoir presented to the Academy 1861, published in Annales de chimie et de physique, 3rd ser., vol. 64 (1862)

What it grew from

• Needham (1748) and Spallanzani (1765): infusions, boiling and sealed flasks

  influenced · Confidence: medium

  Pasteur continued Spallanzani's line (boiling in flasks), adding protection from dust with free access of air, which removes Needham's main objection about the "spoiled" air in sealed flasks.

  Dispute: Parke describes Pasteur's experiments directly as a continuation of Spallanzani's line ("continued along these lines"). What remains unsourced is only the methodological detail that the purpose of the curved neck was precisely to remove Needham's objection about spoiled air.

  Link sources

  • Parke E. C. «Flies from meat and wasps from trees: Reevaluating Francesco Redi's spontaneous generation experiments», Studies in History and Philosophy of Biological and Biomedical Sciences 45, 34-42 (2014) Verified 25 Sep 2026

    In the eighteenth century, Lazzaro Spallanzani did experiments demonstrating that infusoria do not grow in sterilized flasks. In the nineteenth century Pasteur continued along these lines, showing that microscopic life forms are not spontaneously generated in vessels of sterilized liquid, but rather get there by contamination through exposure to microbes in the surrounding air (Pasteur, 1864).

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Fermentation as a reproducible practice: beer, bread, wine

  influenced · Confidence: medium

  Pasteur came to the study of microorganisms from a practical problem about fermentation: in 1856 he went regularly to a beetroot alcohol works in Lille to find out why the product was failing, and from fermentation he moved to the controversy over spontaneous generation, for which the flask experiments were made.

  Dispute: In the Dictionary of Scientific Biography Geison writes that Pasteur's interest in fermentation has often been traced to the brewing and distilling industry of Lille, and immediately gives Pasteur's own objection: he traced his interest to 1849 and to Biot's report that amyl alcohol was optically active. The practical problem was certainly there; what is disputed is its role in the conception of the work.

  Link sources

  • Geison G. L. «Pasteur, Louis», Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

    During 1856, he went regularly to the beetroot alcohol factory of M. Bigo, seeking the cause of and remedies for recent disappointments in the quality of that product.

  • Geison G. L. «Pasteur, Louis», Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

    For this reason especially, Pasteur's interest in fermentation has often been traced to the brewing industry in Lille. Pasteur, however, traced his interest to 1849, when Biot informed him that amyl alcohol displayed optical activity.

  • Geison G. L. «Pasteur, Louis», Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

    From crystallography and structural chemistry Pasteur moved to the controversial and interrelated topics of fermentation and spontaneous generation.

  • Geison G. L. «Pasteur, Louis», Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

    Pasteur's biological theory of fermentation virtually implied a biological or 'germ' theory of disease.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Pasteur: fermentation is the physiological work of living cells, from the Bigo factory to the Études sur la bière

  influenced · Confidence: medium

  Pasteur came to spontaneous generation out of fermentation: if each fermentation is carried out by its own organism introduced from outside, the question of where that organism comes from is the next one. His biographer calls the two topics interrelated.

  Dispute: The quotation asserts that the topics are interrelated and the order of the move, but does not analyse what exactly from the fermentation work was needed in the flask experiments. No fuller statement of the link by a historian was found, hence medium confidence.

  Link sources

  • Geison G. L. «Pasteur, Louis», Complete Dictionary of Scientific Biography (via Encyclopedia.com) (2008) Verified 20 Sep 2026

    From crystallography and structural chemistry Pasteur moved to the controversial and interrelated topics of fermentation and spontaneous generation.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

What grew out of it

• Lister: the antiseptic principle in surgery (as an outgrowth of the refutation of spontaneous generation)

  influenced · Confidence: high

  The refutation of spontaneous generation yielded a method: the sterilization and aseptic techniques on which bacteriology grew, and Lister's antiseptic principle.

  Link sources

  • Britannica, Louis Pasteur: Spontaneous generation (2024) Verified 20 Sep 2026

    This not only settled the philosophical problem of the origin of life at the time but also placed on solid ground the new science of bacteriology, which relied on proven techniques of sterilization and aseptic manipulation.

  • Lister J. On the Antiseptic Principle in the Practice of Surgery (1867), DePaolo, Victorian Web (1867) Verified 5 Oct 2026

    But when it had been shown by the researches of Pasteur that the septic property of the atmosphere depended, not on the oxygen or any gaseous constituent, but on minute organisms suspended in it, which owed their energy to their vitality, it occurred to me that decomposition in the injured part might be avoided without excluding the air, by applying as a dressing some material capable of destroying the life of the floating particle.

  • Britannica, History of medicine: Verification of the germ theory (2024) Verified 20 Sep 2026

    From Pasteur, British surgeon and medical scientist Joseph Lister derived the concepts that enabled him to introduce the antiseptic principle into surgery.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Other links

• The doctrine of spontaneous generation in Aristotle's "Generation of Animals"

  refuted by · Confidence: high

  Pasteur's flask experiments showed that with dust fully excluded a boiled medium stays sterile, and this is regarded as the refutation of spontaneous generation.

  Dispute: Three lines of dispute. (1) Farley and Geison (1974) argued that Pasteur's success was secured by the political and ideological backing of the Academy, and that Pouchet's experiments were no worse; Roll-Hansen (2018) objects: "It was on the conduct of these experiments that the Academy made judgements favorable to Pasteur". (2) Strick (2000) shows that neither the swan-necked flasks nor the dust-free box experiments were regarded as crucial experiments by many authors for a long time, at least into the 1880s (paraphrase; not checked verbatim against the book); in Britain the dispute with Bastian continued until Tyndall's work on heat-resistant spores (1876-1877). (3) Pasteur himself saw the refutation of spontaneous generation as a precondition for germ theory: "He was convinced that his germ theory could not be firmly substantiated as long as belief in spontaneous generation persisted" (Britannica). (4) Pasteur's exemplary case of the doctrine was van Helmont's mice "recipe" (1648), which he dissected in his Sorbonne lecture of 7 April 1864; no verbatim quotation of the lecture has been extracted, and the van Helmont link rests on a paraphrase (Zarka).

  Link sources

  • Britannica, Louis Pasteur: Spontaneous generation (2024) Verified 20 Sep 2026

    These experiments proved that there was no spontaneous generation, since the boiled broth, if never reexposed to air, remained sterile.

  • SEP, Life (2023) Verified 20 Sep 2026

    Two centuries of experiments and debates overturned this view. Louis Pasteur's abiogenesis experiments illustrated that life does not typically come from non-life.

  • Pasteur L. Des générations spontanées; Zarka Y. Pasteur face au dogme de la génération spontanée (Meer) (1864)

    Je vais vous montrer, mesdames et messieurs, par où les souris sont entrées (...)

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

  Further reading

  Not evidence: these carry no quotation and support nothing we wrote. They are books and scans to read next.

  • Farley J., Geison G. L. «Science, Politics and Spontaneous Generation in Nineteenth-Century France: The Pasteur-Pouchet Debate», Bulletin of the History of Medicine 48 (2), 161-198 (1974)
  • Roll-Hansen N. «Revisiting the Pouchet-Pasteur controversy over spontaneous generation: understanding experimental method», History and Philosophy of the Life Sciences 40, 68 (2018)
  • Strick J. E. «Sparks of Life: Darwinism and the Victorian Debates over Spontaneous Generation», Harvard University Press (2000)

Node sources

• Louis Pasteur: Spontaneous generation (Britannica) (2024) Verified 20 Sep 2026

  He showed that beef broth could be sterilized by boiling it in a "swan-neck" flask, which has a long bending neck that traps dust particles and other contaminants before they reach the body of the flask. However, if the broth was boiled and the neck of the flask was broken off following boiling, the broth, being reexposed to air, eventually became cloudy, indicating microbial contamination.

• Roll-Hansen N. Revisiting the Pouchet-Pasteur controversy over spontaneous generation: understanding experimental method. Hist. Phil. Life Sci. 40(4): 68 (2018) Verified 20 Sep 2026, quotation assembled from fragments

  Farley and Geison (Bull Hist Med 48:161-198, 1974) told a counter-story of how Pasteur's success was due to political and ideological support rather than superior experimental science. They claimed that Pasteur violated proper norms of scientific method, and that the French Academy of Science did not see this, or did not want to... I argue that the core of the scientific debate was not general theories for or against spontaneous generation but the outcome of specific experiments. It was on the conduct of these experiments that the academy made judgements favorable to Pasteur.

"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong. "Assembled from fragments" means the words do not stand together on the page: we found each fragment separately and joined them with an ellipsis.

Further reading

Not evidence: these carry no quotation and support nothing we wrote. They are books and scans to read next.

• Pasteur L. Mémoire sur les corpuscules organisés qui existent dans l'atmosphère: examen de la doctrine des générations spontanées. Annales de chimie et de physique, 3e sér., t. 64 (Wellcome Collection) (1862)
• Farley J., Geison G.L. Science, politics and spontaneous generation in nineteenth-century France: the Pasteur-Pouchet debate. Bull. Hist. Med. 48: 161-198 (1974)
• «Prix Alhumbert pour l'année 1862. Rapport sur ce concours fait dans le comité secret de la séance du 1er décembre», Comptes rendus des séances de l'Académie des sciences 55, 977-979 (1862)
• Pouchet F. A. «Hétérogénie ou traité de la génération spontanée», Paris: J.-B. Baillière (1859)

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