Swan-necked flasks in which boiled broth stayed clear for months although open to the air (1859)
Pasteur's demonstration that life does not arise spontaneously ā dust, not air, carries the organisms
Science Ā· Medicine & the body
Germ theory
Established 1860sā1880s
Medicine ā microbiology and public health
The idea that many diseases are caused by specific microorganisms invading the body, which displaced the ancient belief that illness came from miasma ā foul air rising from filth. Suggested as early as 1546 by Girolamo Fracastoro, it became demonstrable only in the nineteenth century, when Louis Pasteur destroyed the doctrine of spontaneous generation with his swan-necked flasks and Robert Koch tied particular bacteria to anthrax, tuberculosis and cholera. It transformed surgery through Lister's antisepsis, obstetrics through Semmelweis's handwashing, and cities through sanitation.
How to spot them
- āøThe theory that replaced miasma ā the belief that disease came from bad air
- āøPasteur's swan-necked flasks and Koch's postulates are the two set-piece demonstrations
- āøKoch found the bacteria of anthrax (1876), tuberculosis (1882) and cholera (1883)
- āøSemmelweis in Vienna, Snow in Soho, Lister in Glasgow ā the practical consequences
- āøKoch won the 1905 Nobel Prize in Physiology or Medicine
Key facts
Four postulates for proving that a particular organism causes a particular disease
Koch's postulates: found in every case, isolated in pure culture, reproducing the disease, and re-isolated
The anthrax bacillus in 1876, the tubercle bacillus in 1882, the cholera vibrio in 1883 (1882)
Robert Koch's run of identifications; he announced the tubercle bacillus on 24 March, now World TB Day
Chlorinated lime at the door of a Viennese maternity ward in 1847 (1847)
Ignaz Semmelweis cut deaths from puerperal fever dramatically, and was ignored
A carbolic acid spray over the operating table at Glasgow Royal Infirmary from 1867 (1867)
Joseph Lister's antiseptic surgery, prompted by reading Pasteur
The removal of a pump handle in Broad Street, Soho, in 1854 (1854)
John Snow's cholera investigation, the founding case of epidemiology
The 'seminaria contagionum' proposed in a Veronese book of 1546 (1546)
Girolamo Fracastoro's seeds of contagion ā three centuries ahead of the evidence
Silkworms dying of muscardine in Lombardy, traced to a fungus in 1835 (1835)
Agostino Bassi's work, the first disease shown to be caused by a living organism
Key ideas
- The decisive move was specificity: not merely that microbes cause disease, but that one particular organism causes one particular disease, which is what Koch's postulates formalise.
- Pasteur's flask experiment worked because the bend, not a plug, excluded dust ā air could still reach the broth, so the result could not be blamed on excluding a vital principle.
- Practice ran ahead of theory. Semmelweis had no idea what he was washing off, and Snow could not see the cholera bacillus, but both acted correctly on the pattern of the evidence.
Quick-fire facts
- ā¢It displaced miasma theory, which held that disease arose from bad air ā the origin of the word malaria
- ā¢Girolamo Fracastoro proposed transmissible 'seeds of contagion' in 'De Contagione' (1546)
- ā¢Agostino Bassi showed in 1835 that a fungus caused muscardine in silkworms
- ā¢Ignaz Semmelweis introduced handwashing in chlorinated lime at the Vienna General Hospital in 1847; his colleagues rejected the idea and he died in an asylum in 1865
- ā¢John Snow mapped cholera deaths around the Broad Street pump in 1854 and had the handle removed
- ā¢Louis Pasteur's swan-neck flask experiments of 1859ā64 refuted spontaneous generation; pasteurisation followed in 1865
- ā¢Joseph Lister introduced carbolic acid antisepsis in Glasgow in 1867, publishing in The Lancet
- ā¢Robert Koch worked out the anthrax life cycle in 1876, identified Mycobacterium tuberculosis in 1882 and Vibrio cholerae in 1883
- ā¢Koch's postulates were formalised with Friedrich Loeffler; they do not cover asymptomatic carriers or viruses
- ā¢Koch's laboratory gave us solid agar culture media, suggested by Fanny Hesse, and the dish named after Julius Richard Petri
- ā¢Robert Koch received the 1905 Nobel Prize in Physiology or Medicine; Pasteur died in 1895, before the prizes began
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Sources
- Institut Pasteur ā History of the Institut Pasteur
- The Nobel Foundation ā The Nobel Prize in Physiology or Medicine 1905