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f, on a sunny day, you sit near a window in a darkened room andfollow a beam of light streaming in, you can observe particles of dust reflecting the sunlight into your eye. The microbial content of these small

pieces of ‘floating matter’ is well knownto many of us, which is why we work bya Bunsen flame. However, the develop-ment of methods to ‘see’ the particulatecontents of the air and analyse itsconstituents helped resolve someimportant issues of late 19th centurybiological science.

John TyndallThe man who exploited light and dustto advance biology was not in fact abiologist, but rather an Irish physicistand science popularizer called JohnTyndall (Fig. 1). He worked at the RoyalInstitution in London and had pub-lished scientific works on heat, lightand sound, as well as popular books

Iand lectures. For some of his experi-ments on light and gases he needed tocleanse the air of particles and sodeveloped a completely novel way toassay the purity of air. ‘The eye being keptsensitive by darkness’, Tyndall reported,‘a concentrated beam of light was found tobe a most searching test for suspendedmatter – a test indeed indefinitely moresearching than that furnished by the mostpowerful microscope’. Using his newpiece of equipment, which relied onobserving light scattered by dustparticles, Tyndall quickly made a seriesof important observations on theproperties of the ‘floating matter’ of air.

Dust and diseaseHe presented this work in January 1870in a lecture to the Royal Institutionentitled Dust and disease. Here, he firstreported experiments demonstratingthat dust was mainly composed oforganic matter, something he had not

� The summit of Mont Blanc, French Alps. O.T. Chamonix No. 120 / M. Colonel

� Fig. 1. Carte de visite of John Tyndall takenduring his lecturing tour of the USA in1872–1873. Author’s collection

164 microbiology today nov 05

Back in the 1870s, opinion was divided on

whether microbes could arise in growth media

from nowhere. Gavin Thomas describes how

this theory was disproved by an Irish physicist

and science popularizer called John Tyndall.

Microbes in the air: John Tyndall andthe spontaneous

generation debate

microbiology today nov 05 167

tion, so he decided to address this topicdirectly, becoming embroiled in adebate which was to occupy him for the next 7 years of his life.

Tyndall’s chamberThe most famous piece of apparatusdeveloped by Tyndall during thisperiod was a wooden chamber that was key in demonstrating the causal linkbetween the presence of dust and thesubsequent growth of microbes inliquid broth (Fig. 2). The chamber hada glass front, small side windows and aback door. A pair of thin glass tubes wasinserted in the top, bent in a way to pre-vent passage of dust from the outside.Test tubes were sealed into the base,open to the chamber above, and therewas a movable pipette that pierced thetop and could be used to add mediumto the flasks. The walls of the chamberwere coated in glycerine, which waseffective at binding and holding the dust particles. Tyndall would seal thesechambers and shine light through theside windows to follow the settling ofdust particles until they had vanishedfrom the beam. Culture medium wasthen added to the test tubes via thepipette and a vat of boiling oil wasbrought up underneath to sterilizethem. The chamber was then left to seeif anything would grow in the testtubes; Tyndall did hundreds of theseexperiments with different infusionswhere he would see no growth. Thechamber was open to the air, so it couldnot be argued that some other elementof the air was required for growth;rather it clearly demonstrated that whenparticles were absent from the air, thetest tubes would remain sterile.

To the mountainsTyndall was also a mountaineer of somerepute, being drawn to the Alps in 1856to study glaciers with Thomas HenryHuxley. He grew to love the Alps as they

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anticipated. He then demonstrated,using his light scattering assay, that airfiltered by cotton wool was ‘opticallyempty’, meaning that the path of thebeam appeared black, which he alsosaw with air that had been left to settlefor long periods of time in a sealed glass chamber. Finally, he reported that his own breath, especially the endof his expiration, was remarkably free offloating matter. He had recently beentaken by Lister’s methods for antisepticsurgery, which argued that infectionspreads through the air due to themicrobes contained within it and view-ed his data as entirely consistent withthese. Hence, Tyndall extrapolated hisconclusions to make a strong state-ment in favour of the germ theory ofdisease; an idea which had not yetfound acceptance with the majority ofthe English medical profession.

Following Tyndall’s 1870 lecture,there was much criticism of his con-clusions from prominent physicianswho believed that ideas relating to thenature of disease ‘pertain most to the biologist and the physician’ and that aphysicist should know better the factsof epidemic disease before delving intothe living world. The pathologist Charl-ton Bastian confronted Tyndall directlyin a series of letters to The Times, playingdown the evidence supporting germtheory and discussing his own experi-ments which disagreed with previouswork by Pasteur, Lister and the like.Bastian then published a 1,115-pagebook in 1872 describing many experi-ments that he argued proved that micro-bial growth could occur in conditions inwhich Pasteur would claim they shouldnot, i.e. after boiling of a sealed liquidgrowth medium for 30 minutes. Bastianconcluded from his experiments that‘life arises de novo in animal and vegetableinfusions’. This agitated Tyndall, whowas a strong believer in Pasteur’s experi-ments disproving spontaneous genera-

provided him with an annual escape from the rigours ofscience, and he quickly became an accomplished mount-aineer, climbing Mont Blanc in 1857 and later being the first toclimb the Weisshorn in 1861. This was not without its dangersand in 1858 when solo climbing Monte Rosa he dropped hisice axe at the summit and had to watch it slide away towardsthe mountain edge. The descent would have been impossiblewithout the axe, but fortunately it stopped before reaching thedrop and Tyndall was able to make his descent successfully.

Tyndall took a series of ‘infusions’ with him to the Alps whichhe had prepared at the Royal Institution. These were glassflasks shaped as in Fig. 3 containing liquid broth which hadbeen boiled and then sealed by heating the glass and drawingout the end until it was fused. He took about 50 of these flasks,which contained infusions of beef, mutton, turnip and cucum-ber, to perform a series of experiments one summer whilestaying at his cottage on the Bel Alp. Tyndall had demonstratedthat upon opening these flasks there was a brief inrush of air,but that the shape of the neck prevented any further entry ofparticulate matter. He opened half of them in a hayloft near hiscottage and the other half on a ledge overlooking the Aletschglacier, making sure he was himself downwind of the flasksand using a spirit lamp to sterilize the steel pliers that were usedto break off the top of the flask. Tyndall then incubated all hisopened flasks over his kitchen stove for 3 days and found thatall but two of the flasks opened in the hayloft were ‘invaded by organisms’, while not one opened in the ‘cleaner vivifyingmountain air’ had any growth. Tyndall hence demonstratedthat air from the mountain top was largely free from organicmaterial and no life was produced in the flasks, while the flasksopened in the closed environment of the hayloft, in thepresence of an abundance of organic material, almost alwayshad growth. This particular experiment was a continuation ofan earlier demonstration by Pasteur that air from the Mer deGlace was cleaner than that from the town below, but wastypical of the many experiments Tyndall performed during the1870s to provide convincing quantitative evidence supportingthe spread of microbes in the air.

A bale of hay Tyndall’s experiments hit difficulties in 1876 when, for a reasonthat eluded him, he could no longer keep his infusions sterile.He only managed to reproduce his experiments again aftermoving his lab to Kew Gardens. Earlier in 1876 Tyndall hadmet the German botanist Ferdinand Cohn, who discussed hisrecent description of spores in the life-cycle of the hay bacillus(Bacillus subtilis) and also mentioned Robert Koch’s observa-tions of spore formation in B. anthracis. Tyndall had brought abale of hay into the Royal Institution at about the time that his

experiments became contaminated and he reasoned thatspores from the hay were now in the air of his lab and were ableto survive the heating process he used to sterilize his infusions.

It is of interest to note that this had been observed pre-viously by Bastian, who had used these data to support hisideas of spontaneous generation. Now, however, Tyndall had a potential explanation and investigated the heat resistance ofspores in more detail. After a few months of work he discover-ed that a series of boiling and cooling steps in the treatment ofhis growth medium could completely prevent any growth inhis flasks. By heating and cooling the spores were germinatingand were then being killed during the next exposure to boil-ing. This process of fractional sterilization, sometimes knownas Tyndallization, is still used today to sterilize certain diag-nostic growth media that cannot tolerate autoclaving.

By 1880 the debate was effectively over due to the hardwork of Tyndall and others, including the EnglishmenWilliam Dallinger and John Drysdale, who had demonstratedthat Bastian’s experiments could be explained simply byimproved knowledge of microbiology and did not need toimply continual de novo creation. Spontaneous generationwas removed from the frontlines of science into the historybooks – all started by a chance observation made whilepursuing a completely different field of science.

Gavin H. ThomasLecturer in Molecular Microbiology, Department of Biology, Area 10, University of York, PO Box 373, York YO10 5YW, UK (t01904 328678; f01904 328825; eght2@york.ac.uk)

Further readingFleming, F. (2001). Killing Dragons: The Conquest of the Alps.London, New York: Granta Books.

Strick J. E. (2000). Sparks of Life. Darwinism and the VictorianDebates over Spontaneous Generation. Cambridge, London: HarvardUniversity Press.

Tyndall, J. (1881). Essays on the Floating Matter in the Air in Relationto Putrefaction and Infection. London: Longmans Green.

Worboys, M. (2000). Spreading Germs. Disease Theories of MedicalPractice in Britain, 1865–1900. Cambridge: CUP.

AcknowledgementsTyndall’s tubes and chamber will be available for general viewing at the Royal Institution after a major redevelopment due to becompleted by the end of 2007. The author would like to thankProf. Frank James and Katharine St Paul for locating the chamberand for allowing it to be photographed, and Prof. James Strick for comments on this article.

� Fig. 2. A surviving chamber tracked down in the archivesof the Royal Institution. Gavin Thomas

� Fig. 3. Flasks containing various different infusionsrecovered from Tyndall’s chalet in the Bel Alp now at the Royal Institution. Gavin Thomas

� The Mer de Glace, Chamonix, France.O.T. Chamonix No. 99 / F.E. Cormier

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