tyndall experiment in microbiology

Hektoen International

A Journal of Medical Humanities

John Tyndall, FRS: The beauty of science

JMS Pearce Hull, England, United Kingdom

Over many centuries non-medical people have carried out research into disease and its causes, often making important advances. The 1841 Census estimates suggest a third of all medical practitioners in England were unqualified. a The great scientist John Tyndall (1820–1893) (Fig 1) was not a medical practitioner, but an Irish physicist, natural philosopher, and mountaineer whose work greatly advanced medical science. 2, 3 As a scientist, Tyndall saw beauty not only in the colorful Alpine skies, but also in the deeper scientific processes that produced them.

Tyndall was born on 2 August 1820 at Leighlinbridge, County Carlow, son of John Tyndall, a shoemaker, and Sarah Macassey. After humble beginnings, he later forged friendships with the famous Thomas Huxley and Michael Faraday, which founded a career distinguished by scientific discoveries. He successfully investigated many unsolved mysteries of the natural world, and skillfully disseminated scientific knowledge to the public.

As one instance, Tyndall wondered: why is the sky blue and the sunset red? He guessed that light was scattered by dust particles. To test this hypothesis he placed a few drops of milk into a long tank of water and shone a bright light through one side. He observed that the cloudy water appeared blue near the light, but beyond that it became orange, and at the far side of the tank was red. He deduced that the blue light had been scattered by the tiny milk particles (the “Tyndall effect”) close to the light source; red light having a longer wavelength appeared only at the far end of the tank. From this original and simple experiment he concluded that the sun’s rays were broken by invisible particles into the blue uppermost strata of the sky, and the red/orange of sunsets resulted from the lower position and greater distance of the sun from earth. His conclusion was therefore correct, but it was later shown that individual molecules in the air, not dust particles, caused the scattering of light.

Tyndall’s discoveries of medical significance began in about 1875 when he discovered how to obtain air without particles, which he called “motes.” He built a wooden box with glass windows. Before closing the “Tyndall’s germ box” (Fig 2), he coated the walls and floor with glycerine. He was seeking motes of bacterial microbes with his microscope. After a few days the air was entirely free of particles when he shone strong light through the glass. The particles had stuck to the walls or sticky floor rendering it “optically pure.”

Investigating the “putrefaction and infection of the floating-matter of the air,” he used boiled urine as a culture medium with strict controls (“protected tubes”) from which air was excluded in his sealed germ box. On the 27th of September (1875), Tyndall reported that “for four months it has remained as transparent and of as rich a colour as the brightest Amontillado sherry. In those tubes exposed to air the liquid was turbid, laden with bacteria”:

I provided myself with a microscope having a magnifying power of 1200 diameters. Under its scrutiny the turbidity of the liquid immediately resolved itself into swarms of Bacteria in active motion.

Tyndall extended these experiments. He sterilized beef, lamb, and hay broths by boiling, and compared what happened when he placed these various broths in the optically pure air, and in ordinary air. Those in optically pure air remained “sweet” after many months, while the ones in ordinary air became putrid after a few days. This demonstration of bacteria extended Louis Pasteur’s earlier demonstrations that the presence of microorganisms is a precondition for fermentation and decomposition. However, the next year (1876) some of his supposedly heat-sterilized broths rotted in the optically pure air. From this he deduced the presence of bacterial spores (endospores) in supposedly heat-sterilized broths since a spore could survive boiling. Tyndall found a way to eradicate the bacterial spores (Tyndallisation) b : the first effective way to destroy bacterial spores.

Tyndall’s continual scientific questioning was brilliant and original. His experiments were effected with elegant simplicity. His extensive investigations into putrefactive organisms conformed to Koch’s identification of bacterial infection in the same year, 1876, and explained theories of putrefaction thus opposing Pasteur’s critics. 4

Germ theory had started with Antoni van Leeuwenhoek’s identification of “animalcules” in 1677. It preceded Pasteur and Koch’s Germ Theory that invisible microbes caused infectious diseases. Louis Pasteur (1822-95) showed in 1863 that microorganisms caused fermentation of milk and grapes, and the putrefaction of meat. He therefore suggested human disease was caused by the multiplication of germs in the body, though bacteria had not yet been demonstrated. 5 Gerhard Armauer Hansen (1841-1912) discovered the first causative bacterium in leprosy, M. lepra , in 1873. 6, 7 Robert Koch (1843-1910) in 1876 proved that Bacillus anthracis was the cause of anthrax, and crucially, was transmissible. 8 He went on to identify the bacterial causes of tuberculosis (1882), and cholera (1883).

Tyndall in this way also attempted to traduce the prevailing notions of spontaneous generation , supporting Francesco Redi (1626-97), the Italian poet and physician. “Aristotelian abiogenesis,” or spontaneous generation, postulated that living organisms sometimes arise from non-living matter. The neurologist Charlton Bastian became notorious for these controversial views, in which he was opposed by no less than T.H. Huxley, Pasteur, and Tyndall. He consequently suffered much opprobrium. 9 But many scientists, such as Huxley, Darwin, and Haldane, in parallel vein, continued to suggest a “primordial archebiosis,” a not dissimilar hypothesis.

John Tyndall’s early struggles

Life for the aspiring scientist was not easy. As a child, Tyndall with his family moved to Nurney, and then to Castlebellingham, where he received his schooling, returning to Leighlinbridge in 1836, where he became a teacher at the school in Ballinabranna. He worked with the Irish Ordinance Survey in Carlow in 1839 for nine shillings (45 p.) a week, then joined the survey’s office in Cork as a mapper until 1842. But he read widely in his leisure time and wrote articles for the local newspaper.

He then worked as a railway engineer, but started to keep daily diaries of his reading, personal beliefs, and ideas. A thoughtful, serious youngster he especially hated sham and mistrusted political, social, and scientific reforms.

His scientific endeavors began in August 1847 when he joined George Edmondson, the principal of Queenwood School, Stockbridge, Hampshire, as teacher of mathematics and surveying. Edward Frankland was lecturer in chemistry, and the two agreed to teach each other chemistry and mathematics. However, their careers failed to advance and in 1848 they sought instruction under Bunsen in the more scientific University of Marburg in Hesse, where despite living in poverty he studied for his PhD, obtained in 1850. 2

Tyndall began to investigate diamagnetism (substances that are repulsed from a magnetic pole) and the magneto-optic properties of crystals, which led to further publications in the Philosophical Magazine in 1850 and 1851. On a brief return to Britain in June 1850 he reported his investigations on diamagnetism at the British Association for the Advancement of Science meeting in Edinburgh, which though controversial was well received.

Experiments at The Royal Institution

Tyndall returned to Queenwood in 1851 as lecturer in mathematics and natural philosophy. On his way to the British Association meeting in Ipswich in July 1851 he met Thomas Huxley, and a warm, enduring friendship resulted. His talents were recognized by M. Faraday, W. R. Grove, Thomas Huxley, J. J. Sylvester, and John Phillips, who supported Tyndall’s election as Fellow of the Royal Society on 3 June 1852. He gave his first evening lecture at the Royal Institution on 6 July 1853 and in November of that year was appointed there as Professor of Natural Philosophy, 1853-1887. In 1867 he succeeded Faraday as superintendent of the Royal Institution directing the laboratory; he became Honorary Professor in 1887. He was devoted to Faraday, 2 writing his biographical Faraday as a Discoverer in 1868.

Greenhouse Gases

Climate change is not a new idea. It started when Tyndall established the idea of a “greenhouse gas” in the 1850s, when he showed that certain gases were transparent to visible light, but mostly opaque to the infrared. In 1859 he showed that water vapor and carbon dioxide absorb infrared radiation and could therefore affect the climate of the Earth. When his paper was published in 1861 in the Proceedings of the Royal Society, his press release explained that all past climate changes were now understood and future climate changes could be predicted from knowing the concentrations of these greenhouse gases. More than a century later these effects and their influence on the climate were established. 10 In the Earth’s atmosphere, these gases allow light to come in from the sun but trap heat. Tyndall understood this, commenting that without this natural greenhouse effect, the Earth would be as cold as the moon or Mars and inhospitable for life.

With a passion for mountaineering, 1 he climbed Snowdon and travelled with T. H. Huxley to the Alps, where he studied glacial movement, though J.D. Forbes disputed his theories. He climbed the Matterhorn and Mont Blanc in 1857 and Monte Rosa (4634m) the following year, in shirtsleeves, armed with half a flask of tea and a bacon sandwich.

He attended the “X-club” in 1864, a dining club of nine academically liberal scientists who supported theories of natural selection; they included biologist T. H. Huxley, chemist Edward Frankland, botanist Joseph Hooker, and the philosopher Herbert Spencer.

Promoting science to the public

Tyndall wrote many popular scientific texts and frequently engaged in polemical lectures. He published tutorials on heat, sound, and light that portrayed and explained experimental physics with new concepts to aid understanding:

“Written with a desire to interest intelligent persons who may not possess any special scientific culture.”

At the famous public schools Eton and Harrow, he tried to advance the teaching of science. To this end he published in 1870 the Essays on the Use and Limit of the Imagination in Science . His lectures were renowned for their charm and lucid language and for his exciting experimental demonstrations. He thus did much to popularize science.

Tyndall, like Darwin, had serious conflicts with religious authority. 4, 11 His role as a public communicator of science faced severe opposition. Notable was his presidential address to the 1874 meeting of the British Association at Belfast, espousing scientific naturalism – the view that things in nature are best explained without invoking theology. Seen as a grave threat to Christian doctrines he was harshly impugned by many, including Henry Wace, in an 1878 article in the Quarterly Review.

At the age of 55, Tyndall married Louisa Charlotte, daughter of Lord and Lady Hamilton of Sussex, in Westminster Abbey. The happy marriage bore them no children.

In 1886 Tyndall fell seriously ill. The following year he retired from the Royal Institution and withdrew to his house at Hindhead, near Haslemere. He often took chloral hydrate for his insomnia, and aged seventy-three he died in 1893 from an accidental overdose of this drug. He was buried at Haslemere. His wife Louisa devoted much of her long life to commemorating her husband and his works, eventually published by Eve and Creasey. 2

It is difficult to overestimate Tyndall’s passion for scientific truths. This drove his several elegant and wonderfully conceived experiments. He displayed remarkable stamina, an intense sense of duty, a love of poetry, and generosity to friends. But he was willing to contest opinions that he believed mistaken. In addition to his original papers on heat, glaciation, and physical sciences, Tyndall’s demonstrations of the particulate nature of air and bacteria constituted a vital element of the early studies of microbiology and its medical consequences. His ability to move from electromagnetism through thermodynamics and into bacteriology was one mark of his genius. 2 He was a champion of the scientific method, which he expounded so well in his public lectures that they attracted great crowds at the Royal Institution. His rational opinions, however, imperilled the traditional religious hegemony of his time.

He was a fine example of what in today’s flummery is clumsily called “blue sky thinking.”

License to practice surgery was marked when the Royal College of Surgeons finally separated barbers from surgeons in 1800. The 1858 Medical Act established the General Council of Medical Education and Registration (GMC). Although effectively a gentlemen’s club at the time, its purpose was: “Persons requiring medical aid should be enabled to distinguish qualified from unqualified practitioners.”
Food is boiled for about 15 to 20 minutes on three consecutive days. Any microorganisms not killed by the first day’s boiling session will germinate from the warmth and get released from their spore coatings, and then get killed in subsequent boiling.
Jackson R. The Ascent of John Tyndall: Victorian Scientist, Mountaineer, and Public Intellectual Oxford University Press, 2018.
Eve AS, Creasey, CH. Life and Work of John Tyndall. London: Macmillan. 1945.
‘Tyndall, John.’ Complete Dictionary of Scientific Biography. Encyclopedia.com. (September 30, 2018).
Brock WH, McMillan ND, Mollan RC. eds., John Tyndall: essays on a natural philosopher . Royal Dublin Society 1981.
Pasteur L. Recherches sur la putrefaction, Comptes Rendus de l’Académie des Sciences 1863;66:1189-1194.
Hansen A. Indberetning til det Norske medicinske Selskab i Christiania om en med Understøttelse af Selskabet foretagen reise for at anstille Undersøgelser angående Spedalskhedens årsager, tildels du førte sammen med forstander Hartwig. Norsk Mag Laegevidenskaben 1874;4 ( Suppl. 9 ): 1 – 88.
Pearce JMS. Hansen’s bacillus. Advances in Clinical Neuroscience and Rehabilitation 2018;17(4);16-18.
Koch R. Untersuchungen über Bakterien: V. Die Ätiologie der Milzbrand-Krankheit, begründet auf die Entwicklungsgeschichte des Bacillus anthracis. Cohns Beitrage zur Biologie der Pflanzen 1876;2, no. 2, 277–310.
Pearce JMS. Henry Charlton Bastian (1837-1915): Neglected Neurologist and Scientist. Eur Neurol 2010;63:73-8.
Tyndall John, Collections, The Royal Society. Ref No: EC/1852/13 https://collections.royalsociety.org/DServe.exedsqIni=Dserve.ini&dsqApp=Archive&dsqDb=Catalog&dsqSearch=RefNo==%27EC%2F1852%2F13%27&dsqCmd=Show.tcl.
DeYoung UA. Vision of Modern Science: John Tyndall and the Role of the Scientist in Victorian Cultur e. Springer, 2011.

JMS PEARCE, (MD, FRCP), is emeritus consultant neurologist in the Department of Neurology at the Hull Royal Infirmary, England.

Winter 2019

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Today, we cast a new light on disease. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

M ary Shelley spent the summer of 1816 in Switzerland. First she read Erasmus Darwin's ideas about the spontaneous generation of life in rotting food. Then she wrote her own story about generating life. She wrote the novel Frankenstein .

Sixty years later, another English visitor summered over in the Swiss Alps. He was the physicist John Tyndall. Like Shelley, he'd also thought about the spontaneous generation of life. In spring, a nearby lake was clean and lifeless. By summer's end it teemed with life. If you weren't careful, he said, you could think that life arose spontaneously in the sterile melted snow.

Today, we know Tyndall for his work with heat, light, and sound. We forget his work on micro-organisms and airborne disease. Yet it stands right along with Pasteur's and Lister's.

He'd begun in the 1860s when he was studying light. He wanted to make air dust-free. So he created the Tyndall Box. He coated the walls inside a sealed box with glycerin.

After 3 days, all the particulates in the air stuck to the walls and left the air in the box clean as a whistle. Tyndall had made the air optically pure. He showed that beams of light are invisible when they enter a window and pass through clean air.

By now doctors knew that dirt and dust caused disease. They also suspected that germs might be major agents of disease. Tyndall put those ideas together. He saw that by cleaning the air he'd removed the vehicle that carries micro-organisms.

To make his point, he exposed test tubes of urine to the clean air in a Tyndall box. Bacterial life grew in the test tubes under normal air. They stayed sterile in the box. So he repeated the experiment with meat, fish, and vegetables. Same story. None of them putrefied in clean air, either.

He made his work public in 1870. Then the fun began. Biologists attacked him. One of them, a believer in spontaneous generation, scalded him for "quitting his own metier." He told Tyndall that the germ theory of disease was the business only of biologists and physicians.

We hear a lot of that today. Don't talk about poetry if you're a historian. You can't understand medicine unless you're an M.D. Tyndall shot back: If that were true, then the chemist Pasteur shouldn't be allowed to study germs.

Tyndall began by studying light. When he was done, he'd pinned down the origin of disease. He brought alien knowledge to biology. He changed biology when he took it into that clever box -- and cast the clean invisible light of his physics upon it.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Tyndall, J., Essays on the Floating-Matter of the Air . (Reprinted from the New York Edition of 1882, R.N. Doetsch, ed.) New York: Johnson Reprint Corp., 1966.

Tyndall is a fascinating and underrated scientist. For more on the man, see Episodes No. 192 , 531 , and 624 .