Pasteur, Koch and the Germ Theory Revolution
The Wrong Theory That Almost Made Sense
For most of the 19th century educated British people believed disease came from miasma — bad air rising from rotting waste, sewage and stagnant water. Cholera in Soho? Bad air from the cesspits. Childbed fever in maternity wards? Bad air from the linen. Hospital wounds going septic? Bad air from open windows. Miasma theory was wrong, but it was coherent: it predicted that clean smells meant safe places, dirty smells meant dangerous ones. It even produced useful action — hospital ventilation, street cleaning, lime in graveyards. The problem was that the actual cause of disease was invisible, and miasma blocked the search for it.
In 1861 Louis Pasteur published his germ theory, proving that microscopic organisms (germs) caused decay and disease. He had been investigating fermentation for the French wine and brewing industries; the medical implications followed.
Pasteur and the Germ Theory of Disease
Louis Pasteur was a French chemist, not a doctor. The French wine and beer industries hired him in the 1850s to find out why their drinks were going bad; the silk industry only called him in from 1865. By using a microscope and a series of swan-necked flask experiments, Pasteur showed that microbes carried in the air caused fermentation and decay. He published this as the Germ Theory of Disease in 1861. By the 1880s he had extended the principle into a vaccine programme: chicken cholera (1879, by chance — an old culture left over a holiday weekend turned out to immunise rather than infect), anthrax (1881, in a famous public demonstration where vaccinated sheep survived and unvaccinated ones died) and rabies (1885, on a 9-year-old boy bitten by a rabid dog).
Koch and the Microbe Hunters
Pasteur proved germs caused disease in general. Robert Koch, a German country doctor, took the next step: identifying which germ caused which disease. Working alone in a converted darkroom and later in Berlin, Koch developed the techniques that made modern microbiology possible. He stained bacteria so they could be seen under a microscope. He grew them on agar jelly so colonies could be isolated. He photographed them so others could see what he saw. In 1876 he identified the anthrax bacterium. In 1882 he found the bacterium that causes tuberculosis — then the biggest killer in Britain. In 1883 he identified cholera. Koch was the first to fulfil the ‘one germ, one disease’ rule that became the basis of modern medicine.
Pasteur was French; Koch was German. The two countries had fought a war (Franco-Prussian, 1870-71) and the rivalry continued in their laboratories. When Koch identified TB in 1882, Pasteur responded with the rabies vaccine in 1885. When Pasteur produced anthrax vaccination in 1881, Koch attacked his methods publicly. National pride drove output: governments funded laboratories partly to outcompete the other side.
For the AQA factor essay this is a lovely example of how science, communication and the role of the individual interact. Without rivalry, the pace of discovery would have been slower; without good communication (scientific journals, photographs of bacteria), the results would not have spread.
Ehrlich and the ‘Magic Bullet’
Paul Ehrlich, a German researcher trained under Koch, took germ theory in a new direction. If specific bacteria caused specific diseases, perhaps specific chemicals could destroy specific bacteria without harming the patient. Ehrlich called this idea a magic bullet. After testing 605 compounds, the 606th — a compound of arsenic now called Salvarsan — cured syphilis. He published this in 1909. It was the first chemical cure for an infectious disease. The next leap came in 1932 when the German company Bayer introduced Prontosil, a sulphonamide drug effective against streptococcal infection. The age of chemotherapy had begun — though large-scale antibiotics would have to wait for penicillin in the 1940s.
Why Britain Lagged
Pasteur published in 1861. Lister applied germ theory to surgery in Britain in 1867. By the 1880s, Koch had identified specific bacteria. Yet many British doctors and public health officials clung to miasma well into the 1880s.
Training: medical schools had taught miasma for decades; doctors trained before 1860 saw no compelling reason to switch frameworks late in their careers. Visibility: nobody could see germs without a microscope, and decent microscopes were expensive and required expert use. Communication: French research took time to translate into English, and British scientific culture was suspicious of Continental theory after decades of intermittent war with France. The shift was generational — older doctors retired, younger doctors trained in the new framework, and miasma quietly disappeared from the textbooks by the early 1900s.
Robert Koch identified the bacteria causing anthrax (1876), tuberculosis (1882) and cholera (1883). His staining and culture techniques made systematic bacteriology possible. By 1900 the ‘one germ, one disease’ rule was the basis of modern medical thinking.
Everyday Medicine in the Age of Germ Theory
For ordinary people in Britain, germ theory’s practical effects took time to arrive. Doctors continued to prescribe traditional remedies — cod liver oil, beef tea, mustard plasters — alongside new advice on hygiene. Hospitals began to insist on hand-washing, instrument sterilisation and clean wards by the 1890s. Patent remedies still flooded the market: Beecham’s Pills, Carter’s Little Liver Pills, Bovril marketed as a tonic. The professional doctor was now scientifically grounded in a way that had been impossible in 1860, but the patient’s medicine cabinet still mixed old and new.
Linking to the Factor Essay
Germ theory is the cleanest example in the unit of science and technology as the dominant factor — without microscopes, staining and the new theoretical framework, none of this happens. But the lesson also shows the other factors at work. Communication: Pasteur and Koch published in scientific journals that crossed borders rapidly. The role of the individual: Pasteur, Koch and Ehrlich made discoveries that depended on personal genius and persistence. Government: French and German states funded laboratories; British government was slower. Chance: the 1879 chicken-cholera vaccine came from a forgotten flask. A factor-essay question naming ‘science and technology’ can be answered using this lesson alone, but the strongest answers reach across periods to compare the role of science here with its role in earlier eras (Vesalius, Harvey) where science was necessary but not sufficient on its own.