Part I: The story you might have heard before
Experiments are at the core of science. Scientists like elegant experiments, ones that conclusively prove a point in a minimum of time with a minimum of apparatus. It helps if it’s a little dramatic too.
Microbiologists enjoy telling a story about Helicobacter pylori, now recognized as the main cause of peptic ulcers. Ulcers had been studied since the 16th century, but until the 1980s, it was thought that ulcers were mostly caused by stress and a bad diet. A series of discoveries led some scientists to suspect that ulcers were in fact caused bacteria. Two scientists, Barry Marshall and Robin Warren, were able to culture H. pylori, and they contended that the bacteria was the principal cause of ulcers.
In 1984, Marshall drank a culture of H. pylori. In a few days, he developed gastritis that was cleared by taking antibiotics. This “elegant” experiment didn’t show that H. pylori caused ulcers, but they add credence to the idea that the microbe played a role in gastritis, ulcers, and stomach cancer.
Marshall’s experiment took place in the context of conflicting evidence about the role of bacteria in peptic ulcers. Some experiments had failed to demonstrate the antibiotics treat ulcers; others had failed to show that H. pylori is infective. The story is often told in a neat way (man drinks broth, man proves point), but I think that story only arises in retrospect. If things had gone differently (e.g., if he hadn’t gotten sick), then Marshall would have seemed kooky for a lot longer.
Part II: The story you probably haven’t
Epidemiology textbooks often point to 1854 as a critical moment in the origin of epidemiology. In that year, John Snow, a London doctor, made a map showing that cases of cholera in London clustered around a single water pump on Broad Street. The easy-to-digest story says that Snow told the city that the pump was the cause of the outbreak, that the city removed the handle from the pump, and that the outbreak then declined. (Snow himself was unsure of whether the outbreak was in decline before the handle was removed.) Not only did Snow help end the outbreak, he also help prove the contagion (i.e., transmissive) theory of disease. For thousands of years, Western medical tradition had asserted that diseases were due to a combination of imbalances in the humors and some miasma or “bad air”.
In his Plagues and Peoples, W. H. McNeill points out that the story is more complicated. He says that the microscope was only beginning to be used to identify disease-causing microorganisms in the 1880s, and it was only in 1883 that Robert Koch had isolated the bacteria responsible for cholera, Vibrio cholerae. Even after Koch’s discovery, there was controversy:
Since many learned and respected doctors had committed themselves to the miasmatic theory as explanation of epidemic, it is not surprising to find that Koch’s explanation for the cause of cholera met stout resistance among experts. As late as 1892, a famous German doctor drank a beaker full of cholera bacilli to prove the falsity of the germ theory—and gleefully informed his professional rivals that he had experienced no ill effects. (Longmate, King Cholera, p. 229) No doubt he was lucky; but his act dramatized the uncertainties that still surround the question of what factors affect transmission of cholera infections.
Today this unnamed doctor seems laughably misguided. Drinking cholera? I think this, again, is only possible in hindsight. Both Marshall and the cholera-drinker appear to have been driven by frustration, and they hoped for a single, risky, elegant demonstration that they were right. Maybe the lesson is that science is driven by a preponderance of multiple lines of evidence, while popular stories about science are driven by single, easy-to-digest events (e.g., Newton is hit by an apple).