Cobra Effect · Body and medicine
Germs do not come from nowhere
How a swan-neck flask and a country doctor proved that germs cause disease.
7 cards, read aloud in 3:13, with a test and sources.
For centuries, many people believed living things could spring from lifeless matter.
Maggots appeared on rotting meat, and mould grew on old bread. It seemed that life simply arose, all by itself, from things that were decaying. This idea was called spontaneous generation. Even after microscopes revealed tiny living things, many assumed they formed on their own.
Around 1859, Louis Pasteur tested the idea with a flask shaped like a swan’s neck.
He boiled broth in a flask whose long neck curved down and then up again. Air could still get in, but dust and microbes from the air settled in the bend of the neck. The boiled broth stayed clear, with nothing growing in it. Nothing had arisen on its own.
When the neck of the flask was broken off, the broth went cloudy.
Once dust and microbes from the air could fall straight in, they began to multiply. Before long the broth was teeming with microbes. Life in the broth came from microbes carried in, not from the broth itself. In 1862 the French Academy of Sciences gave Pasteur a prize for this work.
In Germany, Robert Koch linked a particular germ to a particular disease.
Koch was a country doctor who studied anthrax, a disease that killed farm animals. He grew the anthrax bacteria outside the body, and watched them form tough spores. The spores could survive in soil for years, which explained why the disease came back to fields left empty a long time. He presented his findings in 1876.
In 1882, Koch found the germ that causes tuberculosis.
Tuberculosis was one of the leading causes of death in Europe at the time. Koch found the bacterium in diseased tissue, grew it in the laboratory, and gave the disease to healthy animals with it. He announced his discovery in Berlin in March 1882. The day of his announcement is now marked every year as World Tuberculosis Day.
Koch’s approach became a set of tests for proving that a germ causes a disease.
The germ should be found in those who have the disease. It should be grown on its own, in a pure culture. Given to a healthy animal, it should cause the same disease. And it should be found again in the newly sick animal. These tests became known as Koch’s postulates.
So when something seems to appear from nowhere, ask where it came from.
Once germs were understood, surgeons began to clean their hands and instruments, and deaths from infection fell. Boiling, filtering and heating food and water became ways to kill germs. Koch was awarded the Nobel Prize in 1905. Things that seem to come from nothing usually came from somewhere nobody was looking.
Sources
- Louis Pasteur: spontaneous generation, Britannica. How the swan-neck flask experiments settled the question.
- Robert Koch: biographical, NobelPrize.org. Koch’s work on anthrax, tuberculosis and cholera.
- Koch’s postulates, Wikipedia. The four tests for linking a germ to a disease, and where they fall short.
Nearby ideas
- From a milkmaid’s hand to the end of smallpox. How a country saying about milkmaids led to the first vaccine and the end of smallpox.
- The doctor who drank the germ. How a doctor drank a germ to prove that bacteria, not stress, cause most ulcers.
- The pump that spread cholera. How a map of deaths around one pump showed that cholera spreads through water.
- The blood goes round. How a simple sum showed that the same blood goes round and round the body.
- Penicillin needed more than luck. How a mouldy dish became a medicine only after a team made it work.
- The extract that saved a boy. How a quarrelling team in Toronto turned a deadly disease into one people could live with.