Louis Pasteur’s 19th-century Medical Discoveries Are Still Saving Lives

Beer and wine were critical to the economy of France and Italy in the 1800s. It was not uncommon during Pasteur’s life for products to spoil and become bitter or dangerous to drink. At the time, the scientific notion of “spontaneous generation” held that life can arise from nonliving matter, which was believed to be the culprit behind wine spoiling.

While many scientists tried to disprove the theory of spontaneous generation, in 1745, English biologist John Turberville Needham believed he had created the perfect experiment favoring spontaneous generation. Most scientists believed that heat killed life, so Needham created an experiment to show that microorganisms could grow on food, even after boiling. After boiling chicken broth, he placed it in a flask, heated it, then sealed it and waited, not realizing that air could make its way back into the flask before sealing. After some time, microorganisms grew and Needham claimed victory.

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However, his experiment had two major flaws. For one, the boiling time was not sufficient to kill all microbes. And importantly, his flasks allowed air to flow back in, which enabled microbial contamination.

To settle the scientific battle, the French Academy of Sciences sponsored a contest for the best experiment to prove or disprove spontaneous generation. Pasteur’s response to the contest was a series of experiments, including a prize-winning 1861 essay.

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Pasteur deemed one of these experiments as “unassailable and decisive” because, unlike Needham, after he sterilized his cultures, he kept them free from contamination. By using his now famous swan-necked flasks, which had a long S-shaped neck, he allowed air to flow in while at the same time preventing falling particles from reaching the broth during heating. As a result, the flask remained free of growth for an extended period. This showed that if air was not allowed directly into his boiled infusions, then no “living microorganisms would appear, even after months of observation.” However, importantly, if dust was introduced, living microbes appeared.

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Through that process, Pasteur not only refuted the theory of spontaneous generation, but he also demonstrated that microorganisms were everywhere. When he showed that food and wine spoiled because of contamination from invisible bacteria rather than from spontaneous generation, the modern germ theory of disease was born.

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