His discovery about the dangers of filth saved countless lives

Appalled by conditions he saw in an army hospital, a British doctor in the 1740s made changes that improved hygiene on and off the battlefield.

In the aftermath of a victory over the French in 1743, about 1,500 British soldiers, uninjured but deathly ill, straggled into the army’s general hospital in a village on the outskirts of Frankfurt, Germany. Men lay two or more to a bed and packed together on the floor. Most of the sick had dysentery, and everything was inevitably covered with excrement, urine, blood, sweat, and vomit. Fleas and lice abounded. Dysentery soon gave way to typhus. Hundreds died.

John Pringle, an army physician on his first campaign, observed the dying in horror. The ideas he developed for preventing illness became one of the earliest expressions of filth theory. It held, in brief, that filthy conditions foster diseases and that sanitation helps prevent them.

Born in 1707, Pringle was the youngest son of minor Scottish aristocracy. He had earned respect lecturing at the University of Edinburgh in moral and natural philosophy, which mostly meant learning about the living world through experimentation, observation, and inductive reasoning. When the War of the Austrian Succession began, he won appointment as physician general to the entire British force, 16,000 men. He soon proved his worth.

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