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.

This story appears in the August 2020 issue of National Geographic magazine.

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

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.

Pringle estimated that the British army lost a quarter of its strength to sickness alone during the 1743 campaign. He set out to change that, working through the military command to turn his insights into orders. In setting up campsites, quartermasters were told to avoid damp, poorly ventilated areas and to dig proper latrines in advance.

Hospitals were the soldiers’ other great enemy. Pringle noticed that men treated in camp rather than in the general hospital typically avoided hospital fever, as typhus was called. Keeping them in camp became standard, where possible. In hospitals, patient space was to be clean, well ventilated, and a minimum of 36 square feet for each man. Bed linens were to be changed frequently. These reforms quickly paid off. Mortality at the general hospital fell by more than half, from 21.4 percent in 1743 to 9.8 percent over the next two years of fighting.

In 1752 Pringle published his book Observations on the Diseases of the Army. It went through multiple editions over the next two decades, spreading his sanitary gospel through the British military. In translation, it also reached French, German, and Italian armed forces. Recognizing filth theory’s success in cleaning up the military, pioneering public health advocates soon began a new war on filth: in the rising cities of the industrial revolution. Read more about how devastating pandemics change us.

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