In the 1920s, something was happening to the cows. They kept bleeding, even though cattle are pretty good at stopping bleeding on their own. When you castrate a bull, for example, he tends to get over it quite quickly, no matter how painful the process sounds. These 1920s bulls, though, bled out through where their balls had been. So did cows who just nicked their horns a bit.

Farmers narrowed the problem down to the kind of rotting feed the cattle were eating, and so they dubbed the problem “sweet clover disease.” Scientists looked at this feed to discover what was wrong, and in the process, they discovered the disease was totally reversible. Just give the cows Vitamin K, and they’d start clotting fine—the mystery poison worked by deactivating the vitamin, but an extra dose of the vitamin shifted the balance again. That fixed things for the farms, then the scientists kept their work going, investigating the chemical that makes blood all runny.

After a whole lot of experiments, some with bunnies, they isolated the chemical. They called it dicoumarol, then they made a variant called warfarin. They now had a drug to make animals bleed to death, which is more useful than it sounds: They used it to make rat poison. That’s how this type of rat poison works; the poison doesn’t kill the rat directly, but it keeps their blood from clotting, so they either die by internal bleeding or inevitably scrape themselves on something and bleed out. 

Then came April 5, 1951. An army recruit in Philadelphia ate a bunch of warfarin, attempting suicide. This put his health at some risk but did not kill him right it off, instead giving him enough time to realize he didn’t want to die. He checked himself into the hospital, which treated him easily with that useful Vitamin K and some blood transfusions. This also, for the first time, gave medical personnel a really close look at what warfarin does to human blood. It thins human blood ... which is a desirable effect, when you manage it properly. And that is why, today, warfarin is an anticoagulant, useful for keeping dangerous clots from choking patients’ hearts and brains. 

We’d like to leave you with the final lines from a 1959 paper by the discoverer of warfarin, Karl Paul Link, documenting this history. He credits those who developed warfarin for medical use (the italics are present in the original text). “I think the secret of their success is 3-pronged: they never ceased to wonder, they kept on trying, and they were on a project directed toward doing mankind some good instead of trying to destroy it.”

We have no idea what he’s passive-aggressively referring to at the end there. He doesn’t mention it at all anywhere else in the paper. 

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For more medical discoveries, check out:

Gastroenterology Is Created by Shoving Random Things into a Man's Stomach Hole

Francis Crick Discovers DNA Thanks to LSD

The Runny Nose That Was Actually Leaking Brain Fluid

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