On a wintry day in the mid-1930s, a concerned farmer appeared at the door of a lab at UW-Madison.

In his hand was a can of blood, taken from one of his cows. Many of the cows on his farm had mysteriously died after eating sweet clover hay that had mold on it. So the farmer asked UW-Madison biochemist Karl Paul Link to solve the mystery.

Link found that a chemical reaction occurred when a fungus in the mold met with a substance in hay called coumarin. This discovery would eventually lead to breakthrough developments in medical treatments and pharmaceuticals. Watch the video from NPR below or read the full story on NPR’s website to learn more.