Did a 1930s Wisconsin farmer not realize he helped discover one of the world’s most significant medical breakthroughs?

With a new historical landmark designation and a forthcoming book by Doug Moe, warfarin's origin story is finally being told.
Sepia toned portrait of Dr. Karl Paul Link in a white hat
Courtesy of Tom Link.
Warfarin was discovered and developed in Dr. Karl Paul Link's University of Wisconsin–Madison lab.

On Oct. 12, a dedication ceremony was held on the University of Wisconsin–Madison campus to celebrate a revolutionary discovery that both prolonged human lives and killed rats.

The American Chemical Society, or ACS, bestowed the National Historic Chemical Landmark designation on warfarin, the generic name for a prescription blood thinner that, in a slightly different form, proved to be an enormously effective rodenticide. The ACS established the awards in 1992 to recognize seminal events in the history of chemistry. An ACS board member, Dr. Lisa Balbes, was among several speakers at the dedication ceremony for warfarin, which was first marketed in the late 1940s and early ’50s.

As it happened, I was invited to say a few words as well, by one of the event’s organizers, Dr. Kevin Walters, public affairs analyst and historian for the Wisconsin Alumni Research Foundation, or WARF. Walters knew — my wife, Jeanan, is his colleague at WARF — that I have been researching and writing a biography of Dr. Karl Paul Link, the colorful UW–Madison biochemist in whose laboratory warfarin and its prequels were discovered.

I began my research several years ago at the behest of Karl’s son, Tom Link, who knew the magnitude of his father’s achievement. (Tom’s mother, Elizabeth “Lisa” Link, was also well known in Madison as an activist with the Women’s International League for Peace and Freedom.)

My book was sidetracked when the pandemic closed the library that houses Karl Paul Link’s considerable archive, but the finish line is now in sight.

I had, in any case, written about Link and warfarin earlier in newspaper columns. One of the most intriguing came in 2003 around the 50th anniversary of the death of Soviet dictator Joseph Stalin. I interviewed a Yale professor, Joseph Brent, who had coauthored a new book called “Stalin’s Last Crime” in which a theory was advanced that Stalin’s generals had fatally poisoned him with warfarin.

“Wouldn’t it be interesting,” Brent said, “if one of the biggest rats in history was killed by rat poison?”

There is no definitive conclusion as to Stalin’s cause of death, but a few days after that column appeared I received a warm and humorous letter from a reader in Arizona who said he’d worked as a “mail clerk and gofer” at WARF in the 1940s.

“One of my jobs,” he wrote, “was to buy a case of Budweiser in cans and put it in the refrigerator in the Biochem lab for Dr. Karl Paul Link every Friday afternoon. While I was helping him, he invented warfarin. [Many] years later, in 1997, I developed a blood clot in my leg. The Coumadin [the trade name for warfarin] they gave me dissolved the clot before it reached my lung. I helped Dr. Link and he saved my life.”

Of course, Link didn’t “invent” warfarin, but he led the team that across many years developed it. There is much more to say about that — a whole book! — but for now I’ll share something I related at the Oct. 12 warfarin landmark dedication about how Link first became interested in anticoagulants.

Link told the story himself, most famously during a 1958 address to the New York Academy of Medicine. It was a bitter cold Saturday in February 1933 and Link was in the Biochemistry building, along with a graduate student from Germany named Schoeffel. According to Link, a young farmer from St. Croix County — some 190 miles away — appeared “by chance” at Biochemistry after finding the state veterinarian’s office closed.

The farmer, Ed Carlson, was desperate. His cows were dying, bleeding out after skin punctures or through the nose. Their blood simply would not clot.

Link had recently become familiar with an animal malady called sweet clover disease. Cattle that ate spoiled — wet and moldy — sweet clover were susceptible to massive hemorrhaging.

Carlson’s appearance in Madison — the farmer had with him a dead heifer, a can of cow’s blood and abundant spoiled sweet clover — had a profound effect on Link, who could only counsel Carlson not to feed cattle the spoiled sweet clover. The farmer left, dejected.

Link — spurred on by Schoeffel, his assistant, who called Carlson’s out-of-the-blue visit “destiny” — began, with the students in his lab, to try to determine what it was in the spoiled sweet clover that kept blood from clotting.

They did. It took years. The cast of researchers evolved, though Link remained the leader. Various compounds were patented. Finally, warfarin (the rodenticide) and warfarin sodium (the human anticoagulant) emerged as the game-changers deserving of national landmark status.

Over time, and especially after Link’s death in 1978, some of his colleagues expressed doubt about the farmer Carlson story. It was almost too good to be true, they said. The most uncharitable suggested they should stop repeating “a fable.”

In researching my book, and with the help of Dee Grimsrud, a distinguished Madison genealogist and historian, I was able to determine there was a farmer named Ed Carlson in St. Croix County in 1933, age 21, whose father had also farmed, as Link noted in a later interview.

I recently had a chance to interview Carlson’s son, an emeritus professor at UW–Stevens Point, who said his father never said anything about Link or warfarin.

A plaque honoring the national landmark status of warfarin will soon be installed at the Biochemistry complex on campus. Interesting that the farmer, whose long drive to Madison in 1933 sparked one of the 20th century’s most significant medical breakthroughs, may not have realized he did.

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