In 1822, a stomach wound was most often a death sentence. Alexis St. Martin didn’t die–but his life was irrevocably changed.

On this day, 195 years ago, St. Martin was accidentally shot at Fort Mackinac, Michigan. And he never fully healed. The bizarre window into his digestive system created the circumstances for a strangely intimate relationship between Martin, a Canadian fur trapper, and the fort doctor, William Beaumont. But that curious bond resulted in some important early insights into how human digestion works.

The French Canadian man was extremely close to the gun when it went off, Esther Inglis-Arkell reports for io9. The bullet traveled through St. Martin's side, tearing a hole right through the wall of his stomach. “When he ate, food actually fell out of him,” she writes. He was kept alive by ‘nutritious enemas.’ And as the edges of his stomach healed, they adhered to the edges of his belly skin, she reports. The result: a permanent window into his stomach.

As Frank Straus writes for the Mackinac Island Town Crier, St. Martin's continuing disability cost him his job at the American Fur Company—where he worked under indentured servitude. Losing his job meant he needed community support, but St. Martin wasn't considered a Mackinac Island local, writes Straus. The island’s leaders suggested sending him back to Quebec.

Beaumont didn’t think St. Martin would survive the venture—and he saw a scientific opportunity. So he took St. Martin on as a house servant, and, in the evening, a guinea pig.

According to Straus, a renewal contract that St. Martin (who couldn’t read) signed in 1832 said that he would “submit to...such Physiological or Medical experiments as the said William shall direct or cause to be made on or in the stomach of him, the said Alexis...and will obey...the exhibiting and showing of his said Stomach.”

The two embarked on a long and strange relationship; “medicine’s oddest couple,” according to author Mary Roach.

Beaumont watched as St. Martin digested different kinds of food. He sampled the man’s stomach acid, conducting experiments with vials of the stuff. At one point, he actually licked St. Martin’s empty stomach, discovering that it didn’t have an acid taste until it was actively working to digest food.

Whether or not this relationship was ethically sound, however, has long been debated. Beaumont promised to eventually sew the man's stomach up. But he never did. How hard did he work to close St. Martin’s hole? Even though the "gastric fistula" (as it's medically called) provided an unprecedented scientific opportunity, it also affected the trapper's quality of life. Was the doctor actually acting, as Beaumont wrote, “from mere motives of charity”? Could he not have sent the man home safely after his condition stabilized?

This state of affairs continued for years, writes Inglis-Arkell. St. Martin got married and had six children. According to Beaumont, he even returned to Canada in 1831 for almost a year before returning for another round of experiments. But eventually, he asked for too much money from Beaumont and the duo parted ways.

“He did tour medical facilities,” Inglis-Arkell writes, “but eventually all but disappeared into the back woods.” Although he was hounded by medical doctors who wanted to peek into his stomach, she writes, he didn't give in again.