We didn't always know everything about nutrition and digestion. Scientists and doctors knew that food didn't look the same going in and coming out—we don't need fancy degrees on our wall to figure that out. They knew some mysterious process was happening, but they didn't have a way of studying it since everything was occurring inside our bodies.
Everything changed one fateful day in 1822 at Mackinaw Island, Michigan. A poor fur trader named Alexis St. Martin was accidentally shot in the stomach from just a few feet away. He managed to survive, but by the time doctors arrived, he had a hole in his gut and his breakfast was hanging out for everyone to see.
One of his doctors, Dr. William Beaumont, who had only completed one year of medical training, kept a close eye on his patient. With a gaping hole in his guts, anything that St. Martin ate popped right out. Since anal injections of food weren't (and still aren't) incredibly satisfying, Dr. Beaumont put a bandage over the hole to keep food inside.
The hole never healed or properly sealed. It ended up creating a gastric fistula, or a permanent opening. Normally, an open hole in your belly isn't really thought of as a great thing, but for Beaumont, it offered a window into the world of digestion. The doctor was so curious about digestion that he would dangle pieces of food tied to string into St. Martin's stomach hole, remove it, and then analyze how the food had been digested. He would spoon an egg into the fistula, and remove it after a certain amount of time to see how long it takes for a hardboiled egg or one that's cooked sunny-side-up to be digested.
Dr. Beaumont ended up paying St. Martin to stay in his house so he could constantly keep experimenting on his stomach hole. Needless to say, they didn't become BFFs. This type of research continued for ten years. Gross.
What did we learn from these gruesomely interesting scientific experiments? Prior to 1822, and before Beaumont published his study, scientists thought stomach digestion was either mechanical or chemical. Either the stomach ground food into tiny pieces or it had enzymes that broke food down. Beaumont's experiments settled the debate, and he concluded that the stomach had gastric juices and HCl to digest food. Thank goodness for gastric fistulas.