We’ve known for a hundred years that the brain can control important aspects of the stomach. In 1822, a fellow named Alexis St. Martin was shot in the stomach and was treated by Dr. William Beaumont, who didn’t expect his patient to live. Against the odds, St. Martin survived, but his body formed a fistula, or a hole, from his stomach to his side. It was pretty much gross and had to be bandaged up to keep stomach acids from squirting out, but Dr. Beaumont was delighted. It gave him an unprecedented living laboratory for studying human digestion.

Seizing the opportunity, Dr. Beaumont took St. Martin on as a servant and semi-willing guinea pig. The doctor extracted  stomach juices through the fistula and had them analyzed. He tied string around different foods, dipping them into the stomach of the amazingly  tolerant St. Martin and then retracting them over time to monitor the digestion process. This catch-and-release strategy illuminated many new details of digestion.

St. Martin, on the other hand, was not always thrilled with these fishing expeditions and sometimes complained. During a particularly acrimonious examination,  Dr. Beaumont found significant changes in the acidity of St. Martin’s stomach juices. Beaumont had discovered something completely unexpected: emotions could directly affect the chemistry of the stomach.

This is not an atypical science story. Science advances when we get new tools, like microscopes and telescopes, that allow us to see things that are normally hidden. Alexis St. Martin’s fistula was just such a scope, providing one of the first windows into a living stomach, and making Alexis the true hero of this story.