William Beaumont, (born Nov. 21, 1785, Lebanon, Conn., U.S.—died April 25, 1853, St. Louis, Mo.), U.S. army surgeon, the first person to observe and study human digestion as it occurs in the stomach.

On June 6, 1822, while serving at Fort Mackinac (now in Michigan), Beaumont was summoned to Michilimackinac to treat Alexis St. Martin, a 19-year-old French-Canadian trapper, who had been wounded at close range by a shotgun blast. The shot had removed a portion of the abdominal wall and left a perforation in the anterior wall of the stomach. During the year it took for the wound to heal, the aperture in the abdominal wall never sealed but was held closed by the inversion of tissue surrounding it. As a result, a gastric fistula, or passage, remained. When it was depressed with the finger, Beaumont could view the activities occurring within St. Martin’s stomach.

Three years after the near-fatal accident Beaumont began physiological studies of St. Martin’s stomach. He believed that the process of digestion was essentially a chemical process carried out by chemicals in the stomach. Determined to prove this hypothesis, he collected samples of gastric juice and sent them for analysis to several chemists, who established the presence of free hydrochloric acid in the juice. Beaumont also reported on the effects of different foods on the stomach, finding that vegetables were less digestible than other foods, that milk coagulated prior to the onset of digestion, and that cold gastric juice had no effect upon food. In 1833 he published Experiments and Observations on the Gastric Juice and the Physiology of Digestion.

Beaumont’s experiments threw new light upon the nature of gastric juice and the digestive process in general, and established alcohol as a cause of gastritis (inflammation of the stomach’s mucous membrane).