American Army surgeon William Beaumont made some of the first in vivo (in the living body) observations of the physiology of the human digestive system.

Beaumont, Connecticut-born and the son of a farmer, worked briefly as a school teacher, then studied medicine at St. Albans, Vermont. After an apprenticeship, Beaumont received a license to practice medicine in time to serve as an assistant army surgeon during the War of 1812. Although he left the army in 1815 to start a medical practice in Plattsburgh, New York, he returned in 1820 and remained an Army surgeon, serving at various posts, until 1839.

It was at one of those army posts, Fort Mackinac in northern Michigan, that Beaumont met the patient that was to make both of them famous. The patient was a 19-year-old French Canadian trapper, Alexis St. Martin who, on June 6, 1822, was accidentally shot while visiting the Mackinac branch of the American...