9781848931824 Steven Shapin reviews Ian Miller's A Modern History of the Stomach: Gastric Illness, Medicine and British Society, 1800-1950, in LRB:

Alexis St Martin was one of the 19th century’s most important scientific guinea pigs. In 1822, the illiterate young French-Canadian was working as a ‘voyageur’ for John Jacob Astor’s fur-trading company in northern Michigan. He was hanging out with a bunch of rowdies in the company store when a shotgun accidentally went off and he was hit below his left nipple. The injury was serious and likely to be fatal – his half-digested breakfast was pouring out of the wound from his perforated stomach, along with bits of the stomach itself – but a US army surgeon called William Beaumont was nevertheless sent for. Beaumont was pessimistic, but he cleaned the wound as best he could and was amazed the next day to find his patient still alive. It was touch and go for almost a year: St Martin survived, though with a gastric fistula about two and a half inches in circumference. It was now possible for Beaumont to peer into St Martin’s stomach, to insert his forefinger into it, to introduce muslin bags containing bits of food and to retrieve them whenever he wanted. Human digestion had become visible.

Beaumont took over St Martin’s care when charity support ran out, and over the next ten years the patient lived intermittently with the doctor, as both his domestic servant and a contractually paid experimental object. St Martin’s fistula was soon to become one of the modern world’s most celebrated peepshows. The experiments were conducted at intervals over the eight years from 1825 and a remarkable contract survives which established a legal basis for scientific access to St Martin’s stomach:

Alexis will at all times … submit to assist and promote by all means in his power such philosophical or medical experiments as the said William shall direct or cause to be made on or in the stomach of him, the said Alexis, either through and by means of the aperture or opening thereto in the side of him, the said Alexis, or otherwise, and will obey, suffer and comply with all reasonable and proper orders of or experiments of the said William in relation thereto, and in relation to the exhibiting and showing of his said stomach and the powers and properties thereof and of the appurtenances, and powers, properties, situation and state of the contents thereof.

In return for letting Beaumont in and out of his stomach, St Martin was to get board, lodging and about $150 a year. But by 1833 he’d had enough: he went back to his old life as a voyageur, and, amazingly, lived well into his seventies.