Mackinac Island continued to be a locus of trade for the American Fur Company and was the site where Army doctor William Beaumont became Post surgeon in 1820 and began conducting his famous digestion experiments on 19-year-old Alexis St. Martin between 1822 and 1833. Mackinaw Island was also the site where Henry Schoolcraft located his US Indian Agent headquarters starting in 1833. Following the 1830 Indian Removal Act, Schoolcraft negotiated the 1836 Treaty of Washington which opened up the land north of Grand Rapids for unequivocal legal ownership and settlement of lands in Northern Michigan, with provision that land sales would provide some monetary means to fund skills training for the Natives to assimilate to "civilized" life.