Dr. Henry S. Tanner (1831 - 1919) was an American doctor, known for his great fast in New York in 1880.
On June 28, 1880, Tanner began a forty days' fast at Clarendon Hall in New York. After originally intending to go without food or water, he was persuaded to drink, before going without water from the second to the tenth day. Tanner lost almost 40 pounds by the conclusion of the experiment, and against the advice of his doctors began consuming meat, fruits, wine and milk immediately after. Tanner's fame in the coming decades was enough for Mark Twain to mention in passing that "I think that the Dr. Tanners and those others who go forty days without eating do it by resolutely keeping out the desire to eat, in the beginning, and that after a few hours the desire is discouraged and comes no more" in Following the Equator: A Journey Around the World in 1897.