Late in the 1918 season, Mathewson enlisted in the United States Army for World War I. His wife Jane was very much opposed to the decision, but Mathewson insisted on going [REF].
Although he returned to serve as a coach for the Giants from -, he spent a good portion of that time in Saranac Lake fighting the illness, initially at the Trudeau Sanitorium, and later in a house that he had built [REF].