Frederick A. Castle interrupted his studies at the Bellevue Medical College in New York to join the newly-formed Medical Cadet Corps of the U.S. Army Medical Department in 1861. He also served for two years in the Navy before the Civil War ended. He received his M.D. from Bellevue Medical College in 1866. He occupied, for a time, the chair of therapeutics at Bellevue and also worked as a visiting physician at Presbyterian hospital. Castle was an active editor of medical journals throughout his career.
From the description of Frederick Augustus Castle papers, 1862-1902. (National Library of Medicine). WorldCat record id: 14318241
From the guide to the Frederick Augustus Castle Papers, 1862-1902, (History of Medicine Division. National Library of Medicine)