Reiter, Hans Conrad Julius (1881–1969), German bacteriologist. Reiter had a career both as a professor of hygiene at several German universities and as a government public health official. While serving with the German forces during World War I, he discovered the causative organism of Weil's disease. During the war he treated his first patient suffering from a disease marked by urethritis, conjunctivitis, and arthritis. This disease is now known as Reiter's syndrome. He published reports of his field hospital discoveries in 1916. He identified, named, and investigated the spirochete of the genus Treponema (T. pallidum) that causes syphilis in humans, and his discovery of a specific antigen for it led to his development of a complement-fixation test for syphilis. He also described the entoptic symptoms of digitalis intoxication and wrote an important monograph on the use of vaccines.