A 19th century illustration of an emaciated man suffering from syphilis. The caption reads: 'The dreadful result of visiting the seraglio'. Syphilis is caused by the bacterium Treponema pallidum, usually transmitted by sexual contact. It produces a sore followed by fever and swelling of the lymph glands. In the tertiary stage of infection the bacterium causes widespread permanent damage by the formation of chronic skin abcesses (gumma). In the 19th century mercury was often used to treat the disease despite its toxic side-effects. Without treatment, it may cause loss of voluntary movement control (locomotor ataxia) or insanity (dementia paralytica).