False-colour scanning electron micrograph of the anaerobic spirochaete bacteria Treponema pallidum, the causative agent of syphilis in man. The bacteria are seen as the wavy & extended threads in a portion of a testicular cell four hours after infection. T. pallidum enters the body during sexual intercourse through the mucous membranes of the vagina or urethra. It may be transmitted by an infected pregnant woman across the placenta to her unborn child (congenital syphilis). The disease passes through three stages; tertiary syphilis may cause damage to the heart, blood vessels, brain & spinal cord. Blindness & insanity may result. Penicillin is effective if administered early on.