Syphilis is a sexually transmitted disease, and since most couples have genital sex, the primary lesion of syphilis, which is called a chancre, usually develops on a man’s penis or on a woman’s vulva. However, in about 25 per cent of women, the primary lesion develops on her cervix and is invisible, but highly infectious should she have sexual intercourse with an uninfected partner. Without treatment, the person who has syphilis remains infectious for about two years, after which the chance of infecting another person diminishes. The organism which causes syphilis is a tiny slender corkscrew-shaped organism which is invisible to the naked eye. It 0 measures about 2.0µ in length. А µ (pronounced mew) is one-thousandth of a millimetre in length, so that 500 organisms placed end to end would be needed to measure one centimetre, and 1250 to measure an inch. The organism is called Treponema pallidum, and it is coiled along its 20µ length. Usually there are about twelve coils. The Treponema pallidum can only live in the moist warm atmosphere of the human body, and dies within a very few hours outside it. But once inside the body it thrives.