When syphilis is communicated from one individual to another by contact infection, the condition is spoken of as _acquired syphilis_, and the first visible sign of the disease appears at the site of inoculation, and is known as _the primary lesion_. Those who have thus acquired the disease may transmit it to their offspring, who are then said to suffer from _inherited syphilis_. #The Virus of Syphilis.#--The cause of syphilis, whether acquired or inherited, is the organism, described by Schaudinn and Hoffman, in 1905, under the name of _spirochæta pallida_ or _spironema pallidum_. It is a delicate, thread-like spirilla, in length averaging from 8 to 10 µ and in width about 0.25 µ, and is distinguished from other spirochætes by its delicate shape, its dead-white appearance, together with its closely twisted spiral form, with numerous undulations (10 to 26), which are perfectly regular, and are characteristic in that they remain the same during rest and in active movement (Fig. 36). In a fresh specimen, such as a scraping from a hard chancre suspended in a little salt solution, it shows active movements. The organism is readily destroyed by heat, and perishes in the absence of moisture. It has been proved experimentally that it remains infective only up to six hours after its removal from the body. Noguchi has succeeded in obtaining pure cultures from the infected tissues of the rabbit. [Illustration: FIG. 36.--Spirochæta pallida from scraping of hard Chancre of Prepuce. × 1000 diam. Burri method.] The spirochæte may be recognised in films made by scraping the deeper parts of the primary lesion, from papules on the skin, or from blisters artificially raised on lesions of the skin or on the immediately adjacent portion of healthy skin. It is readily found in the mucous patches and condylomata of the secondary period. It is best stained by Giemsa's method, and its recognition is greatly aided by the use of the ultra-microscope. The spirochæte has been demonstrated in every form of syphilitic lesion, and has been isolated from the blood--with difficulty--and from lymph withdrawn by a hollow needle from enlarged lymph glands. The saliva of persons suffering from syphilitic lesions of the mouth also contains the organism. [Illustration: FIG. 37.--Spirochæta refrigerans from scraping of Vagina. × 1000 diam. Burri method.] In tertiary lesions there is greater difficulty in demonstrating the spirochæte, but small numbers have been found in the peripheral parts of gummata and in the thickened patches in syphilitic disease of the aorta. Noguchi and Moore have discovered the spirochæte in the brain in a number of cases of general paralysis of the insane. The spirochæte may persist in the body for a long time after infection; its presence has been demonstrated as long as sixteen years after the original acquisition of the disease. In inherited syphilis the spirochæte is present in enormous numbers throughout all the organs and fluids of the body.