Within certain limits the specific infection of syphilis, or, as it is frequently spoken of, the specific disease, passes through a somewhat regular program in which periods of activity and latency seem to alternate. The first visible lesion is at the point of entrance of the virus, in acquired cases, after a certain period of incubation, and is known always as the _chancre_. Of course, in inherited syphilis no chancre or primary sore is found. Then occurs a second period of incubation, during which there is a still more widespread general infection of the body, in which at first the lymphatic system seems to suffer most. This is characterized by a certain degree of fever, progressive anemia, malaise, tenderness and pain in bones and joints, all of which indicate a _progressive toxemia_. =Manner of Contagion.=--The manner of contagion in acquired cases is naturally most often that of the sexual act, although contagion may come from many sources, including unclean utensils, pipes, etc., as well as the instruments of the dentist or the surgeon. Some abrasion of the infected surface is almost invariably presupposed, since it is not established that the virus of syphilis will enter an unbroken surface, though it may lurk thereon; but the abrasion may be trifling and occur in such situation, especially on the female genitalia, as to be undiscoverable or unnoticed. It is then possible that patients may speak truthfully when denying the existence in the past of any venereal sores. The transmission of infection from parent to offspring in the uterus will be discussed later. =Nature of the Virus.=--That syphilis is a disease of parasitic character, _i. e._, _contagious_, there can, of course, be no question. The nature of the _contagium vivum_ which produces these changes, long unknown, is now believed to be revealed in the _spirochæta pallida_ recently described by Schaudinn and others; an organism 4 to 10 μ in length, ¹⁄₂ μ in width, possessing several curves like those of a corkscrew, with sharpened poles, mobile, its motions consisting of rotations and bendings. It has been demonstrated that primary lesions contain the organism, either constantly or in the majority of cases, while in skin and nearly all other lesions it can be also shown (Fig. 23). [Illustration: FIG. 23 Spirochæta pallida (syphilis) in adrenal of child with congenital syphilis. (Gaylord.)]