=Symptoms of the Ulcer.=--In all probability the initial sore and the ensuing lymphatic involvement are due to the parasite and to its toxic products. These latter are quickly taken into the general circulation and are held to confer the immunity which syphilitics enjoy before the outbreak of the general eruption. Anemia, malaise, and other like symptoms are evidences of a progressive intoxication or toxemia, while the earlier eruptions, which tend to evince the contagious element in a rather virulent form, may be due to the germs alone, or combined with their toxins. On this hypothesis can be explained the partial or complete immunity evinced by mothers who bear syphilitic children, the infection coming from the father. From the first evidence of infection the whole syphilitic process gives evidence of its infectious character. The bloodvessel walls undergo a thickening of their coats and more or less obliteration of their lumen, and this, of course, causes a disturbance in the nutrition of the parts supplied by them. This vascular change can be recognized even in the minute vessels of the initial lesion, and thereafter pertains to most if not all specific manifestations of the disease. Our knowledge of the nature of this disease would be more complete were it possible to convey it to animals, but these are practically exempt from it, for the few and rare instances where, it is said, the disease has been inoculated upon the higher quadrumana furnish insufficient data. In this respect the disease is like the exanthemas, of whose parasitic origin there can be no question. _The First Period of Incubation and the Chancre._--The time which elapses between the exposure and the first appearance of the initial lesion is known as the _first period of incubation_. _This varies, within wide limits, from ten days to forty or fifty_; some writers have made it even seventy days. The average period varies from three to four weeks. There is often uncertainty as to when the induration began, and patients, women especially, may easily make a mistake of several days in fixing this date.