_Every case of acquired syphilis begins with an initial sore_, though this may be so located or so complicated with some other lesion as to be overlooked. The character of the induration varies somewhat with the location, _i. e._, whether upon the skin or mucous membrane. The amount of moisture or maceration to which it is exposed will also influence its appearance. It may be minute, so as to almost elude observation even on visible parts, or it may spread and involve an area 1 Cm. in diameter. The lesion is _usually solitary_, but when several abraded spots are infected at the same time there may be multiple sores. When a surgeon sees a lesion of this character it has usually changed its original appearance--perhaps by some previous treatment, perhaps by maceration. There is one invariable feature upon varying expressions of which diagnosis is based, and that is _induration_. The instances in which this fails are very rare; on the other hand, it is possible that it may be the result of treatment already undergone, and for this reason the recent history of the case should be obtained; in other words, _the typical chancroid is always indurated_, but an indurated sore does not of itself necessarily indicate syphilis if it can be satisfactorily accounted for in other ways. The presence of an active primary lesion seems to confer immunity to subsequent infection for a period co-equal with the active manifestations of the disease, although even in this respect exceptions are occasionally to be noted. The induration of syphilis develops beyond and beneath the limits of the superficial lesion, and gives the sensation, when grasped between the fingers, of a piece of firm material embedded in the skin or membrane. It is firm, slightly elastic, with usually well-defined boundaries, which accounts for the expression, _parchment induration_. Ordinarily no pain or other sensations accompany its formation or attract attention; hence the frequency with which it escapes observation for some time and the uncertainty which the patient feels regarding the dates. The surface of the induration usually becomes moist or abraded and frequently ulcerated; but these surface lesions tend eventually to heal, even if let alone, except in those parts, _e. g._, the lips, where they are constantly bathed by discharge. The characteristic induration disappears slowly in a few weeks or months, leaving ordinarily no trace of its existence, although sometimes a small scar, occasionally pigmented, is left to mark its site. There are two or three classical varieties of chancre which deserve more minute description. As ordinarily seen upon the genitalia, a chancre may assume the following types: A. Dry, scaly papule. B. Superficial erosion. C. Hunterian, or ulcerating chancre.