Primary Syphilis.The period of incubation represents the interval that elapses between the occurrence of infection and the appearance of the primary lesion at the site of inoculation. Its limits may be stated as varying from two to six weeks, with an average of from twenty-one to twenty-eight days. While the disease is incubating, there is nothing to show that infection has occurred.

The Primary Lesion.—The incubation period having elapsed, there appears at the site of inoculation a circumscribed area of infiltration which represents the reaction of the tissues to the entrance of the virus. The first appearance is that of a sharply defined papule, rarely larger than a split pea. Its surface is at first smooth and shiny, but as necrosis of the tissue elements takes place in the centre, it becomes concave, and in many cases the epithelium is shed, and an ulcer is formed. Such an ulcer has an elevated border, sharply cut edges, an indurated base, and exudes a scanty serous discharge; its surface is at first occupied by yellow necrosed tissue, but in time this is replaced by smooth, pale-pink granulation tissue; finally, epithelium may spread over the surface, and the ulcer heals. As a rule, the patient suffers little discomfort, and may even be ignorant of the existence of the lesion, unless, as a result of exposure to mechanical or septic irritation, ulceration ensues, and the sore becomes painful and tender, and yields a purulent discharge. The primary lesion may persist until the secondary manifestations make their appearance, that is, for several weeks.

It cannot be emphasised too strongly that the induration of the primary lesion, which has obtained for it the name of “hard chancre,” is its most important characteristic. It is best appreciated when the sore is grasped from side to side between the finger and thumb. The sensation on grasping it has been aptly compared to that imparted by a nodule of cartilage, or by a button felt through a layer of cloth. The evidence obtained by touch is more valuable than that obtained by inspection, a fact which is made use of in the recognition of concealed chancres—that is, those which are hidden by a tight prepuce. The induration is due not only to the dense packing of the connective-tissue spaces with lymphocytes and plasma cells, but also to the formation of new connective-tissue elements. It is most marked in chancres situated in the furrow between the glans and the prepuce.

In the male, the primary lesion specially affects certain situations, and the appearances vary with these: (1) On the inner aspect of the prepuce, and in the fold between the prepuce and the glans; in the latter situation the induration imparts a “collar-like” rigidity to the prepuce, which is most apparent when it is rolled back over the corona. (2) At the orifice of the prepuce the primary lesion assumes the form of multiple linear ulcers or fissures, and as each of these is attended with infiltration, the prepuce cannot be pulled back—a condition known as syphilitic phimosis. (3) On the glans penis the infiltration may be so superficial that it resembles a layer of parchment, but if it invades the cavernous tissue there is a dense mass of induration. (4) On the external aspect of the prepuce or on the skin of the penis itself. (5) At either end of the torn frænum, in the form of a diamond-shaped ulcer raised above the surroundings. (6) In relation to the meatus and canal of the urethra, in either of which situations the swelling and induration may lead to narrowing of the urethra, so that the urine is passed with pain and difficulty and in a minute stream; stricture results only in the exceptional cases in which the chancre has ulcerated and caused destruction of tissue. A chancre within the orifice of the urethra is rare, and, being concealed from view, it can only be recognised by the discharge from the meatus and by the induration felt between the finger and thumb on palpating the urethra.

In the female, the primary lesion is not so typical or so easily recognised as in men; it is usually met with on the labia; the induration is rarely characteristic and does not last so long. The primary lesion may take the form of condylomata. Indurated œdema, with brownish-red or livid discoloration of one or both labia, is diagnostic of syphilis.

The hard chancre is usually solitary, but sometimes there are two or more; when there are several, they are individually smaller than the solitary chancre.

It is the exception for a hard chancre to leave a visible scar, hence, in examining patients with a doubtful history of syphilis, little reliance can be placed on the presence or absence of a scar on the genitals. When the primary lesion has taken the form of an open ulcer with purulent discharge, or has sloughed, there is a permanent scar.

Infection of the adjacent lymph glands is usually found to have taken place by the time the primary lesion has acquired its characteristic induration. Several of the glands along Poupart's ligament, on one or on both sides, become enlarged, rounded, and indurated; they are usually freely movable, and are rarely sensitive unless there is superadded septic infection. The term bullet-bubo has been applied to them, and their presence is of great value in diagnosis. In a certain number of cases, one of the main lymph vessels on the dorsum of the penis is transformed into a fibrous cord easily recognisable on palpation, and when grasped between the fingers appears to be in size and consistence not unlike the vas deferens.

Concealed chancre is the term applied when one or more chancres are situated within the sac of a prepuce which cannot be retracted. If the induration is well marked, the chancre can be palpated through the prepuce, and is tender on pressure. As under these conditions it is impossible for the patient to keep the parts clean, septic infection becomes a prominent feature, the prepuce is œdematous and inflamed, and there is an abundant discharge of pus from its orifice. It occasionally happens that the infection assumes a virulent character and causes sloughing of the prepuce—a condition known as phagedæna. The discharge is then foul and blood-stained, and the prepuce becomes of a dusky red or purple colour, and may finally slough, exposing the glans.

Extra-genital or Erratic Chancres ([Fig. 38]).—Erratic chancre is the term applied by Jonathan Hutchinson to the primary lesion of syphilis when it appears on parts of the body other than the genitals. It differs in some respects from the hard chancre as met with on the penis; it is usually larger, the induration is more diffused, and the enlarged glands are softer and more sensitive. The glands in nearest relation to the sore are those first affected, for example, the epitrochlear or axillary glands in chancre of the finger; the submaxillary glands in chancre of the lip or mouth; or the pre-auricular gland in chancre of the eyelid or forehead. In consequence of their divergence from the typical chancre, and of their being often met with in persons who, from age, surroundings, or moral character, are unlikely subjects of venereal disease, the true nature of erratic chancres is often overlooked until the persistence of the lesion, its want of resemblance to anything else, or the onset of constitutional symptoms, determines the diagnosis of syphilis. A solitary, indolent sore occurring on the lip, eyelid, finger, or nipple, which does not heal but tends to increase in size, and is associated with induration and enlargement of the adjacent glands, is most likely to be the primary lesion of syphilis.