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 oedematous 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 phagedaena.  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.

[Illustration:  FIG. 38.—­Primary Lesion on Thumb, with Secondary Eruption on Forearm.[1]]

[1] From A System of Syphilis, vol. ii., edited by D’Arcy Power and J. Keogh Murphy, Oxford Medical Publications.

#The Soft Sore, Soft Chancre, or Chancroid.#—­The differential diagnosis of syphilis necessitates the consideration of the soft sore, soft chancre, or chancroid, which is also a common form of venereal disease, and is due to infection with a virulent pus-forming bacillus, first described by Ducrey in 1889.  Ducrey’s bacillus occurs in the form of minute oval rods measuring about 1.5 [micron] in length, which stain readily with any basic aniline dye, but are quickly decolorised by Gram’s method.  They are found mixed with other organisms in the purulent discharge from the sore, and are chiefly arranged in