[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 µ 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 small groups or in short chains. Soft sores are always contracted by direct contact from another individual, and the incubation period is a short one of from two to five days. They are usually situated in the vicinity of the frænum, and, in women, about the labia minora or fourchette; they probably originate in abrasions in these situations. They appear as pustules, which are rapidly converted into small, acutely inflamed ulcers with sharply cut, irregular margins, which bleed easily and yield an abundant yellow purulent discharge. They are devoid of the induration of syphilis, are painful, and nearly always multiple, reproducing themselves in successive crops by auto-inoculation. Soft sores are often complicated by phimosis and balanitis, and they frequently lead to infection of the glands in the groin. The resulting bubo is ill-defined, painful, and tender, and suppuration occurs in about one-fourth of the cases. The overlying skin becomes adherent and red, and suppuration takes place either in the form of separate foci in the interior of the individual glands, or around them; in the latter case, on incision, the glands are found lying bathed in pus. Ducrey's bacillus is found in pure culture in the pus. Sometimes other pyogenic organisms are superadded. After the bubo has been opened the wound may take on the characters of a soft sore.