Body lice are voracious feeders, producing by their bites and the irritating saliva which they inject, rosy elevations and papules which become covered with a brownish crust. The intense itching provokes scratching, and characteristic white scars (fig. 67) surrounded by brownish pigment (fig. 68) are formed. The skin may become thickened and take on a bronze tinge. This melanoderma is especially marked in the region between the shoulders but it may become generalized, a prominent characteristic of "vagabond's disease." According to Dubre and Beille, this melanoderma is due to a toxic substance secreted by the lice, which indirectly provokes the formation of pigment. [Illustration: 67. Pediculosis in man caused by the body louse. After Morrow.] Control measures, in the case of the body louse, consist in boiling or steaming the clothes or in some cases, sterilizing by dry heat. The dermatitis may be relieved by the use of zinc-oxide ointment, to which Pusey recommends that there be added, on account of their parasiticidal properties, sulphur and balsam of Peru, equal parts, 15 to 30 grains to the ounce. _Phthirius pubis_ (= _P. inguinalis_), the pubic louse, or so-called "crab louse," differs greatly from the preceding in appearance. It is characterized by its relatively short head which fits into a broad depression in the thorax. The latter is broad and flat and merges into the abdomen. The first pair of legs is slender and terminated by a straight claw. The second and third pairs of legs are thicker and are provided with powerful claws fitted for clinging to hairs. The females (fig. 69) measure 1.5 to 2 mm. in length by 1.5 mm. in breadth. The male averages a little over half as large. The eggs, or nits, are fixed at the base of the hairs. Only a few, ten to fifteen are deposited by a single female, and they hatch in about a week's time. The young lice mature in two weeks. The pubic louse usually infests the hairs of the pubis and the perineal region. It may pass to the arm pits or even to the beard or moustache. Rarely, it occurs on the eyelids, and it has even been found, in a very few instances, occurring in all stages, on the scalp. Infestation may be contracted from beds or even from badly infested persons in a crowd. We have seen several cases which undoubtedly were due to the use of public water closets. It produces papular eruption and an intense pruritis. When abundant, there occurs a grayish discoloration of the skin which Duguet has shown is due to a poisonous saliva injected by the louse, as is the melanoderma caused by the body louse. [Illustration: 68. Melanoderma caused by the body louse. From Portfolio of Dermochromes, by permission of Rebman & Co., New York, Publishers.] The pubic louse may be exterminated by the measures recommended for the head louse, or by the use of officinal mercurial ointment. [Illustration: 69. Phthirius pubis. Ventral aspect of female. (×12).] HEMIPTERA