This disease, with its prolonged course and its final tendency to cancerous development, forms one of the most curious and most difficult problems of pathology. It seems to have as a predisposing cause a peculiar sensitiveness of the skin to sunlight. This is shown by the fact that it occurs in the parts of the skin exposed to the light, and that it usually commences in the second year of life, this being the time when children begin to run about and become more exposed to the sunlight. That this is a constitutional peculiarity appears from the frequency with which the disease occurs in several members of the same family.

The disease begins usually in spots of hyperemia on the exposed parts of the body, which assume the form of pigmented areas resembling ordinary freckles. There follow on this, usually in the course of years, various alterations in the skin in the form of slight warty projections, atrophic areas in which the skin is hard and tense, and local dilatations of the vessels. This goes on usually for years and is succeeded by a condition in which in one or more places the warty projections assume cancerous characters, the epidermic cells penetrating downwards into the cutis vera, in the manner of a regular epithelioma. The cancer ulcerates, and, as it extends at the same time, there may be very great destruction of the parts, even down to the bones. In a case seen after death by the author, there occurred destruction of almost the entire side of the face, along with large portions of the temporal bone and the superior and inferior maxilla?.

A somewhat analogous disease occurring in adults has been described by Unna with the name of Seaman's skin. In it the exposure to the weather sometimes induces in seamen a condition of cyanotic redness followed by pigmentation, thickening of the horny epidermis, etc. On this, at long intervals, follows the development of Ulcerating cancer, just as in the other case.