It seems to be a well-known fact that the skin in certain individuals is abnormally sensitive to the chemical or actinic rays of light. As pointed out recently by Hyde,1 this hypersensitiveness may be evidenced in the production of either hyperemia, pigmentation, telangiectasis, atrophy, hyperkeratosis or cancerosis of the skin. At times, though rarely, these different forms of reaction to the same influences may occur in one and the same person and then occasionally in a regular order of succession. This is the case in the rare disease known as xeroderma pigmentosum, a disease of childhood; here hyperemia is followed by pigmentation of the exposed parts of the body and eventually telangiectasis, spots of atrophy and of warty outgrowths (hyperkeratosis) develop and finally typical, usually multiple carcinoma.
In adults analogous processes are relatively more frequent and develop usually after the middle periods of life. Hyde brings forward strong statistical