The present investigations deal with the question of whether contact X-ray irradiation as well as painting with methyicholanthrene and benzpyrene effect a change in the total phosphorus content of the epidermis of the treated area of the skin. METHOD The X-ray experiments were carried out on white male and female rats. One group of animals weighed 60 g, and the other group weighed 100-120 g. The hair was plucked on both the sides of the animals in round symmetrical areas, the diameters of which

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... were about 2.5 cm. On one of the areas X-ray irradiation was applied, the opposite side was used as control. The X-ray irradiation was done 9-11 days after the hair had been plucked. At this time, in the majority of the animals, the new hairs had not yet reached the surface of the skin, or were only just perceptible. (The animals in which the hairs were already a few mm long on the 9-11 day after the plucking were not used for the experiment.) The plucking was done so that the hair on the area of the skin of the animals used for the experiment would be approximately at the same stage of development since our preliminary experiments indicated that the reaction of the irradiated skin depends to a great extent upon the stage of the development of the hair. Each animal received a dose of 3000 r contact X-rays in one field. The irradiation was carried out by means of a Philips contact apparatus (2 mA, 50 kV and a focal distance of 20 cm) without using a filter. The examinations were carried out on the 2-7th day after the irradiation. At this time the hairs on the areas of the skin treated with X-rays, as well as on that of the controls, were already long enough to be plucked out with pincers. The loosening of the hairs on the sites treated with X-rays could be detected 2-3 days after the irradiation. The investigations concerning the action exerted by the carcinogenous hydrocarbons were carried out on domestically bred, light brown colored adult mice. Most of the animals were males, only a few of them females. The hairs of the animals were-at least apparently-in the resting stage. Animals showing signs that the hairs were in a stage of changing were not used. The skin of one side of the animals was painted on a round area 2 cm in diameter with a solution of 0.6 per cent of methylcholanthrene or 0.8 per cent of benzpyrene dissolved in benzeue, without the hair being sheared. Most of the animals were painted only once, in a few cases twice. The second painting, when done, was carried out on the 4th day after the first. The examinations were performed on the 1-6th day