342 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS at pH 7.0 in phosphate buffer. The amount of both proteins obtained by the successive extraction procedure decreased with each successive extrac- tion. The second and third extraction of the epidermis with a 6 M urea solution yielded only the fibrous protein, whereas these extractions with a 2 M urea solution gave both proteins. 3. Six or 10 M urea solutions gave extracts of beef snout epider- mis which yielded clots following dialysis of the extracts against distilled water. Clots were not formed following dialysis of 0.5, 1.0 and 2.0 M urea extracts of epidermis against distilled water. The concentrated urea solu- tions apparently extract more complex keratin precursors l¾om the upper strata of the epidermis. 4. The protein material of the clots which was obtained following dialy- sis of the 6 and 10 M urea epidermal extracts against distilled water and the insoluble proteins of isoelectric point of pH 6.3 which was acquired fol- lowing acidification of the dialysis sac contents appear to be of somewhat similar composition. This is so because they were both cleaved by 6 NI'urea solutions to give the fibrous and non-fibrous proteins. The mobility of the proteins obtained from the insoluble proteins of isoelectric point of pH 6.3 was significantly higher than that obtained by direct extraction of the epi- dermis or from the clot. 5. Histological examination of beef snout epidermis left in 6 M urea solutions for periods from one to twenty-four hours revealed that this solu- tion dissolved, along with other cellular components, the tonofibrils. The granular layer of the epidermis and the keratin coat appeared to be intact histologically. 6. Possible changes in the structural proteins of epidermis with age are briefly discussed. REFERENCES (1) Cowdry, E. V., Cooper, Z. K., and Smith, W., "Program of Research on Ageing of the Skin," f. GerontoA, 2, 31 (1947). (2) Cooper, Z. K., and Schiff, A., "Mitotic Rhythm in Human Epidermis," Pro½. So½• Exp. Biol. Med., 39, 323 (1938). (3) Cooper, Z. K., "Mitotic Rhythm in Human Epidermis," a•. Investigative Dermatol., 2, 259 (1939). (4) Thuringer, J. M., "Studies on Cell Division in the Human Epidermis," .4nat. Record, 40, 1 (1928). (5) Cowdry, E. V., and Thompson, H. C., Jr., "Localization of Maximum Cell Division in Epidermis," Ibid., 88, 403 (1944). (6) Cooper, Z. K., "Ageing of Skin," Cowdry's Problems of Ageing, Third Edition. Balti- more, The Williams and Wilkins Company (1952), p. 764. (7) Evans, R., Cowdry, E. V., and Neilson, P. E., "Ageing of Human Skin. I. Influence of Dermal Shrinkage on Appearance of the Epidermis in Young and Old Fixed Tissue," .4nat. Record, 86, 545 (1943). (8) Ejiri, I., "Studien fiber die Histologie der menschlichen Haut. III," a•. Dermatol. Urol. [•apan], 41, 8 (1937). (9) Hill, R., and Montgomery, H., "Regional Changes and Changes Caused by Age in the Normal Skin. A Histologic Study," a•. Investigative Dermatol., 3, 231 (1940). (10) Thuringer, J. M., and Cooper, Z. K., "The Mitotic Index of the Human Epidermis, the Site of Maximum Cell Proliferation and the Development of the Epidermal Pattern," •lnat. Record, 106, 89 (1950).

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