118 .JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (4) Wessells, N. K., Differentiation of epidermis and epidermal derivatives, New Engl. J. Med., 277, 21-33 (1967). (5) Billingham, R. E., and Medawar, P. B., Pigment spread and cell heredity in guinea- pigs' skin, Heredity, 2, 29-47 (1948). (6) Billingham, R. E., and Medawar, P. B., The technique of free skin grafting in mam- mals, J. Exp. Biol., 28, 385-402 (1951). (7) Russell, P.S., and Billingham, R. E., Some aspects of the repair process in mammals, Progr. Surg., 2, 1-72 (1962). (8) McMinn, R. M. H., Tissue Repair, Academic Press, New York, 1969. (9) Billingham, R. E., and Medawar, P. B., A note oxi the specificity of the corncal epi- thelium, J. dnat., 84, 50-6 (1950). (10) Krohn, P. L., The behaviour of autografts and homografts of vaginal tissue in rabbits, Ibid., 89, 269-82 (1955). (11) Montagna, W., The Structure and Function of Skin, Academic Press, New York, 1962. (12) Beer, A. E., and Billingham, R. E., hnplantation, transplantation, and epithelial- mesenchymal relationships in the rat's uterus, J. Exp. Med., 1•2, 721-36 (1970). (13) Cohen, J., Interactions in the skin, Brit. ]. Derrnatol., 81, Suppl. 3, 46-54 (1969). (14) Oliver, R. F., The vibrissa dermal papilla an,d its influence on epidermal tissues, Ibid., 81, Suppl. 3, 55 (1969). (15) Green, M. C., Mutant Genes and Linkages, in Green, E. I,, Biology of the Laboratory Mouse, McGraw-Hill, New York, 1966, pp. 87-150. (16) Shaffer, C. F., Billingham, R. E., and Mann, G., Work in progress, 1970. (17) Tsuji, S., and Yosida, T., Reciprocal skin transplantation between normal and hereditary hairless mice, Jap. J. Genet., 40, 50-62 (1965). (18) Medawar, P. B., Biological Effect of Heterologous Antilyrnphocyte Sera, in Rapaport, F. T., and Dausset, J., Human Transplantation, Grune and Stratton, New York, 1968, pp. 501-9. (19) Lance, E. M., and Medawar, P. B., Suiwival of skin heterografts under treatment with antilymph ocytic serum, Lancet, 1, 1174-6 (1968).

J. Soc. Cosmet. Chem., 22, 119-137 (Feb. 4, 1971) Barrier Development, Ultrastructure, and Sulfhydryl Content of the Fetal Epidermis EDWARD J. SINGER, Ph.D., PAUL C. WEGMANN, B.S., MARJORIE D. LEHMAN, B.S., MICHAEI, S. CHRISTENSEN, B.S., and LEONARD J. VINSON, Ph.D.* Presented May 26-27, 1970, New York City Synopsis--Previous studies have demonstrated that the PERMEABILITY BARRIER of the SKIN resides principally in the stratum comeurn and that in mammalian species this barrier is fully developed at birth. In the present study, development of the stratum comeurn was observed during fetal life of the rat and the guinea pig. Measurements were made of the water permeability of fetal skin at several periods in fetal life through tenn. At the same periods, tissues were examined for changes in fine STRUCTURE and in SULFHYDRYL CONTENT. The data revealed that genesis of the permeability barrier starts in the last quarter of gestation and is concluded just before term. Concurrent with the final stages of formation of the permeability barrier sulfur metabolism is intensified. The horny layer matures as evidenced by increased cellular cohesion and aggregation of tonofilaments into well-defined bundles differentiation of the stratum granulosum and stratum comeurn goes to completion. At birth, the ultrastructure of the stratum comeurn is indistinguishable from that of the adult. INTRODUCTION The skin in the mammal serves two primary "survival" functions, viz., to prevent desiccation of the organism, and to provide a barrier to *Skin studies described in this report were sponsored by U.S. Army Edgewood Arsenal (Contract No. DA 18-108-CML 6573), Edgewood Arsenal, Md. In conducting the research re- ported herein, the investigators adhered to the "Principles of Laboratory Animal Care" as established by the National Society for Medical Research. ? Lever Brothe•'s Co., Research and Development Division, Edgewater, N.J. 07020. 119