626 J. A. A. Hunter development. Most of the melanosomes in keratinocytes appear disposed individually rather than in complexes (Fig. 5) (17). Wolff and Konrad (18, 19) have shown, both experimentally (using latex beads in guinea pig skin) and in human pigmentary dis- orders, that the complexing of melanosomes in keratinocytes is a size-dependent pheno- menon. Particles of 0.1 I• tended to be complexcd whilst those with a diameter of 0.8 I•m were not. CAUCASOlD KERA]'INOCY]'E NEGROID KERATINOCYTE Figure 8. Racial differences in melanosomal packaging. The smaller melanosomes in the Caucasoid keratinocyte are usually complexed whereas the larger ones in the Negroid tend to be disposed individually. REFERENCES 1 Findlay, G. H. Blue Skin. Brit. J. Derrn. 83 127 (1970). 2 Bloch, B. Chemische Untersuchungen fiber das spezifische pigmentbildende Ferment der Haut, die Dopa oxidase. Zeitschr. f. physiol. Chern. xcviii 226 (1917). 3 Becker, S. W. Praver, L. L. and Thatcher, H. An improved (paraffin section) method for the Dopa reaction. With considerations of the dopa-positive cell, as studied by this method. Arch. Derrn. Syoeh. 31 190 (1935). 4 Masson, P. Pigment cells in Man. In: The Biology of Melanomas. IV. Miner, R. W. and Gordon, M., Eds, Special publication, New York Academy of Sciences, 1948, p. 15. 5 Fitzpatrick, T. B., Becker, S. W. Jr., Lerner, A. B. and Montgomery, H. Tyrosinase in Human Skin: Demonstration of its presence and of its Role in Human Melanin Formation. Science, 112 223 (1950). 6 Billingham, R. E. Dendritic Cells. J. Artat. 82 93 (1948). 7 Cruickshank, C. N. D. and Harcourt, S. A. Pigment Donation in vitro. J. invest. Derrn. 42 183 (1964). 8 Fitzpatrick, T. B. and Breathnach, A. S. Das epidermale Melanin-Einheit-system. Derrn. Wschr. 147 481 (1963). 9 Rawles, M. E. Origin of melanophores and their r61e in development of color patterns in vertebrates. Physiol. Rev. 28 383 (1948). 10 Breathnach, A. S. and Wyllie, L. M. Electron Microscopy of Melanocytes and Langerhans cells in Human Fetal Epidermis at fourteen weeks. J. Invest. Derrn. 44 51 (1965). 11 Duchon, J., Fitzpatrick, T. B. and Seiji, M. Melanin some definitions and problems. In: Year Book ofDerrnatology. Kopf, A. W. and Andrade, a d R., Eds, Year Book Medical Publishers, Chicago, 1968, p. 6. 12 Drochmans, P. Ultrastructure of melanin granules. In: Advances in Biology of Skin: The Pig- rnentary System. VIII. Montagna, W. and Hu, F., Eds, Pergamon Press, Oxford, 1967, p. 169,

Causes of skin colouration 627 13 Fitzpatrick, T. B., Quevedo, W. C. Jr., Szabo, G. and Seiji, M. Biology of the melanin pigmentary system. In: Dermatology in General Medicine. Fitzpatrick, T. B., Arndt, K. A., Clark, W. H., Eison, A. Z., 'Van Scott, E. J. and Vaughan, J. H., Eds, McGraw Hill, New York, 1971, p. 117. 14 Seiji, M., Fitzpatrick, T. B. and Birbeck, M. S.C. The Melanosome: a distinctive subcellular particle of mammalian melanocytes and the site of melanogenesis. J. invest. Derre. 36 243 (1961). 15 Maul, G. G. Golgi-melanosome relationship in human melanoma in vitro. J. ultrastruct. Res. 26 163 (1969). 16 Hunter, J. A. A., Mottaz, J. H. and Zelickson, A. S. Melanogenesis: ultrastructural histochemical observations on ultraviolet irradiated human melanocytes. J. invest. Derrn. 54 213 (1970). 17 Szabo, G., Gerald, A. B., Pathak, M. A. and Fitzpatrick, T. B. Racial differences in the fate of melanosomes in human epidermis. Nature, 222 (1969). 18 Wolff, K. and Konrad, K. Phagocytosis of latex beads by epidermal keratinocytes in vivo. J. ultrastruct. Res. 39 262 (1972). 19 Konrad, K. and Wolff, K. Hyperpigmentation, melanosome size, and distribution patterns of melanosomes. Arch. Derre. 107 853 (1973). 20 Billingham, R. E. Dendritic cells in pigmented human skin. J. Anat. 83, 109 (1949).