SKIN AND HAIR PIGMENTATION 209 in individuals with red or strawberry blond hair. Therefore, there is good reason to suspect that red hair pigment formation involves biochemical pathways other than just the tyrosinase-tyrosine reaction. In closing, it is amusing to speculate rather wildly about the possibility that the greater temperamentality popularly supposed to be associated with red hair might perhaps some day actually find a basis in a biochemical difference in trypto- phane metabolism in such individuals, since tryptophane is also the source of 5-hydroxytryptarnine, which has important roles in brain function as revealed by modern psychopharmacologic studies. [Received: 31st December 1957] REFERENCES* Edwards, E. A., and Duntley, S.Q. Arner. J. zinat., 1939, 6õ, 1-33. Edwards, E. A., Hamilton, J. B., Duntley, S. Q., and Hubert, G. 2•ndocrinology, 1941, gS, 119-28. Hall, T. C., McCracken, B. H., and Thorn, G.W.J. clin. 2•ndocrin., 1953, 18, 243-57. Jesionek, A. Biologic der gesunden und kranken Haut, 1916. (Leipzig: F. C. W. Vogel.) Sumner, F.B. Cited by Lorus, J., and Milne, M.J. Sci. Arner., 1952, 186, 64-7. Eppinger, H. Biochem. Z., 1910, gS, 181-92. Becker, S. W., Jr., Fitzpatrick, T. B., and Montgomery, H. Arch. Derrn. Syph., N.Y., 1952, õõ, 511-23. Taylor, A.C.J. exp. Zool., 1949, 110, 77-112. Liebow, A. A., Warren, S., and De Coursey, E. Arner. J. Path., 1949, gõ, 853-1027. Masson, P., Miner, R. W. (ed.). The biology of melanornas, 1948, 15-51, "Special . publications of the New York Academy of Sciences," 4. (New York: The Academy.) - Billingham, R. E., and Medawar, P. B. Phil. Trans., 1953, g37, 151-71. Birbeck, M. S.C. •/he Electron Microscopy of the Melanocyte and the Spread of Pigrnent. 1957 Symposium on The Biology of Hair Growth, London. (To be published.) Mason, H. S., Kahler, H., MacCardle, R. C., and Dalton, A. J. Proc. Soc. exp. Biol., N.Y., 1947, õõ, 421-31. Greenstein, J. P., Turner, F. C., and Jenrette, W. V. J. nat. Cancer Inst., 1940, 1, 377-85. Raper, H.S. Physiol. Rev., 1928, 8,245-82. Lerner, A. B., Fitzpatrick, T. B., Calkins, E. and Summerson, W. H. J. Biol. Chern., 1949, 178, 185-95 1950, 187, 793-802 and 1951, 1Ol, 799-806. Lerner, A. B. Arner. J. Me, d., 1955, 19,902-24. Wilkinson, J. F., and Ashford, C.A. Lancet, 1936, •, 967-70. Rothman, S., Krysa, H. F., and Smiljanic, A.M. Proc. Soc. exp. Biol., N.Y., 1946, 6g, 208-9. Fitzpatrick, T. B., Becker, S. W., Jr., Lerner, A. B., and Montgomery, H. Science, 1950, 11•, 223-25. Magnin, P. H., and Rothman, S. Dermatologica, Basel, 1957, 115, 315-320. Miyamoto, M., and Fitzpatrick, T. B. Nature, Lond., 1957, 179, 199-200. Oliver, E. A., Schwartz, L., and Warren. L. H. •trch. Derrn. Syph., N.Y., 1940, 993-1014. Harris, J. I., and Lerner, A.B. ivature, Lond., 1957, 179, 1346-7. Lerner, A. B., and Lee, T.H.y. •trner. chern. Soc., 1955, 77, 1066-7. Lee, T. H., and Lerner, A.B.J. biol. Chern., 1956, ggl, 943-959. Geschwind, I. I., Li, C. H., and Barnaft, L. J. Amer. chern. Soc., 1956, 78, 4494-5. Geschwind, I. I., Li, C. H., and Barnaft, L. J. Arner. chern. Soc., 1957, 79, 620-25. Lerner, A. B., Shizume, K., and Fitzpatrick, T. B. J. inoest. Derrn., 1953, gl, 337-8. Frieden, E. H., and Bozer, J.M. Proc. Soc. exp. Biol., 1V.Y., 1951, ??, 35-7. Lynn, W. G., and De Marie, A. Science, 1946, 104, 31. Trinkaus, J.P. Gordon, M. (ed.). Pigment cell growth, 1953, 73-92. (New York: Academic Press, Inc.) Davis, M. E., Boynton, M. W., Ferguson, J. H., and Rothman, S. J. clin. 2•ndocrin, 1945, õ, 138-46. Pfeiffer, C. A., Hooker, C. W., and Kirschbaum, A. Endocrinology, 1944, •4, 389-99.

210 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS a5 Kupperman, H.S. A nat. Rec., 1944, 88, 442. a• Hamilton, J. B., and Hubert, G. Science, 1938, 88, 481. a? NicheIls, L. Lancet, 1946, g, 201. as Frost, D.V. Physiol. Rev., 1948, gS, 368-82. a9 Zarafonetis, C. J.D.J. invest. Derrn., 1950, 1õ, 399-401. 40 Keil, H. L., and Nelson, V. E. J. biol. Chern., 1931, 93, 49-57. 4• Gorter, F. J. Nature, Lend., 1935, 11•õ, 185. 4• Ire, M. Tohoku J. exper. Med., 1952, õõ (suppl. 1), 101. 49 Henschke, V., and Schulze, R. Strahlentherapie, 1939, {14, 14-42. 44 Blum, H.F. Physiol. Rev., 1945, gõ, 483-529. 45 Fitzpatrick, T. B. The Nature of Hair Pigments. 1957 Symposium on The Biology of Hair Growth, London. (To be published.) 4• Flesch, P., and Rothman, S. J. invest. Derrn., 1945, {1, 257-70. * Much of the material covered in this presentation has appeared in the chapter on Pigmentation by the author in: Rothman, S., Physiology and Biochemistry of the Skin, 1954, 515--63. (Chicago: The University of Chicago Press.) PRESERVATION OF TOILET PREPARATIONS CONTAINING NONIONICS DOREEN L. WEDDERBURN, B.Sc.* Based on • lecture delivered before the Society on 29th November 1957. The effect of nonionic materials on preservatives has been studied thirty-six nonionics and twenty-six preservatives were used in the investiga- tion. The nonionic surfactants reduced the efficiency of all the preservatives when the ratio of surfactant to preservative exceeded certain critical values, whereas non-surface-active nonionics did not. The critical ratio varies for each preservative and is dependent on the amount and type of nonionic sur- factant present. The possibility that certain nonionic surfactants protect micro-organisms, rendering them more resistant to preservatives, is also discussed. INTRODUCTION FOR MANY years soaps and anionic detergents have been used in toilet preparations as emulsifiers or on account of their cleansing properties. Preservatives were normally added to these products and adequate preserva- tion was not difficult. In recent years, nonionic surfactants have been increasingly used in toilet preparations, particularly as emulsifiers, solubil- isers and lather boosters. Because they have several advantages over anionic materials, nonionics are largely replacing the more conventional materials as emulsifiers in toilet preparations. As a result of using these materials the pH of products containing them is often lower than when soaps are used. Previously, almost all cosmetic creams were alkaline and did not provide environments particularly suited to the growth of micro-organisms, so that only mildly bacteriostatic or fungistatic preservatives were often adequate, but, when nonionics are * Unilever Ltd., Toilet Preparations Development Unit, Isleworth, Middlesex.