080 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS exhibits characteristic absorption bands in the visible. Yet, its isoelec~ tric point may be 7 or 4.3, depending on the proportion of chromophore it may contain varying amounts of amino acids and have more or less developed indicator properties, vivid colors, and sharp absorption bands. Therefore, it is essential that confusion in terminology be avoided. The pigments with neutral isolelectric points originally extracted with acids are called the siderins, their protein-free parts the chromophores all "intermediate" compounds between these two will be referred to as chromophore peptide complexes. Far-reaching purification of the chromophore was obtained by B oldt in his recent work (11). The most purified material consisted of a mix- ture of a large number of closely related compounds, many of which were interchangeable under the influence of light and changes in pH. As they had similar absorption spectra, C, H, N, O, and S contents, and equivalent weights, based on titration, they could be distinguished by their char- acteristic R s values and colors on Sephadex G-25 columns. These chromophores are free of iron. None of the findings so far support the view that the red hair pigment is produced by tyrosinase activity. Heretofore, negative findings in this area have been dismissed as the result of inadequate techniques. The problem of the red and yellow pigments, the misnamed "pheomelanins," should be reinvestigated with an open mind the many areas in need of intensive research have been outlined in another publication (12). ADDENDUM After completion of this manuscript, a pigment was isolated from the fur of New Zealand red rabbits which in preliminary tests exhibited the same features as the iron pigments of red hair and feathers. Rabbit fur resembled feathers inasmuch as its red pigment could be extracted in relatively large quantities within 15 minutes with boiling 0.1 N HC1. Thus, the epidermal iron pigments appear to be of general biologic im- portance. Their discovery in a laboratory animal should facilitate further chemical and biologic studies. (Received January 24, 1968) •REFERENCES (1) Rothman, S., and Flesch, P., Isolation of an iron pigment from human red hair, Proc. Soc. Exptl. Biol. ivied., 53,134-5 (June 1943). (2) Flesch, P., and Rothman, S., Isolation of an iron pigment from human red hair, J. Invest. Dermatol., 6, 257-70 (August 1945).

IRON PIGMENTS OF HAIR AND FEATHERS 681 (8) Flesch, P., Esoda, E. J., and Katz, S. A., The iron pigment of red hair and feathers, Ibid., 47, 595-7 (December 1966). (4) Zelickson, A. S., Ultrastructure of Normal and Abnormal Skin, Lea & Febiger, Phila- delphia, Pa., 1967, p. 169. (5) Fitzpatrick, T. B., et al., The Nature of Hair Pigment, in Montagna, W., and Ellis, R. A., Biology of Hair Growth, Academic Press, New York, N.Y., 1958, pp. 255-301. (6) Aisen, P., Aasa, R., Malmstr6m, B. G., and Vanngard, T., Bicarbonate and the binding of iron to transferrim J. Biol. Chem., 242, 2484-90 (May 25, 1967). (7) Warner, R. C., and Weber, 1., The metal combining power of conalbumin, J. Am. Chem. Soc., 75, 5094-101 (October 20, 1953). (8) Fukuyama, K., and Epstein, W. L., Epidermal keratinization: Localization of iso- topically labeled amino acids, J. Invest. Dermatol., 47,551--60 (December 1966). (9) Flesch, P., Esoda, E. J., and Katz, S. A., The color of red hair, J. Soc. Cosmetic Chemists, 18, 777-84 (December 1967). (10) Boldt, P., Trichosiderin, ein Pigment aus roten Haaren, Naturwissenschaften, 51, 265 (June 1964). (11) Boldt, P., and Hermstedt, E., Pyrrotrichole, eine Gruppe farbiger Verbindungen aus rotem Menschenhaar, Z. Naturforsch., 22b, 718-22 (July 1967). (12) Flesch, P., and Esoda, E. J., The pigmentation of red hair, Dermatology Digest, 7, 49-44 (1968).