RED PIGMENTARY SYSTEM 81 "red-orienting" (presumably cysteine-rich) milieu and thus prevents dopa from forming black melanin. Conversely, increased feather growth from thyroxine can convert red feathers to black (13), perhaps by allowing them to escape "way-laying" by cysteine. A similar process may account for the red discoloration of the hair of starving black children as in Biafra.* However, the nature of the red pigment in kwashiorkor is still unknown and therefore this mechanism is speculative. The change from red to black may be induced in vitro by overwhelm- ing the cells with dopa (dopa-positivity) or in vivo by purely local means. By daily proh)nged rubbing of New Zealand red rabbits with a neutral ointment we caused increased hair gTowth. During these periods of irri- tation the rabbits produce black hair on areas where normally only red hair grows (Fig. 2). ?•' Figure 2. Right: Black hand formed in hair of New Zealand red rabbit during period of local irritation by rubbing. Left: Control hair The switch between black and red pigment production is the physio- logic way in which agouti color arises in some black and orange animals. Accordingly, we were able to obtain typical siderin-like indicator pig- ments from the orange portion of the hair of golden hamsters no red * The question may be raised as to how a protein-deficient diet could provide the cysteine required for this mechanism. It should be rememhered that hair has an enormous avidity for sulfur-containing amino acids, a circumstance which may explain the normal cysteine of the hair of children suffering from kwashiorkor.

82 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS pigments could be extracted from the black sections. A similar sequence of events occurs in the Norwegian rat. Of the agouti animals, the mouse has been the subject of thorough studies by Cleftmann. Both yellow and black melanocytes of this species are converted to black-producing cells in tissue culture. Glutathione restores the yellow pigment production the amounts required are governed by genetic factors (14). During the yellow phase more sulf- hydryl was taken up by the pigment cells in the black stage the in- corporation of tyrosine and dopa predominated (15). From the hair of this species we were able to isolate a trichosiderin-like indicator pigment. Drugs and aging also may bring about red-black conversions these have been discussed in previous publications (2, 15). CONCLUSIONS The red pigmentary system is widely distributed in nature. So far we isolated indicator-like red pigments ("siderins") from seven species: man, dog, rabbit, hamster, rat, mouse, and chicken. As they provide a biologically less advanced method of protection against ultraviolet ir- radiation, red pigments may be phylogenetically older than black melanins. The interconversion between red and black pigmentary path- ways lends support to such an evolutionary hypothesis. ACKNOWLEDGMENT The author is •eatly indebted to Dr. Miklos Bodanszky, Case Western Reserve University, for amino acid analyses and chemical advice. (Received May 21, 19139) REFERENCES (1) Flesch, P., Esoda, E. J., and Katz, S., The iron pigment o[ red hair and feathers, .J. Invest. Dermatol., 47, 595-7 (1967). (2) Flesch, P., The epidermal iron pigments of red species, Ibid., 51, 337-43 (1968). (3) Prota, G., Scherillo, G., and Nicolaus, R. A., On the structure of "trichosiderins," Rend. •tccad. Sci. Fis. Mat. (Soc. Naz. Sci., Napoli) , 85, 14 (May, 1968). (4) Boldt, P., and Hermstedt, E., Pyrrotrichole, eine Gruppe [arbiger Verbindungen aus rotem Menschenhaar, Z. Naturforsch., 22b, 718-22 (1964). (5) Boldt, J., zur Kenntnis des Trichosiderins, eines Pigments aus roten Haaren, Naturwissenschaften, 51,265 (1964). (6) Prota, G., and Nicolaus, R. A., Struttufa e biogenesi delle feomelanine. Nora I. Isolamento e propriet'h dei pigmenti delle plume, Gazz. Chim. Ital., 97, 665-84 (1967). (7) Prota, G., Scherillo, G., Napolano, E., and Nicolaus, R. A., Struttufa e biogenesi delle feomelanin.e. Nora II. Sulla reazione tra o. chinoni e cisteina, Ibid., 97, 1451-78 (1967).