472 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS A final point to be made in these studies is the very small amount of cysteine lost, less than 0.05 meq, when either reduced or untreated hair is hydrolyzed in acid in the presence or absence of added cysteine. In the absence of hair, cysteine can be recovered from the hydrolysis and titration procedure in quantitative amounts. In the presence of hair, however, the very small amount, 0.05 meq, is lost. The reason for this loss is not •vell understood but the magnitude of the loss clearly does not interfere xvith the utility of the procedure. CONCLUSIONS A method has been developed for the quantitative differentiation of CySSO,q- and CySH residues in chemically treated keratin. The procedure was validated by verifying the assumptions on which it is based and showing that keratin, in this ease human hair, containing predictable CySSOa- to CySH ratios gave analytical results consistent with expectations. The method was shown to be applicable to analyzing keratin treated under a variety of conditions including acidic and alkaline bisulfite. The method was also shown to be useful on hair containing a wide range of CySSOa- to CySH ratios as xvell as hair containing only CySSOa- or CvSH groups. (Received January 31, 1974) REFERENCES (1) Elsworth, F. F. and Phillips, H., The examination of "sulfur stored" and "sulfited'" wool fabrics for sulfur dioxide and sulfite, J. Tex. Inst., 29, T219 (1938). (9.) Stein, H. H., an•d Guarnaccio, J., The determination of sulfhydryl groups in reduced hair keratin, Anal. Chim. Acta, 23, 89 (1960). (3) Leach, S. J., The reaction of thiol and disulfide groups with mereuric chloride and methylmercuric iodide. I. Simple thiols and soluble proteins, Aust. J. Chem., 13, 520 (1960). (4) Valk, G., and Gerthsen, T., A possible method for determination of groups of colored salts attached to wool, Melliand Texti•ber., 47, 407 (1966). (5) Klotz, I. M., and Carver, B. B., A spectrophotometric titration for the determination of suli•hydryl groups, Arch. Biochem. Bioph•!s., 95, 540 (1961). (6) Wolfram, L. J., private communication, 196•. (7) Menkart, J., and Wolfram, L. J., U.S. Patent 3,•67,363 (March 2, 1971). (8) Wolfram, L. J., and Underwood, D. L., The equilibrium between the disu]fide linkage in hair keratin and sulfite or mereaptan, Text. Res. l., 36, 947 (19Ff).

]. Soc. Cosmet. Chem., 25, 473-479 (September 19741 Testing Antiacne Agents in Mexican Hairless Dogs J. J. LOUX, M.S.,* P. D. DePALMA, B.S.,P and S. L. YANKELL, Ph.D.p Synopsis-The plugged follicles on the backs and flanks of MEXICAN HAIRLESS DOGS share clinical and histologic similarities to the comeclones seen in man. SOAP treatments cleaned follicle-containing areas but did not remove the follicular plugs. SALICYLIC ACID preparations were similarly ineffective. The use of BENZOYL PEROXIDE pro- duced slight extrusion of the follicular keratin plus mild irritation, and VITAMIN A ACID was markedly effective with associated dermal irritation. INTRODUCTION Several authors have reviewed the literature for information relating animal and clinical skin research (1, 2). A symposium presented at the 52nd annual meeting of the Federation of American Societies for Experimental Biology discussed the choice of animal models for the study of disease processes in man (3). Although there are many mammalian and avian models for clinical skin diseases, no references were cited in the above papers on any form of spontaneous animal acne. Currently, laboratory evaluations of acne treatments rely on chemically in- duced comedones in the ears of rabbits. The hyperkeratinization is similar to that causing follicular hyperkeratosis in occupational chloracne (4). Human sebum lipids (5) and fatty acids (6, 7) which have relevance to the etio- pathogenesis of acne also have been employed as acnegens in the rabbit. Van Scott reported at the 1970 symposium on the Biology of the Skin that the rhino mouse was a natural model of keratin invagination (8). By studying the skin histology of this animal in relation to the animal's age, a reproducible method for measuring progressive cyst formation was developed. Experimen- tal materials used to treat clinical acne were applied to the skin to test their efficacy in preventing or alleviating this keratin invagination. Sulfur and resor- cinol had no activity however, retinoic acid proved very effective. *Present address: 110 E. Hanover Ave., Cedar Knolls, N.J. 07927. ?Menley & James Laboratories, 1500 Spring Garden St., Philadelphia, Pa. 19101. Reprint requests should be addressed to Dr. Yankell. 473