KERATIN REPLACEMENT AS AN AGING PARAMETER 547 are needed to determine if the average individual growth declines in a linear, stepwise, or other fashion. Preliminary studies performed on dogs (Fig. 11) show that young and middle aged dogs' claws grow about 1.3 mm a week, whereas old dogs average 0.8 mm a week (18). Techniques described by Godwin (15) for measuring nail growth in the rat may permit controlled aging studies on this animal. Further experiments on factors which affect nail growth, the relation- ship of linear growth to nail volume, and the linearity of longitudinal measurements over extended periods of time will reveal more informa- tion as to the true meaning of this measurement. To date, the use of linear nail growth measurements as a parameter of physiologic age appears both 'valid and significant. (Received November 14, 1966) (1) (2) (3) (4) (5) (6) (7) (8) (9) (lO) (11) (12) (•3) (14) (15) (16) (17) (18) REFERENCES du Nouy, P. leComte, Biological Time, The Macmillan Co., New York, 1937, pp. 51-101. Strehler, B. S., Time, Cells, and Aging, Academic Press, New York, 19f•2, p. 96. Epstein, W. L., and Maibach, H. I., Cell renewal in human epidermis, Arch. Dermatol., 92,462 (1965). Katzberg, A. A., Influence of age on rate of desquamation of the human epidermis, Anat. Record, 112,418 (1952). Thuringcr, J. M., and Katzbcrg, A. A., The effect of age on mitosis in the human epi- dermis, J. Invest. Dermatol., 33, 35 (1959). Van Scott, E. J., Ekel, J. M., and Auerbach, R., Determinants of rate and kinetics of cell division in scalp hair, Ibid., 41,269 (1963). Weinstein, G. D., and Van Scott, E. J., Autoradiographic analysis of turnover times of normal and psoriatic epidermis, Ibid., 45,257 (1965). Barman, J. M., Pecoraro, V., and Astore, I., Method, technic and computations in the study of the trophic state of the human scalp hair, Ibid., 42,421 (1964). Barman, J. M., Astore, I., and Pecoraro, V., The normal trichogram of the adult, Ibid., 44, 233 (1965). Rook, A., Normal and abnormal hair growth in old age, Gerontol. Clin., 7, 8 (1965). Babcock, M. J., Methods for measuring fingernail growth rates in nutritional studies, J. Nutrition, 55,323 (1955). Bean, W. B., Nail growth, Arch. Internal Med., 11,476 (1963). Bean, W. B., A discourse on nail growth and unusual fingernails, Am. Clin. and Climat. Assoc., 74, 152 (1963). Geoghegan, B., Robcrts, D. F., and Sampford, M. R., A possible climatic effect on nail growth, Appl. Physiol., 13, 135 (1958). Godwin, K. O., Experimental study of nail growth, J. Nutrition, 69, 121 (1959). Hamilton, J. B., Terada, H., and Mestler, G. E., Studies of growth throughout the life- span in japanese: growth and size of nails and their relationship to age, sex, heredity, and other factors, J. Gerontol., 10, 401 (1955). Hillman, R. W., Fingernail growth in the human subject, Human Biol., 27,274 (1955). Orentreich, N., and Ettinger, S., Unpublished data.

548 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Society of Cosmetic Chemists • 967 Meetings The Society of Cosmetic Chemists will hold the following meetings in 1967: Date Meeting Location Sept. 21, 1967 Sept. 22, 1967 Dec. 6, 1967 Seminar Semi-annual Ambassador Hotel Chicago, Illinois Americana Hotel New York, New York