HAIR AND WOOL 78,5 Data for the moisture regain, determined under desorption conditions at 65% R.H. and under absorption conditions at 87% R.H., are given in Table VII. Only slight differences among the various fibers are seen. 4. Mechanical Properties--The data of Table VIII were obtained in single cycle force-extension tests to break on an Instron tensile tester, 2.54 cm fiber specimens being extended at 2.54 cm/min, the broken fibers being subsequently weighed on a torsion microbalance to establish their linear density. (As noted in Section III, A, 2, the Negro hair fibers are a different material from that used in the rest of the study.) The two hair samples behave very similarly the wool is stronger and more extensible--a finding in direct contrast to that in Table I. This strikingly illustrates the variability resulting from differences between samples and test procedures. 5. Diffusion of Reagents--Diffusion appears to be the rate-deter- mining step in the reduction of keratin by mercaptans (46) and by sul- rites (47). Thus, the rate of reduction may be used to compare the diffusion of the reagents in different fibers. The results of such measurements at 36 øC, using ammonium thio- glycolate at pH 9.3 and ammonium sulfite at pH 6.0, are given in Figs. 10 and 11. The two types of hair give practically identical curves, except for the slightly lower reduction level of Caucasian hair in the later stages of the reaction with thioglycolate the wool is reduced much more rapidly. When the data are considered in terms of the fraction of the disulfide bonds ruptured, the equilibrium is found to be somewhat higher for wool in the case of thioglycolate (Fig. 12) and identical for all three fibers in the sulfite experiment. 6. Rates of Reaction--The solubilities of the three fibers in the urea- bisulfite and the alkali tests are recorded in Table IX. As expected, the hair is more resistant to attack than wool in both media. In the UB test, a difference between the two hair types appears, the reasons for which are not clear. When the cystinc and cysteine contents of the residues from the tests were determined by the Zahn-Traumann method (45), the two hairs again behaved very similarly to each other and differently from the wool (Table X). The response to boiling dilute acid was measured by determining the weight change (a) in the acid exposure itself and (b) in subsequent alkali solubility test. The results, which are summarized in Table XI, again show a large difference between the hair and wool, with the two hair samples quite closely matched.

786 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS IV. CONCLUSIONS A comparison of the morphological structure, chemical composition, diffusion of reagents, rate of reaction with various agents, and setting and supercontraction behavior reveals some significant differences between wool and hair the two hair types, Caucasian and Negro, ap- pear very similar in all the features examined. In acid binding and moisture regain, all the fibers are similar. The fiber mechanical properties exhibit considerable variations even within a fiber type. The slower rate of diffusion of reagents into hair and its greater re- sistance to chemical modification are due to structural differences at both the morphological and molecular level specifically, the important factors are the thicker cuticle and the more extensive covalent cross- linking of the hair keratin. ACKNOWLEDGMENT This study forms part of the basic research program of The Toni Co. (Received April 22, 1966) REFERENCES (1) Speakman, J. B., and Coke, C. E., J. Soc. Dyers Col., 54, 563 (1938). (2) Danforth, C. H., Nat. History, 26, 75 (1926) idem., Physiological Rev., 19, 94 (1939). (3) Kolar, G. G. and Parker, P., Chapter 25 in Sagarin, E., Cosmetics, Science and Tech- nology, Interscience, New York, 1957. (4) Steggerda, M., and Seibert, H. C., J. Heredity, 32, 315 (1941). (5) Trotter, M., Am..[. Phys. Anthrop., 14,433 (1930). (6) Rudall, K. M., Proc. Leeds. Phil. Soc., 4, Part I, 13 (1941). (7) Speakman, J. B., and Smith, S. G., J. Soc. Dyers Col., 52, 121 (1936). (8) Speakman, J. B., J. Soc. Chem. Ind., 50, 1 (1931). (9) Mercer, E. H., Text. Res..[., 23,388 (1953). (10) Dusenbury, J. H., and Menkart, J., Proc. Intl. Wool Text. Res. Conf., 1955, F142 Dusenbury, J. H., and Jeffries, E. B., J. Soc. Cosmetic Chemists, 6, 355 (1955). (11) Mercer, E. H., Text. Res..[., 24, 39 (1954). (12) Fraser, R. D. B., and Rogers, G. E., Austr..[. Biol. Sci., 8,288 (1955) Fraser, R. D. B., and MacRae, T. P., Text. Res..[., 26, 618 (1956). (13) Menkart, J., and Coe, A. B., Text. Res..[., 28, 218 (1958). (14) Rogers, G. E., Ann. N.Y. Acad. Sci., 83,378 (1959) Fraser, R. D. B., MacRae, T. P.. and Rogers, G. E., Nature, 183, 592 (1959) idem., .[. Text. Inst., 51, T497 (1960). (15) Geiger, W. B., Text. Res..[., 14, 82 (1944). (16) Bradbury, J. H., and Chapman, G. V., Austr..[. Biol. Sci., 4, 17 (1964). (17) Crewther, W. G., Fraser, R. D. B., Lennox, F. G., and Lindley, H., Adv. Protein Chem., 20, 191 (196,5). (18) Speakman, J. B. and Elliott, G. H., Symposium on Fibrous Proteins, 116 (Soc. Dyers Col., Leeds, 1946). (19) Speakman, J. B., Trans. Faraday Soc., 26, 92 (1929) J. Soc. Chem. Ind., 49, 209T (1930).