256 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS _ Figure 10. (1) Untreated guinea pig comeurn, 200 x, (2) guinea pig comeurn treated in 2:1 chloroform- methanol mixture, followed by extraction in distilled water, 200 x The effect on the water vapor sorption isotherm of treating guinea pig corneum in a 2:1 •'•' chloroform-methanol mixture, followed by extraction in distilled water, is shown in Fig. 7. Curve A depicts the water vapor sorption isotherm for intact (untreated) cor-' neum, and curve B depicts the effect of the organic solvents-water treatment. Similar results for this system have previously been reported by Singer and Vinson (4). It is • seen that the initial portions of the isotherms up to about 50 per cent RH almost coin- cide, but the two curves markedly diverge beyond 70 per cent RH. A total number of 4 water vapor sorption-desorption isotherms were obtained on different comeurn pieces from the same guinea pig sample, treated in the organic solvents and water. The repro- • ducibility of the data points on the isotherms was within 1 per cent of the mean. The substantial decrease in the water vapor sorptive capacity of the treated guinea pig cor-- neum in the higher humidity range indicates a marked change in the corneum structure which affects primarily the formation of multilayers. The extraction of some materials and, perhaps, disruption of molecular bonds could conceivably result in a more open

THE STRATUM CORNEUM 257 matrix structure and, hence, decrease the possibility of multilayer formation. It is also expected that the diffusion of water vapor molecules would be faster in such a modified structure. This is evidenced by the diffusion coefficient-concentration relationship, -- shown in Fig. 8 as the intrinsic diffusion coefficient Di and mean diffusion coefficient D against percentage water vapor uptake. An average increase of an order of magnitude in the value of D is observed as a result of the solvent treatment. Compare Fig. 9 which shows data for the untreated comeurn. The effect of treatment was also assessed with the help of SEM. Figure 10 (1) and (2) provide a comparison between intact (untreated) and treated guinea pig comeurn. The effects of the organic solvent treat- ment are quite apparent in (2), as judged by the extent of cleavage and disruption of the cellular matrix. "- REFERENCES .: (1) I. Blank, J. Invest. Dermatol., 18, 433 (1952). :: (2) B. Idson, J. Soc. Cosmet. Chem., 24, 197 (1973). . •:. (3) J. Mtddleton, Brit. J. Dermatol., 80, 437 (1968). .:•:• (4) E. Singer and L. Vinson, Proc. Sci. Sect. Toilet Goods Ass., 46, 29 (1966). (5) R. Wildnauer et al., "Applied Chemistry at Protein Interfaces," in Advances Jn Chemistry Series Number ß ::': 145, R. Baler, Ed., p. 74, 1975. (6) A. EI-Shimt and H. Princen, Water vapor sorption and desorption behavior of some keratins, ..:'' to appear in Colloid Polym. Sci. (7) A. EI-Shimi and H. Princen, Diffusion characteristics of water vapor in some keratins, to appear in Colloid Polym. Sci. ß :11. (8) R. Scheuplein and I. Blank, Phys•ol. Rev., 51,702 (1971). ' ::': (9) R. Tregear, Physical Functions of Skin, Academic Press, New York, 1966. .:::::• (10) G. King and A. Cassie, Trans. Faraday Sot., 36, 445 (1940). (11) I. Blanket al., J Invest. Dermatol., 49,582 (1967). (12) R. Scheuplein and L. Ross, J. Soc. Cosmet. Chem, 21,853 (1970). ., i'.':. (13) A. Kligman and E. Christophers, Arch. Dermatol., 88, 70 (1963). ".":.:• (14) A. EloShimi, H. Princen and D. Risi, "Applied Chemistry at Protein Interfaces," in Advances in Chemistry Series Number 145, R. Baler, Ed., p. 125, 1975. i: (15) A. E1-Shimi and E. D. Goddard, J. Colloid. Interfac. Sci., 48,241 (1974). :: .... (16) R. D'Arcy and I. Watt, Trans, Faraday Sot., 66, 1236 (1970). i: :' (17) B. Zimm, J. Chem. Phys., 21,934(1953). (18) J. Crank, Mathematics of Diffusion, Oxford University, England, 1950. ß ....