142 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Rapid initial dehydration was followed by much smaller changes until equilibrium was reached. The dehydration is a function of the relative humidity of the laboratory atmosphere and of air circulation. The rate of dehydration was quite uniform for the individual callus pieces. There was no overlapping of the s,orption and desorption curves, an effect well known as hysteresis. Organic Solvents The action of organic solvents on callus has been reported previously (7, 9). We repeated some of the earlier work besides the fact that such experiments are valuable in providing figures for lipids and other ex- tractibles, we wanted to compare results of earlier workers with our own. Blank (7) and Middleton (9) reported that the composition and amount of human epidermal lipids is significant for the retention o[ water by the stratum comeurn and, hence, the softness of the skin. The composition of skin surface lipids shows considerable variations both in different areas of the body of the same individual and in the same area of the body of different individuals (10). The lipid content of the epi- dermis of the human sole was found ,to be consistently lower than the lipid content of the epidermis from other regions (11). The lipid com- position of the epidermis also changes during the process of keratiniza- tion (12). The phospholipid and cholesterol contents of the cells of the epidermis decrease greatly during keratinization. It can thus be ex- pected in our experiments with surfactants and humectants that the water-binding capacity of callus will reflect more the properties of kera- tinous materials than the properties of skin lipids. Blank (7), and later Mi,ddleton (9), found that extraction of callus with an organic solvent, followed by water, extracted much more sub- stance from the callus than extraction by either water alone or water followed by organic solvent. We were not successful in duplicating Table I Solvent Extraction of Callus Pieces Weight Loss • Extraction Sequence (%) Water-acetone-water-acetone Water-alcohol-water-alcohol Water-pyridine-water-acetone Water-alcohol-chloroform-alcohol 10.7 17.0 12.5 15.4 • Of experimental in excess of weight loss of water-extracted control.

ABSORPTION OF CHEMICALS ON SKIN Blank's results however, we extracted up to 17% material from callus with various organic solvents when the callus was previously swollen in water. Table I indicates the solvent systems used and the weight losses obtained. These experiments indicate that other materials besides lipids are extracted from callus with organic solvents and the assistance of water. Extraction of Water-Soluble Substances from Callus by Surfactants The following surfactants were examined: sodium lauryl sulfate, sodium lauroyl isethionate, polyoxyethylene sorbitan monostearate (Tween 80),* cocoyl sarcosine, and sulfated ethoxylated fatty alcohol. Sodium lauryl sulfate and sodium lauroyl isethionate were chosen to allow direct comparison with the results obtained by Middleton (15) who worked with guinea pigs' footpads. He found a somewhat greater extraction of water-soluble substances by the use of sodium lauryl sulfate than by the use of sodium lauroyl isethionate: 9.5% versus 7.9%. We found increased extraction by isethionate this was more pronounced at higher concentrations (Fig. $). The immersion time for the various callus pieces was 24 hours, and the drying time was g days. Thus, different surfactants had different solubilizing capacities, and these became more evident at higher concentrations. At the lower sur- factant concentrations, there may have been an overlapping between *Atlas Chemical Industries, Inc., Wihningtou, Del. 19899. • +• o, _z o -- Lu •: -25 © SODIUM LAURYL SULFATE [] SODIUM LAUROYL ISETHIONATE 0.075 0.15 MOLAR CONCENTRATION Figure 3. Weight gain or loss after drying of experimental moieties of callus immersed 24 hours in surfactant solutions of different concentrations as compared to the weight loss of the control callus moiety immersed in water