WATER HOLDING CAPACITY OF CALLUS 277 from the epidermal or subepidermal tissue, only to lose it to the dry atmos- phere. Furthermore, if the ratio of glycerol to callus is lowered to more practical ratios, the hygroscopic qualities of glycerol are no longer dem- onstrable (cf. Table 9). In our work, we extracted from 15 to 18 per cent of solids from pulverized callus, depending on the method of extraction and the lot of callus. This value is in good agreement with the amount of water-soluble components extracted by Matoltsy and Balsamo (35), who showed that the amount of water extractables can vary from 12 to 21 per cent within the pH range of 5.9 to 8.2 and that the amount extracted depends on the time of agitation. Blank (3) has reported that the water absorption at 90 per cent R.H of washed whole callus--after removing 3.6 per cent and 7.2 per cent water- solubles--is approximately equal to the amount of water absorbed by un- washed whole callus. Our results with one of the lots of pulverized callus are in agreement with Blank's data, and, furthermore, we show (Fig. 3) about the same amount of water pickup after removal of 18 per cent water- solubles from callus. However, with a different lot of callus water washing decreased its water-holding capacity at 90 per cent R.H. by 13 per cent. Blank (3) also reported that pretreatment of callus with pyridine followed by extraction with water reduces its water-holding capacity from about 38 per cent to 2 a, per cent at 90 per cent R.H. and from about 63 per cent to 35 per cent at 97 per cent R.H., and pretreatment with petroleum ether followed by water washing reduces the water-holding capacity from ap- proximately 35 per cent to 30 l•er cent at 90 per cent R.H. Flesch and Esoda (11) reported that extraction of pulverized callus with ether followed by water reduces its water-holding capacity from 28 per cent to 18 per cent at 100 per cent R.H. Our findings show that washing with polar solvents (ether and ethyl alcohol) has little effect over washing with water alone on the water-holding capacity of the callus. Furthermore, a saml•le of water- washed pulverized callus (Lot #5 ww), from which approximately 18 per cent water solubles had been extracted, gave only an additional 2 per cent of water solubles after washing with pyridine, and the callus, so treated, again absorbed the same quantity of water as untreated pulverized callus (Lot #5 ww). Spier and Pascher (5) have found as much as 16 per cent oflactates in the water extractable solids of stratum corneum. The callus samples used in our work contained very little lactate. In view of the high hygroscopicity of sodium lactate, it is probable that the past history of the callus sample or stratum corneum used may account for some of the observed discrepancies. Callus derived from a subject who bathes or showers daily probably con- tains less of the water-soluble components than that obtained from less frequent bathers. Similarly, plantar callus is older and has been washed more frequently than scales obtained by scraping or stripping. These

:278 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS factors could well account for variations of moisture sorption reported for different lots of unwashed and washed callus. Our results single out sodium lactate, which is a natural constituent of epidermal tissue, as a most efficient humectant. The hygroscopicity of sodium lactate is demonstrable when one part of this material is mixed with nine parts of callus. Glycerol, however, when present in a low ratio, loses its hygroscopicity. While many of the water-soluble constituents in the stratum corneum are derived from the breakdown of living cells in the keratinization process, it should not be overlooked that many of these components, especially lactic acid, are supplied by sweat (40). Is it coin- cidental then that the skin is softest in warm weather when sweating pro- duces a high concentration of lactates on the skin and that it is driest during cold weather, when there is very little sweating and the lactate con- centration is low? In view of these findings and considerations, the authors would like to suggest that ]actares are important skin components responsible for the skin's water-holding capacity. IV. Summary and Conclusions 1. The effect of particle size and grinding on the moisture sorption of callus has been studied. 2. The moisture sorption of mixtures of relatively large quantities of glycerol, propylene glycol or crystalline sorbitol with callus has been studied at equilibrium. It has been shown that the total water absorbed is strictly an additive function. 3. The moisture sorption of washed and unwashed pulverized callus has been studied in constant humidity atmospheres, varying from 45 per cent R.H. to 90 per cent R.H. Widely different results were obtained with dif- ferent lots of callus. The history of the callus sample prior to work-up in the laboratory, however, may have an important bearing on these results. 4. The water sorption properties of equivalents of the major com- ponents in the water-soluble callus extracts have been measured indi- vidually. Among these, sodium lactate has more affinity for water than any of the other naturally occurring substances tested. 5. Glycerol, added to callus in small quantities, shows no hygroscopic effect. However, sodium lactate at low concentration enhances the water uptake of callus considerably. Atcknow/edgment: The authors wish to express their gratitude to Mr. J. Skillman for technical assistance in preparing graphs, etc. (Received May 8, 1962) References (1) Jacobi, O., Kol/oid-Z., 114, 88 (1949). (2) Blank, I. H., )t. Invest. DermatoL, 18, 433 (1952).