EXPERIMENTS ON EPIDERMIS OF ANIMALS 235 Linoleic acid was gently applied in the morning and in the evening to 22-day-old rats. On the following morning, skin was removed and placed on two diffusion chambers. The first hour the loss was 18.237 mg./sq. cm. By the 29th day of life, as shown by skin from animals of this age, the lino- leic acid was less effective and the loss was only 3.239 mg./sq. cm. Thus when the comeurn is dry, linoleic acid penetrates more rapidly. By this penetration the epidermis is altered and the water loss is tremendous. D•scuss•o2½ Hair growth, changes in the epidermis, fluid content, and metabolism of the skin are closely correlated in the rat. One may ask if we have condi- tions comparable to this in the human. Undoubtedly there are intervals when the metabolism of the human skin is low. The greater shedding of dry epidermal cells during the winter months is in all probability quite similar to the conditions in the low stage of the skin in the rat. When such a low exists, then applications of many substances may be irritative, resulting in parakeratosis and shedding of moist cellular material. If coolness does favor the formation of unsaturated acids (14), more of the latter may be found than usual during the winter months and enhance the shedding of epidermal cells. The fact that mineral oil caused parakeratosis and was not conducive to an improvement of the skin is somewhat disappointing for mineral oil is used widely in the cosmetic industry. According to O'Brien (15), daily applications of kerosene caused parakeratotic plugs in human sweat pores. The importance of a moist corneum has been emphasized in this review. One may ask if such a condition would not always be present in the human since the presence of sweat glands would supply much moisture to the surface while in the laboratory animals where the skin is devoid of sweat glands, this asset would be entirely lacking. Despite the presence of sweat glands and invisible perspiration in the human, I am still inclined to believe that the scalp and skin become very dry and need additional coverings to prevent water loss and thereby keep the corneum soft and moist. A moist comeurn, active granulosum, high fluid content, and high me- tabolism of the skin are characteristic of a good skin. In all these experi- ments, lanolin is the only substance which has not affected the skin ad- versely. Castor oil also seemed to have little effect. The other substances, in many instances, induced parakeratosis which was not due to the retarda- tion of desiccation for wool fat, would have had the same effect. Lanolin undoubtedly prevents the loss of moisture content from the skin. What one needs is something which when applied will not only do this but also increase the metabolism and fluid content of the skin as a whole without causing parakeratosis. The development of this substance is the challenge for the cosmetic chemist.

236 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS REFERENCES (1) Butcher, E. O., "The Hair Cycles in the Albino Rat," dnat. Rec., 61, 5 (1934). (2) Butcher, E. O., "The Oxygen Consumption of the Skin During the Hair Cycle in the White Rat," rim. 7. Physiol., 138, 408 (1943). (3) Butcher, E. O., and Grokoest, A. W., "The Influence of Tissue Fluid on Hair Growth," Growth, 5, 175 (1941). (4) Butcher, E. O., "The Effects of Applications of Various Substances on the Epidermis of the Rat," it. Invest. Derrnatol., 16, 85 (1951). (5) Periman, A., "The Effect of Certain Lubricating Agents and Coarse Foods Upon the Cornification of the Oral Mucosa of the White Rat," 7. Dent. Res., 29, 1 (1950). (6) Harry, R. G., "Skin Penetration," Brit. 7. DermatoL & Syphilol., 53, 65 (1941). (7) Eller, J. J., and Wolff, S., "Permeability and Absorption of the Skin," drch. Dermatol. & Syphilol., 40, 900 (1939). (8) Calvery, H. O., Draize, J. H., and Lang, E. P., "The Metabolism and Permeability of Normal Skin," Phys. Reviews, 26, 495 (1946). (9) Butcher, E. O., "The Penetration of Fat and Fatty Acids Into the Skin of the Rat," 7. Invest. Dermatol., 21, 43 (1953). (10) MacKee, G. M., Sulzberger, M. B., Hermann, F., and Baker, R. L., "Histological Stud- ies on Percutaneous Penetration with Special Reference to the Effect of Vehicles," Ibid., 6, 43 (1945). (11) Johnston, G. W., and Lee, C. O., "A Radioactive Method of Testing Absorption from Ointment Bases," 7. rim. Pharm. dssoc., 32, 278 (1943). (12) Butcher, E. O., "Penetration of Radioactive Stearic Acid Into the Skin of the Rat," 7. Invest. DermatoL, 21, 243 (1953). (13) Burch, G. E., and Winsor, T., "Diffusion of Water Through Dead Plantar, Palmar, and Torsal Human Skin and Through the Nails," drch. Dermatol. & Syphilol., 53, 39 (1944). (14) Ralston, A. W., "Fatty Acids and Their Derivatives," New York, John Wiley & Sons, Inc. (1948), p. 78. (15) O'Brien, J.P., "The Effect of Lipoid Solvents on the Pores of the Skin," it. Invest. Der- matol., 15, 141 (1950). THE USE OF THE PENETROMETER IN THE DETERMINATION OF CONSISTENCY OF PETROLEUM JELLY* By R. T. DOBSON Chesebrough Manufacturing Co., Ltd., London, England THE OBJECT of this short talk is to explain to those not familiar with the penetrometer the working method to be employed with this apparatus and precautions which should be undertaken to ensure that repeatable and comparable results may be obtained which are indicative of differences in consistency between petroleum jellies from different sources. As many of you will be aware, the consistency of petroleum jelly can vary sufficiently to cause subtle differences in the finished product in which it is used and, although a Yellow B.P. W/A Grade 45 or a White B.P. W/A Grade 40A or 40B may be specified, you may not always receive supplies derived from * Presented at the April 9, 1954, Meeting, London, England.