JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS was presumed to have had such an effect upon such enzymes in the skin culture. Tissue-culture studies on adult human skin, consisting of epidermis and a thin layer of dermis removed from the flexor surface of the forearm, have been made in relation to allergens and the toxic effects of antibiotics (Pomerat et alia, 1952 and 1953). Outgrowth of the epithelium, which appeared 'in two to three days after culture and reached a maximum in about six days, was used as a measure of continued activity of the tissue. A moderately close correlation was observed between the in vitro effects of antibiotics in restrict- ing outgrowth and their in vivo effects when applied to intact skin and mucous membranes. A comparison of the behaviour of cultures of adult human forearm skin with the skin of healing wounds in rats has been carried out by Washburn (1954) using histochemical procedures to reveal glycogen distribution and the distribution of ribo- and deoxyribonucleic acids. Glycogen is the form in which an animal normally stores carbohydrate, and can provide a source of energy for the activities of the tissues. In many tissues, the amount of ribonucleic acid increases w/th increase in protein synthesis. Deoxy- ribonucleic acid is specifically associated with the cell nucleus. In the normal human skin there is only a small amount of detectable glycogen in the epidermis, but when the cells from the surrounding epidermis and from hair follicle residues migrate over the surface of a healing skin wound, all the layers of the migrating epithelium, except the basal layer, in which the cells are actively dividing, contain glycogen. The glycogen disappears when keratinisation of the cells forming the epithelium of the wound takes place. In culture, the cells of the human skin which contained large amounts of glycogen were those which migrated and proliferated. Thus, a similarity between the metabolic processes involving carbohydrate in wound healing and in culture was suggested. In both wound-healing and skin-culture it was found that the content of ribonucleic acid remained unchanged during initial migration, but when proliferation occurred an increase in the content of this nucleic acid took place. There was no diminution of the deoxyribonucleic acid content of the culture during its activity. The interpretation of the results obtained in tissue culture studies in re- lation to the behaviour of that tissue in vivo must be treated with caution due to the need of materials such. as chick embryo extract and fowl plasma extract, for example, in the media. However, it should be noted that the constituents of the culture media are frequently obtained from animals of an entirely different class from those whose tissues are studied, yet normal development proceeded in the tissue with no indication of reaction against the foreign plasma proteins. Medawar was successful in maintaining his skin slices for four days without serum in the medium and survival was demonstrated by grafting. The extension of the use of tissue culture methods for toxicity 122

THE SKIN AS A COMMUNITY OF STRUCTURES and other pharmacological studies indicates a r.esponse characteristic of the skin itself rather than of the intact animal (Pomerat & Leake, 1954 Livingood & Hu, 1954). In addition to culture of the epidermis and part of the dermis without further disintegration, studies have been made on portions of skin during investigation of vesicants (Dixon & Needham, 1946). However, these studies were concerned with the presence or absence of certain enzymes after treat- ment of the skin on the intact animal and were not continued for periods of time comparable with those used in tissue culture methods. A recent report of studies of a skin homogenate, prepared by disintegration of the tissue by grinding (Griesemer & Gould, 1954), provides evidence of the ability of certain enzyme systems to function satisfactorily six to seven hours after preparation of the homogenate. Materials related to' carbohydrate meta- bolism were added to the homogenate and the rate of respiration was measured. The results, however, did not allow of any precise conclusions on the path of carbohydrate metabolism in the epidermis. In relation to the processes characteristic of the skin itself, the following tentative conclusions may be drawn from the studies discussed above. Maximum production of keratin takes place when the skin and its structures are provided with a vascular system, but the production of hair and keratin- ised epidermis can still take place independently of the intact animal. The process of utilisation of carbohydrate in the active migration and differentia- tion of epithelial cells and the incorporation of only very small amounts of sulphur from sulphate during keratinisation are normal. The changes in ribonucleic acid content of the cells are consistent with increased protein synthesis. The emphasis has fallen inevitably upon the process of keratinisation because it has received the greatest amount of study. Its relation to pigment production and the activity of the sebaceous glands will form much of the subject matter of the second and third parts of this paper. REFERENCES Dixon & Needham, 1946, Nature (London), Sept. 28, 158, 432. Fell, Mellanby &Pelc, 1954, British Medical Journal, Sept. 11,611. Griesemer & Gould, 1954, Journal of Investigative Dermatology, 22, 299. Hardy, 1949, Journal of Anatomy, 83, 364. 1951, Annals of the New York Academy of Sciences, 53, 546. Hardy, Biggers & Claringbold, 1953, Nature (London), Dec. 26, 172, 1196. Kahn, 1954, ibid., Aug. 14, 174, 317. Livingood & Hu, 1954, Annals of the New York Academy of Sciences, 58, 1202. Medawar, 1947, Quarterly Journal of Microscopical Science, 88, 27. 1948, ibid., 89, 187. Pomerat et alia, 1952, Journal of Investigative Dermatology, 18, 193. 1953, ibid., 20, 357. Pomerat & Leake, 1954, Annals of the New York Academy of Sciences, 58, 1110. Washburn, 1954, Journal of Investigative Dermatology, 23, 97 and 169. 123