PHOREOGRAPHY 9 RESULTS We want to present two sets of experiments. The first experiments were carried out to determine if the living cells of epidermis are responsible for non-linear phenomena. The second experiments were to evaluate the damage caused by uv radiation. Living structures involved in phoreographical responses The first step was to confirm that non-linearity is due to living struc- tures. The in vitro measurements constitute a very convenient way to check this point as one can easily change the various parameters and create well- defined situations. The following experimental results were obtained: (1) If the skin is irrigated by a proper medium, it is possible to obtain phoreographical responses for 6 or 7 h providing this medium is correctly and permanently oxygenated. (2) The non-linear phenomena disappear very quickly if potassium cyanide or dinitrophenol is added to the perfusion medium. (3) There is a relation between the observance of non-linearity and transcutaneous potential. As a rule both vanish at the same time and seem to originate from the same structures. Besides these data obtained by in vitro measurements, phoreographical determinations have been made on whole animals showing that: Non linearity disappears after killing the animal. The threshold value can be modified by anaesthesia. It seems to be a relation between the threshold value and the age of the animal, the older it is the higher is the threshold value. Phoreographical response disappears when animals are on a lipid- deficient diet. All these results show without any doubt that living structures are responsible for non-linear response. Conversely, since the rat is a sweat gland deficient animal and since in vitro preparations contain no living struc- tures but cells of epidermis and follicles, it seems obvious that such a response originates from either or both. However, it is possible to obtain the same response on human beings, on parts of the body deprived of any hair, so it seems to be a reasonable assumption to attribute the response to the living cells of epidermis. As far as the rat is concerned, the phoreographical reponse is very

l0 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS probably a one component response. On human beings the non-linear phenomena are more complicated due to the presence of sweat glands. It is not possible by cathodic stimulation to distinguish between glands and purely epidermal cells but by applying anodic stimulations one can generally obtain a response, the usual pattern of which is shown in Fig. 5. Time (Icm/20 4 3 2 ! Figure $. Skinrespone to ananodic stimulation 0,5 I 1.5 One can see that the diagram is S-shaped, an increase of skin resistance following the previous disease. We cannot say in the present state of our experiments whether or not two kinds of living structure, i.e. epidermal cells and sweat glands are responsible for this particular aspect of the response. It must be kept in mind that Edelberg (2), using minute electrodes, showed that polarization of epidermal cells and sweat glands occur in opposite sense. If it is the case, anodic stimulation would be very useful to assess separately the physiological conditions of these two structures. Phoreograoehical determination of uv damage It is well known that erythema evaluation is a critical problem for deter- mining uv damage. Furthermore, rats do not present erythema at all and