THE QUANTITATIVE DIFFERENTIATION 349

350 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 5. The residual fat was once more photometrically estimated. 6. Fat free cigarette paper was affixed to the forehead for 3 hrs., and the fat estimated as described by Strauss and Pochi (10), bearing in mind the findings of Cunliffe and Shuster (11). 7. The residual fat was photometrically estimated. 8. Finally, the regeneration of lipids was photometrically estimated 3 hrs. later. The sebum excretion over 3 hrs. was also measured, first photometrically, then gravimetrically and once more photometrically. The following is a synopsis of the results: a) The initial photometric estimation always yielded higher results than the third measurements, which was carried out after the cigarette paper test. This indicates that the regeneration of the skin surface lipids is influenced by removal of the sebum by the cigarette paper. b) The photometric method always yielded lower values (in/ag/cm") than the gravimetric ones. c) In both the gravimetric and the photometric estimation there is excellent agreement between right and left values. d) These methods are not directly comparable one patient group exhibited high values with both the gravimetric and photometric method, whereas another group showed relatively high values with the gravi- metric estimation only. A third group displayed low values with both methods, although the gravimetric method, yielded slight higher values. These results underline the differentiation between these two methods, outlined in the introduction. In each case different parameters are being measured. The measurement of Strauss and Pochi, as will be discussed later, estimates the amount of sebum, which can be obtained from the follicle under the experimental conditions. The glass slide method, on the other hand, measures the lipid layer spread on the skin surface. The regeneration of this film is apparently slowed by the preceding capillary suction of the cigarette paper and the resultant extraction of sebum from the follicle. DISCUSSION As mentioned in the introduction, the different methods employed for skin lipid measurements, are based on different parameters. Thus, solvents elute lipids not only from the surface layer but also from the horny layer and upper part of the follicle. Correspondingly, the resulting values represent lipid from the surface together with that from deeper layers. This latter is