254 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS described above. After the applied dose had dried, the external skin surface was cleansed with water and cotton swabs. All cleansing materials were placed into scintillation vials containing 10 ml of scintillation fluid (New England Nuclear, Biofluor Scintillation Fluid). Following the cleansing, the dosed area was tape-stripped twenty times with the surgical tape. The tape strips were placed in scintillation vials containing 10 rnl of scintillation fluid and radioactivity determined by counting on a scintillation counter Figure 2. Photomicrograph of biopsy of human skin graft following exposure to aqueous solution of •4C-labeled alanine for two hours, then cryostated to 6 !xm thickness and autoradiographed.

HUMAN SKIN GRAFTED NUDE MOUSE 255 (Beckman, Model LS7500, Microprocessor Controlled). Two strips were combined per vial. These experiments were conducted using some of the main ingredients of the natural moisturizing factor to measure the effect of cosmetic bases on stratum corneum uptake. Determination of the uptake and penetration of test materials at different time intervals was conducted using para-aminobenzoic acid as a model agent. Those experiments were performed in much the same manner as described above, i.e. solutions of radiolabeled test substances were applied to premarked areas of skin. At various time intervals (1, 2, 4, and 8 hours) the areas were cleansed and all cleansing materials retained for counting. Twenty tape-strippings were taken on each area and the tape strips placed into scintillation vials containing scintillation fluid and counted on a scintillation counter. As in the test to determine efficiency of the method, the first strip was counted separately, while the remaining strips were combined two per vial. RESULTS AND DISCUSSION In Figure 1 the human skin transplanted athymic nude mouse is shown. This model is believed to approximate the conditions of human skin better than any of the models currently being studied, although further studies are needed (18). This paper was de- signed primarily to describe the practicality of testing procedures and to assess the athymic nude mouse as a useful model in cosmetic research. The data presented in this paper are the preliminary results of ongoing research carried out with NMF and other agents. 30 20 10 I I I I 10 15 20 25 I i 0 5 30 number of strippings Figure 3. Rate of removal of stratum corneum of the human skin transplant determined by weighing strippings. From the tenth stripping onwards the strips do not remove as many layers. This may be dependent on the thickness of the stratum corneum.