In a preliminary report evidence was presented to show that an alteration in the structure of a compound extractable from mouse epidermis with alcohol and ether occurs in the process of epider

The essentials of the extraction procedures and the polarographic method were described previously (3), and any variations from those already given are in the proper place. Polarograms of the lipids were made in a mixture of unbuffered or buffered solution, dioxane, and tetrabutylammonium iodide (0.1 M). This quaternary ammonium salt was employed as supporting electrolyte to reach potentials in the region of —92.92 to —92.4 volts versus the saturated calomel electrode (S.C.E.) at which potentials some of the lipid material is reducible (3). All potentials in this report are in volts vs. the S.C.E., hence no further reference to the latter is given. The epidermis of normal untreated mice and methyl cholanthrene-treated mice was removed by blunt dissec tion at 50° C. on a thermostatically controlled hot plate by the procedure of Baumberger, Suntzeff and Cowdry (1). By this method practically pure epidermis is easily separated from the dermis as verified by microscopic study of both isolated portions of tissue. Even when the epidermis is removed at room temperature by scraping there is little, if any, contamination with dermis (7). The ideal nature of epidermis for the study of car cinogenesis, and the advantages of this tissue for chemi cal analysis have been discussed by Cowdry (5). Methylcholanthrene-induced and three transplant able squamous cell carcinomas were used for this inves tigation. Some of the morphological characteristics of these tumors have appeared (3). In many instances transplantable tumors which were small, solid, and con taming little, if any, necrosis were used for lipid extrac tion, and the preparation and advantages of these have been described (8). When large methylcholanthrene induced or transplantable tumors were employed for analysis, the necrotic material was removed as thor oughly as possible with the aid of a magnifying lens. In