332 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS RESULTS AND DISCUSSION Beef snout epidermis because of its availability and thickness is a good source of material for studies on the structural proteins of epidermis. This tissue has all the strata of epidermis well defined and it is covered with a thick coat of keratin (Fig. 1). At high magnification the tonofibrils be- tween adjacent squamous cells are well delineated (Fig. 2). Beef snout skin left in 6 M urea solution at 0 ø for one hour showed tonofibrils in many cells, particularly in the outer Malpighian stratum, whereas this tissue left ........ ..,.. %,, ':.a, ...... •.', '•,,•, '• ?:':.,.:i-$, ".'%.: ....... 4. ß %'• '•1 ' .. "?. '.'"' •-•= ½ 7 ...xz, ..? . . ......... 4. :.4. ':..:½•r:' •.:o•k•½•,.: •t•. ' - [igure 2.•Beef snout epidermis, Malpighian layer, X 450. •ote the tono•bdls between adjacent cells. --•. -, .:•.• :• '-• •- • •. •v:'? .... 7•...• ....... ..• : '% • ..... . 4 •'• "• ..... .:•_ . .... • %... . .... .. ,, .•. .•... • .... • •. .... -• •--• '-L.- .2 ?' • • :•ø-:.. :."' -.-s-•- '•i:, ........ ' "_ . .., . . Figure &--Beef snout epidermis, X 450 which had been in a 6 M urea solution for St/,. hours at 0øC. Note empty spaces between some of the cells and pycnotic nuclei.

PROTEINS OF EPIDERMIS, RELATION TO AGING SKIN 333 for five and one-half hours at 0øC. showed most of the cells surrounded by empty spaces with but traces of tonofibrils in the same region (Fig. 3). The remainder of the epidermis appeared to stain quite well and showed most of the normal features of this tissue. Beef snout skin left in 6 M urea solu- tion at room temperature for twenty-four hours showed numerous signifi- cant alterations in structure. The epidermis was somewhat thinner and the cytoplasm less granular than the normal untreated skin, and the nuclei appeared pycnotic (Fig. 4). The granular layer was present and the kera- Figure 4.--Beef snout epidermis, X 100, which had been in a 6 M urea solution for 24 hours at room temperature. Note the separation of the epidermis from the dermis due to solution of cellular materials from the lower strata. Keratin layer intact. tohyalin granules, assumed sites of conversion of the true keratin from the keratin precursors (26), stained well and the coat of keratin was intact (Fig. 5). Tonofibrils were absent, but empty spaces between the cells were present and many cells were free in clumps as though a cement-like sub- stance had been dissolved. Beef snout skin left in a 6 M urea solution for ninety-six hours had only traces of epidermis remaining intact solution of a large portion of this tissue in the lower strata resulted in the upper layers of the epidermis being cast off. The dermis appeared not to have dissolved to any appreciable extent. It would appear then that a 6 M urea solution extracts from epidermis, among other substances, the materials composing the tonofibrils, but microscopically appears to have no appreciable solubil- izing effect upon the keratin covering or upon the keratohyalin granules and the dermis. In confirmation of these observations urea disorganizes the