Investigation of the Structure of the Cornified Epithelium of the Human Skin* by A. Gedeon

The structure of cornified tissues, such as hair, wool, nail, and cornified epithelium of the skin, has been investigated largely by polarization optical, x-ray diffraction, or electron microscope methods. Under the polarization microscope all these tissues show a positive double refraction which is considered due to regular arrays of asymmetric keratin particles (12). X-ray diffraction studies reveal the presence of an ¢x-type of keratin, built up of parallel-oriented and somewhat contracted polypeptide chains, showing a characteristic axial periodicity of 5.1 A (1, 2, 4, 5, 9, 10). By means of the electron microscope long protofibrils were demonstrated in cortical ceils of wool, measuring about 110 A in width and 2000 A in length (7). These protofibrils were considered as the smallest submicroscopic units of keratin, building up the microscopic tonofibrillae (10). Although x-ray analysis of the hair, nail, and cornified epithelium of the skin shows that their structures are built up of similara-type of keratins, differences occur in the direction of principal orientation of molecular chains in these various cornified tissues. In the cortex of the hair, the long axis of molecular chains was found to run parallel to the longitudinal axis of the hair, coinciding with the direction of growth (1, 2, 12). In the nail, the chain molecules were observed to lie perpendicular to the longitudinal axis of the nail plate, hence perpendicular to the direction of growth (5). In the only stratified squamous epithelium heretofore regarded as suitable for x-ray study, i.e., snout of the cow and horse burr (4, 9), the chain molecules run parallel to the surface plane and perpendicular to the direction of growth. Accordingly it appears that while similar molecular chains of keratin are formed in all these epithelial elements their ultimate orientation is determined by different mechanisms in various comified tissues.