32 EFFECTS OF IONIZING RADIATION Pyknosis of cells of the basal layer was commonly seen. Focal disorganization of the malpighian and basal layers was usually present in the more extensively damaged arcades (Plate 23). Cells laden with pigment ‘were frequently present throughout the epidermis and intercellular pigment was noted in some sections. The stratum granulosum was usually atrophic or even absent. Imperfect keratinization with parakeratosis was visible in all sections. The stratum corneum was loosely fibrillated and hyperkeratotic. The arcades of minimal damage were usually found in areas where sweat ducts approached the epidermis (Plate 22). There was an apparent increase in the numberof cells and mi- totic figures along the neck of the ducts and the adjoining areas where regeneration was underway. Inthese areas the stratum granulosum appeared almost normal in width. In contrast to the more severely damaged areas where pigment was increased, these areas of minimal damage showed an actual decrease, being almost free of pigment. Dermis. Changes in the dermis were confined largely to the pars papillaris and superficial pars reticularis (Plates 21-24). Mild edema in some cases were noted. Capillary loops were often indistinct and when discernible they frequently were associated with an increased number of pericytes. The endothelial cells showed swelling and were polygonal in shape. ‘Telangiectatic changes were noted in these areas where the overlying epidermis showed greatest damage which were associated with perivascular lymphocytic infiltration. Chromatophores, filled with melanin were prominent in the superficial dermis. Thefineelastic fibrils runninginto the pars papillaris were often altered or absent. Little if any damage was seen below the superficial pars reticularis. The hair follicles were narrow and in most instances devoid of shafts in this region. There was sometelangiectasis of the capillaries and slight mononuclear cell infiltration. Some of the large elastic fibers in this region showed slight swelling in some cases. No damageto fibrocytes orcollagen fibers was noted. Second series—7th and 8th weeks post-exposure. Eydermis. In general, reparative processes of the epidermis had proceeded, except for a few persistent areas of atrophy with narrowing of the epidermis and finger-like downgrowths of the stratum malpighii (Plate 27). These changes occurredin areas of the greatest narrowing of the stratum granulosum. In such areas the basal cells often showed increased pigment. There were many outward epidermal excrescences covered by thickened stratum corneum,still loosely laminated (Plate 25), which probably accounted for the “orange-peel” appearance of the skin noted grossly. In almost all instances the basal layer was intact withlittle or no disorganization. There were a few scattered areas in which occasional epithelial cells with pyknotic nuclei and perinuclear cytoplasmic halos occurred in the malpighianlayers (Plate 26). There were occasional arcades in which the epidermis and particularly the stratum granulosum appeared to be widened. These occurred primarily in relation to contiguous sweat gland ducts where the latter penetrated the epidermis. A narrow zone of parakeratosis and amorphousdebris wasstill present between the stratum granulosum andtheloosely laminated stratum corneum. The stratum lucidum was not apparent. Dermis. The capillary loops in the dermal papillae were not uniformly distinct. Pericytes remained in increased number but fewer lymphocytes were present. Generally, there was a slight telangiectasis of the capillaries in the pars papillaris and the superficial pars reticularis (Plate 27). There was some edema of the pars papillaris (Plate 25). Scattered pigment-laden chromatophores were irregularly distributed in the papillary layer (Plate 26). In somecases hair shafts in the superficial pars reticularis were narrowor absent; in others the hair shafts appeared normal. Small hair follicles (Plate 25) and sweat ducts in somecases showed mild atrophy.