tensively involved areas showed considerable atrophy with flattening of the rete pegs and in places the epidermis was reduced to a thickness of two to three cells (plates 21,23, and 24). The cells of the malpighian layer showed pleomorphic nuclei, pyknosis and cytoplasmic halos, giant cells and in a few instances mlItinucleated cells. was commonly seen. Pyknosis of cells of the basal layer Focal disorganization of the malpighian and basal layers was usually present in the more extensively damged arcades (plate 23). Cells laden with pigment were frequently present throughout the epidermis and intercellular pigment was noted in some sections. stratum gramlosum was usually atrophic or even absent. The Imperfect keratinization with para— keratosis was visible in all sections. The stratum corneum was loosely fibrillated and hyper-— keratotic. Sporadic cases showed early dyskeratosis. 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 number of cells and mitotic figures along the neck of the ducts and the adjoining areas where regeneration was underway. In these 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 entirely pigment free. Dermis, — Changes in the dermis were confined largely to the pars papillaris and superficial pars reticularis (plates 21-24). Mild edema in some cases was 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 pigment, were prominent in the superficial dermis. The fine elastic fibrils running into 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 some telangiectasis of the capillaries and slight mononuclear cell infiltration. Some of the large elastic fibers in this region showed slight swelling in some cases. No damage to fibrocytes or collagen fibers was noted. Second series - 7th and 8th weeks post-exposure. Epidermis. ~ In general, reparative processes of the epidermis appeared to have been good, except for a few persistent areas of atrophy with narrowing of the epidermis and finger-like downgrowths of the stratum malpighil (plate 27). These changes occurred in areas of greatest narrowing of the stratum granulosum. In such areas basal cells often showed accentuated pigment content. There were many outward epidermal excressences 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 with little or no disorganization. There were a few scattered areas in which occasional epithelial cells with pyknotic nuclei and perinuclear cytoplasmic halos occurred in the malpighian layers (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 amorphous debris was still present between the stratum granulosum and the loosely laminated stratum corneum. The stratum lucidum was not apparent. , Dermis. — The capillary loops in the dermal papillae were not uniformly distinct. cytes remained in increased number but fewer lymphocytes were present. Peri- Generally, there was a slight telangiectasis of the capillaries in the pars papillaris and the superficial pars reticularis (plate 27). There was sane edema of the pars papillaris (plate 25). Scattered pigment-laden chranatophores were irregularly distributed in the papillary layer (plate 26). cd Cc an 430