THE SKIN 201 



Eleidin containing Layer (Stratum Lucidum). The granule 

 cells are abruptly transformed into the shiny cells of the stratum 

 lucidum, which is the deepest layer of the horny portion of the 

 epidermis. The cells of this layer possess an indistinct nucleus, 

 are irregularly flattened and angular in shape, are more or less 

 fused together at their adjacent margins, and contain a smooth, 

 highly refractive, glassy cytoplasm which reacts feebly to most 

 staining reagents, but is deeply colored by safranin. 



The stratum lucidum is so named because of its highly refrac- 

 tive appearance ; it is usually about two cells thick. Its cytoplasm 

 contains eleidin, a substance which is probably intermediate in 

 chemical composition between the keratohyalin of the stratum 

 granulosum and the keratin of the horny cells. 



Flattened Cell Layer and Scaly Layer (Stratum Corneum and 

 Stratum Disjunctum of Ranvier). Above the stratum lucidum 

 the horny layer consists of flattened cornified cells which are 

 closely packed and somewhat fused and blended with each other 

 at their faintly serrated margins. Intercellular bridges and spaces 

 have almost entirely disappeared. The nuclei of the cells are no 

 longer demonstrable, and their cytoplasm has been changed into 

 a dry, shiny, highly refractive mass of keratin which responds but 

 slightly to ordinary stains. If, however, these cells are acted upon 

 by solutions of strong alkalies, soda, potassa, etc., the outlines of 

 the degenerated nuclei reappear. As the cells are pushed nearer 

 the free surface, by the process of cell division in the deeper layers 

 and the coincident desquamation of cells from the free surface, 

 they become more and more flattened and desiccated and more 

 completely and firmly fused together until at the surface they 

 form the partially detached cell masses or scales scaly layer, 

 stratum squamosum which are eventually removed by continued 

 desquamation. 



As Kanvier* has shown, sections of the epidermis which have 

 been fixed in osmium tetroxid solutions are peculiarly blackened 

 by this reagent. The horny layer only, reacts to the osmium, its 

 superficial scaly layer as well as the deepest portion of the flat- 

 tened cell layer being blackened by the reagent. The intervening 

 portion of the horny layer is not stained with osmium except at 

 the free margins of the tissue. Hence this reaction would seem 

 to demonstrate the presence of a fatty material (epidermal fat) 



* Traite technique d'histologie ; also Arch, d'anat. mic., 1900. 



