STRATIFIED EPITHELIUM 



45 



ance the squamous epithelium previously described. The deeper cells have 

 a finely granular cytoplasm and distinct nuclei except when obscured by 

 the appearance of keratin within their protoplasm. Many of these cells 

 contain coarse granules of eleidin and keratohyalin substances chemi- 

 cally intermediate between the unaltered and keratized protoplasm. 



As stated, the formation of keratin within these cells is more-active 

 in those membranes which are comparatively dry from exposure to the 

 air. Consequently, it is most active in the epidermis of the skin. If 

 stratified epithelium is at all times well moistened, as, for example, in the 



FIG. 50. EPIDERMIS OF THE SKIN OF THE FINGER TIP, SHOWING EXTREME KERATIZA- 



TION OF THE EPITHELIUM. 



o, keratized epithelium; 6, Malpighian or germinal layer; c, connective tissue. 

 Hematein and eosin. X 50. 



mouth and esophagus, the formation of keratin is slight, and the soft 

 polyhedral cells compose the major portion of the epithelial membrane 

 which then has only a thin superficial covering of flattened scaly cells. 

 In the comparatively dry epidermis, on the other hand, the flattened 

 horny cells frequently occupy more than half the thickness of the epithe- 

 lial layer (Fig. 50). In the superficial squamous cells of moist membranes 

 the nucleus can ahvays be readily demonstrated, even in the keratized 

 cells of the extreme surface. Cells of the intermediate layers, especially 

 those just above the prickle cell layer, frequently show nuclei in process of 

 amitotic division. This condition is presumably associated with an early 

 stage of degeneration dependent upon a scarcity of nutriment due to 

 the relatively greater distance of these cells from the source of supply. 



