686 



WOUND HEALING 



Other possibilities exist? The principal physiologic activities of epidermis are 

 mitosis and keratinization. The only circumstance in which glycogen accumulates 

 is when keratin production is absent, e.g. in fetal skin, in cells of the migrating 

 margin of either wounds or tissue cultures and in areas where epithelium occurs 

 without keratinization (soft palate). When keratinization starts, the glycogen 

 disappears; this suggests an increased rate of glycolysis which may be related to 

 greater energy requirements. 



Cells undergoing active protein synthesis have been repeatedly shown to con- 

 tain relatively large quantities of cytoplasmic ribonucleic acid (RNA) . In normal 

 epithelium, the activity of the lowermost cells is concerned with mitosis while 



Fig. 10. Photomicrograph of same specimen as Fig. 9 showing absence of glycogen following 

 digestion with diastase (Periodic Acid-Schiff stain, x 105). 



that of the upper layers is related to keratinization. Brachet (1942) was the 

 first to observe by histochemical methods that an RNA gradient existed in 

 epithelium. He noted in amphibia that the cytoplasm of cells occupying 

 the basal layer was relatively rich in RNA in contrast to cells located in the 

 stratum corneum. This finding was confirmed by Hardy (1952) in mouse skin 

 and by Nolte (1947) in the human toe. Biochemical assays in terms of nucleic acid 

 phosphorus have also substantiated the presence of RNA in skin (Davidson and 

 Waymouth, 1944a). 



During wound healing the epithelium initially migrates without the aid of 

 increased mitotic activity and the RNA pattern resembles that of normal skin. 

 When the mitotic rate increases, the cytoplasm of the cells contains a larger 

 amount of RNA, as observed in mouse (Clement, 1944), guinea pig (Firket, 

 195O5 ^^d ^^t wounds (Washburn, 1954c), during wound healing, and with 



