V EPITHELIALIZATION CHEMICAL CHANGES 687 



autografts (Scothorne and Scothorne, 1953). Methylcholanlhrene-treated mouse 

 skin (Biesele, 1944) and certain skin tumors (Stowell, 1947) follow a similar 

 pattern. 



The deoxyribosenucleic acid (DNA) content of the nuclei in normal epithelium 

 presents a gradient similar to that of cytoplasmic RNA. Hardy (1952) observed 

 in mouse skin that DNA is most concentrated in the nuclei of cells occupying 

 the basal and lower stratum spinosum layers. Skin, proliferating in excess of the 

 normal rate, contains larger quantities of DNA per unit volume and per cell. 

 This has been shown by photometric measurements of the Feulgen reaction in 

 methylcholanthrene-induced mouse cancer (Stowell, 1942), in human epidermoid 

 carcinoma, and in hyperplastic lesions (Stowell and Cooper, 1945). Although not 

 measured by photometric means, the Feulgen reaction when applied to rat and 

 human wounds seems to reflect the same direct relationship between mitosis and 

 DNA concentration (Washburn, 1954a, c). 



The alkaline phosphatase content of normal skin is low. In epithelium it is restricted 

 to the stratum granulosum and appears to be associated with the keratohyalin 

 granules in mice (Hardy, 1952), guinea pig (Bourne, 1943), and human skin 

 (Fisher and Click, 1947; Pirila and Eranko, 1950). Histochemical studies of this 

 enzyme using the Comori (1939) technique are difficult to evaluate because of 

 the well known diffusion phenomenon. The subject has been thoroughly discussed 

 by Goetsch et al. (1952) and Pearse (1953). Most evidence, both histochemical 

 and biochemical, indicates that alkaline phosphatase is present only in the cyto- 

 plasm (Martin and Jacoby, 1950; Palade, 195 1). 



When epithelium is stimulated either by application of methylcholanthrene 

 (Biesele and Biesele, 1944) or during wound healing (Fell and Danielli, 1943), 

 the quantity of epithelial alkaline phosphatase increases at the time when the 

 underlying dermis is also rich in this enzyme; hence, difTusion is a possible 

 explanation. More recently, the migrating epithelium has been examined 

 following freeze-dry fixation and staining by both the Comori (1939) and Seligman 

 (Seligman and Manheimer, 1949) techniques (Washburn, 1955). There is an 

 increased phosphatase activity especially in the lower layers of the epithelium, 

 where it ordinarily does not exist. The role of this enzyme in the skin is not under- 

 stood although it may be related to keratinization, which would account for its 

 increase in migrating epithelium or in areas where cornification does not occur. 



Acid phosphatase is present in the keratinized layers of normal epithelium. It can 

 best be detected following the staining of frozen or frozen-dried specimens (Mes- 

 con, 1950; Moretti and Mescon, 1956). During healing no increase is apparent 

 at the wound edge and the migrating epithelium is completely devoid of this 

 enzyme since no keratinization takes place. 



There is an inverse relationship between succinic dehydrogenase and non-specific 

 esterases in normal skin, dependent upon the degree of cell activity. In the resting 

 phase of the hair cycle the esterase content is high while succinic dehydrogenase 

 is low (Argyris, 1956a). According to Argyris, (1956b) during the growth phase of 

 the hair cycle, in fetal skin, or in migrating epithelium following wounding, the 

 pattern is reversed and succinic dehydrogenase is increased; he assumes that 

 succinic dehydrogenase is related to the energy requirements of the cell. Areas 



Literature p. 703 



