CHAPTER III 



Differentiation and Protein Synthesis 



In this chapter we shall discuss some general properties of epidermal 

 cells, such as differentiation and protein synthesis, which they share in 

 common with many other cells of the organism. Their more specialized 

 aspects relating to keratinization will be considered in a later chapter. 



The cytology of keratinizing cells 



A brief account of the histology of the epidermis and its derivatives has 

 already been given. For further details reference may be made to the 

 many standard texts (Maximov and Bloom, 1948; Horstmann, 1957; 

 Biedermann, 1926 and 1930; and Cowdry, 1932). The description which 

 follows is designed to draw attention to those features at the fine histo- 

 logical and macromolecular level which are particularly relevant to the 

 main themes to be discussed in later sections, or which, as a result of 

 recent electron microscopy, seem to require a redescription in terms some- 

 what different from those found in the classical works. The cytology of 

 the generalized basal layer cells and the fine structure of the dermo- 

 epidermal junction will be dealt with first. Then an account of the more 

 specialized structures of the hair and feather follicles will be given and 

 compared with that of the epidermis. 



The Basal Layer Cells* 



The intracellular equipment of the germinal cells in the basal layer is 

 similar wherever these are found, and consists of those elements which 

 are recognized as common necessities for the functioning of all types of 

 cell (p. 34) except those of bacteria and related small forms. The nucleus 

 is large and one or more nucleoli containing dense particles of the order of 

 120-200 A in diameter, may be found (Fig. 36 and Plates 4B and C, 

 7, 9, 10, 11 and 12). The nuclear contents which, except when the cell is 

 dividing, are diffuse and granular at all magnifications (as seen in electron 

 micrographs of thin sections), are strongly basic and stain positively with 

 the Feulgen technique for demonstrating desoxyribonucleic acid (DNA) 

 (Pearse, 1953). The nucleolus is Feulgen-negative, but gives positive tests 

 for ribonucleic acid (Montagna, 1956). The nuclear membrane consists of 



* Also called Malpighian cells. 



