THE KERATINIZATION PROCESS 



225 



towards the peripheral surface of each cell where it collects in curiously 

 patterned groups (Birbeck and Mercer, 1957). The aggregation continues 

 and with the closure of the gaps a compact layer packs against the cell wall. 

 The cellular apparatus comes to occupy the inner part of each cell and the 

 stratification thus produced persists in the final cell state. Cross-sections 

 of cuticle cells (Plate 20A) show these two layers of distinct texture, but 

 reveal also that within the keratin itself there is also some stratification 

 (Sikorski and Simpson, 1959). When reduced and stained by osmium 

 tetroxide or metal salts, the layer adjacent to the external-facing membrane 



Fig. 98. Schematic drawing of two cells in the stratum corneum of the 

 guinea-pig showing the characteristic keratin pattern with bundles of 

 filaments (F) embedded in an interfilamentous substance (IF). The cell 

 boundary consists of a fairly opaque, broad inner zone (Z) and an opaque, 

 fine outer membrane (PM). The intercellular space is filled with a 

 substance of a fairly low opacity (I). In this substance opaque, homogen- 

 eous, diffusely outlined bodies (IB) are observed. From Brody (1959). 



is more dense (probably a higher cystine content). Further, the cell 

 membrane facing the cuticle of the inner root sheath is the more dense and 

 conspicuous. This stratified structure explains many of the properties and 

 reactions of cuticles (see p. 265). 



The keratin of the cuticle is not fibrous in texture; only traces of fibrils 

 form and there is no transformation into a fibrous form as occurs to the 

 rather similar droplets of trichohyalin in the inner root sheath cells (p. 

 226). Consolidation seems to be a simple coalescence of the (perhaps 

 sticky) droplets to form the very coherent, continuous layer immediately 



