266 



KERATIN AND KERATINIZATION 



110). The X-ray pattern (Rudall, 1941) shows no orientation and no 

 crystallite formation. 



(b) It has a higher sulphur content than whole hair (Geiger, 1944). It 

 forms somewhat later than the mass of fibrils in the cortex, in fact accumu- 

 lating most rapidly during the later keratinization of the cortex. We have 

 given reasons above to suppose that at this level the cortical cells have 



iLi'iniiiiiiii::::: 



(a) 



'^ 



QTrrnrrfi 



0^ 



i i ■ 

 (b) 



(0 



iMrrmmfi 



1+3+4+5 



(d) 



Fig. 110. The lamellar structure of the hair cuticle cell and the results of 

 selective removal of components. 



(a) 1 . is the resistant external cell membrane or epicuticle ; 



2. the layer of amorphous keratin or exocuticle; 



3. the inner layer of altered cellular residue; 



4. the nuclear residue; 



5. the inner cell membrane less altered than 1. 



(b) The epicuticular membrane as released by bursting AllwSrden sacs. 



(c) The keratinized residue remaining after tryptic digestion. 



(d) The " non-keratinous " residue remaining after removal of the 

 keratin (2) by oxidization and extraction. 



swung over to the synthesis of a cystine-rich, amorphous protein, y-keratin. 

 It is possible that the cuticle cells are producing a very similar protein 

 which here, in the absence of fibrils, simply condenses as an amorphous 

 heavily cross-linked mass. 



From the viewpoint of cellular differentiation, it is interesting to find 



