THE KERATINIZATION PROCESS 247 



Mercer (1947) to account for the appearance of fragments of reduced and 

 ethylated wool fibres produced by enzymatic digestion. 



The analysis of " solutions " of keratin was not at first productive but 

 with the introduction of peracetic acid as the agent for breaking disulphide 

 bonds (p. 238) clear-cut results were obtained. The separation of a fibre- 

 forming a-component and a non-fibrous sulphur-rich y-component from 

 solutions of oxidized wool led Alexander and Hudson in their book (1954) 

 to propose unambiguously a crystallite-plus-matrix model for keratin. 





:&: Matrix (^-keratin) 

 # Filament {a -keratin) 



Fig. 102. The " filament plus matrix " model for a fibril of fibrous 



keratin. The filaments consist of bundles of a-helices (see p. 183) and 



are embedded in an amorphous matrix with a higher cystine content. 



See also Fig. 98, p. 225. (Birbeck and Mercer, 1957.) 



Strong, directly-morphological evidence from intact material was later 

 forthcoming when it became possible to examine electron-microscopically 

 (see p. 223) sections of developing hairs. Birbeck and Mercer (1957) 

 concluded from the pattern of osmium deposition in the hair fibrils (Plate 



15) the existence of a system of filame.its embedded in a sulphur-rich 

 matrix (Fig. 102). This was confirmed in fully-hardened hair, wool (Plate 



16) and quill by Rogers (1959). Brody (1959) (Plate 17) demonstrated a 

 similar pattern in the epidermis. 



The existence of a filamentous system prior to, and distinct from, the 

 finally stabilized keratin, is demonstrated by X-ray methods (p. 211), by 



