274 KERATIN AND KERATINIZATION 



Mercer, 1953 and 1954; Fraser et ai, 1954) (Fig. 114). A bilateral fibre 

 has thus a built-in tendency to maintain its curled shape and the functional 

 value of this in maintaining the insulating properties of the fleece of the 

 animal, which depend on the air trapped by the mass of crimpy fibres, is 

 obvious. 



OUTER ROOT-SHEATH 



HENLES LAYER, 



KERATINIZED 

 HUXLEYS LAYER. 

 I CONTAINING TRICHOHYALIN 

 j 'CUTICLE. PRE-KERATINIZED 



FIBRE CUTICLE 



INNER 

 >ROOT- 

 SHEATH 



CORTEX 



HUXLEY'S LAYER 

 PREKERATINIZED 



ROOT-SHEATH CUTICLE 

 PREKERATINIZED. 



----- OUTER ROOT- SHEATH 



dS0£&m&fc V _ HENL E'S LAYER. } 



Pg^'AlVBMl.4U I HUXLEY'S LAYER. (ROOT SHEATH 



L ! S^Hf J HMHi "~ " I " KERA TIN I ZED. 



mttr as.- — ;- CUTICLE, KERATINIZED.) 



"fibre cuticle 



CORTEX 



Fig. 114. The development of keratinization in an asymmetrical wool 

 follicle leading to the formation of ortho and para segments (FG and HI) 

 (see Fig. 112). From Auber (1950) by permission. The sections pass 

 through the early (D) and late (E) levels of the keratinizing zone. Notice 

 the asymmetrical root sheaths. 



Bilateral fibres of this type are widely distributed in the woolly coat 

 (secondary hair) of many animals, and are particularly marked in the sheep. 

 They are less well-defined in coarse hair and in the case of some forms of 

 crimpy negro hair are difficult to demonstrate (Spearman and Barnicot, 

 1960). The relation between external form and internal structure revealed 

 in this phenomena poses some interesting problems in keratinization which 



