DIFFERENTIATION AND PROTEIN SYNTHESIS 



( >7 



sheath, and the central core, the medulla, may be classed together, since 

 they each form a peculiar protein called trichohyalin (probably very 

 similar to the keratohyalin of the skin). It forms as amorphous droplets 

 and is later converted into a fibrous form. Chemically it is distinct from 

 keratin and is unique in containing the amino acid citrulline (6 per cent 



7 6 5 4 3 2 1 



LAYERS FROM OUTER ROOT SHEATH 



Fig. 42. Purely diagrammatic representation of the relations of the 

 several cell streams (1-7) in the hair follicle to the basal membrane M and 

 the outer root sheath to illustrate the " position " theory of differentiation. 

 The intercellular gaps are emphasized. C is a melanocyte, the papillary- 

 space is to the left. The dense dots in the inner root sheath cells (Huxley 

 and Henle layers and cuticle 2) are trichohyalin. 



by weight) (Rogers, 1959). The other concentric cylinders form the 

 cuticle and cortex of the hair, each containing a distinct variety of keratin 

 (Fig. 42). 



In respect of their developmental history, the cells of the bulb are 

 equipotential and could apparently proceed to synthesize any of the 

 epidermal products. The sole factor, which initially seems to distinguish 



