78 KERATIN AND KERATINIZATION 



of Montagna. The " scale-hair-gland " unit is more general and 

 plausibly explains some aspects of the mammalian hair pattern, if we 

 suppose that the ontologically-earlier preparations are directed towards 

 the formation of the entire unit and that later the separate single com- 

 ponents come to develop to different degrees leading at last to the non- 



FlG. 35. The basic trio group (11 '1') of primary hairs associated with 

 bilobed sebaceous glands (cf. Fig. 34) and the secondary hairs (22) which 

 appear later arising either de novo or from out-pocketing of the outer 

 root sheaths of the original primaries (Hardy and Lyne, 1956). The 

 entire cluster is marked off from its neighbours by bundles of collagen 

 fibres in the dermis. Redrawn from Carter (1943). 



appearance of the scale. Hairs retain a clear sensory function as an 

 accessory mechanical lever for the stimulation of the nerve endings 

 associated with them. 



Other possibly keratinized structures 



A small amount ( ~ 2 per cent by weight) of a resistant, sulphur- 

 containing protein, usually referred to as a keratin, is found in the enamel 

 of teeth where it may contribute towards the bonding of this highly 

 crystalline, inorganic material (Scott, 1955). The enamel layer of a tooth 

 is a secretion of modified epidermal cells and thus any keratin it contains 

 would be a secreted protein. The formation of a tooth has already been 

 discussed on p. 74 and its components (partly dermal, partly epidermal) 

 may be seen in Fig. 32 which shows a section of a developing tooth. 



The cystine content and basic amino acids of the organic matrix of 

 enamel have been determined (Battistone and Burnett, 1956; Hess, 1953; 

 and Block et al., 1949). The cystine is low for a keratin (0-2 per cent) and 

 the ratios of the basic amino acids show it to be a pseudokeratin as defined 

 by Block (see p. 31). Hydroxyproline, usually associated with collagen, is 

 reported by Hess et al. (1953) and by Battistone and Burnett (1956). The 

 X-ray pattern is suggestive of keratin rather than of collagen (Pautard, 

 1961). 



