124 



KERATIN AND KERATINIZATION 



produced by causes which we might group together generally as directive 

 activities operative at that level and the structures themselves are a record 

 of these activities from which we may hope to infer something of their 

 nature. 



Texture 



Possible function 



Example 



Tangles (three- 

 dimensional) 



plugging 

 holes 



blood clots 

 (fibrin) 



Sheets with 

 rodlets in one 

 plane and disordered 

 in other senses 



^ protection 



/■ — •/ against 

 v) \ impact, etc. 



epidermis 



Parallel arrangement 

 in one plane 



as membranes 



occurs only 

 transiently 



Sheets of (quasi) 

 orthogonally- 

 arranged rodlets 

 (multilayered) 



Sheets of 



hexagonally-arranged 



rodlets 



Parallel rodlets 

 in three dimensions 

 (various arrangements 

 in cross-section) 



protective 

 membranes, 

 retaining 

 basket (allows 

 movement by 

 distorting mesh) 



membrane 

 rigid against 

 distortion 



transmission of 

 •»,.. mechanical 

 ■'■'" tension 



Fig. 53. Types of fibrous texture. 



earthworm 

 cuticle (Reed and 

 Rudall, 1948), 

 amphibian dermis 

 (Plate 14B) 



peritrophic 

 membrane of 

 insects (Mercer 

 and Day, 1952) 



hairs, tendons, 

 muscles, etc. 



An apt analogy is often made between fibres, yarns and fabrics on the 

 one hand, and molecules, fibrils and tissues on the other. In this vein we 

 may speak of the spinning and weaving of molecular yarns and fabrics 

 from the raw material provided by the primary synthesis at the molecular 

 level. This primary synthesis we have already discussed, our problem here 

 is the spinning and weaving of the yarns and fabrics which we shall term 

 fibrogenesis and fibrillar organization (Fig. 54). More precisely we wish to 

 consider firstly the formation of the long fibrils (or ribbons) which are 

 used as the constructional units of the tissue and, secondly, the forces 

 which organize (or weave) these fibrils into more complex formations and 

 stabilize them. 



