THE GROWTH OF EPIDERMAL STRUCTURES 



157 



of cybernetics, that such a regularity of form in changing conditions could 

 only be maintained by information transfer. It remains, however, to 

 identify the links in the feed-back train. 



The histology of the wool follicle has been much studied and a very com- 

 plete account given by Auber (1950). Problems relating to crimp for- 

 mation are discussed by Wildman (1932), by Rudall (1936) and also by 



Fig. 66. Theory of crimp formation in a wool follicle (see text). The 

 following structural elements are distinguished: 



(a) The point of emergence of the fibre from the skin. The fixed 

 orifice. 



(b) The upper reaches of the follicle which contain a set and perman- 

 ently curved segment of fibre with radius of curvature R. 



(c) The keratinization zone. The "mould" of curvature — R (opposite 

 to that in segment B) in which the growing fibre is " set " with a cur- 

 vature — R. 



(d) The bulb, the origin of the rodlet of protein which enters the zone C. 

 For the purposes of clearer illustration, the geometry of the follicle has 

 been simplified and idealized. The situation depicted shows the follicle 

 in an extreme position in which C is shown in its extreme extent to the 

 right. O and P indicate the locations of the two types of keratin ortho- 

 and para- (see p. 273). 



Auber (1950). We shall return in Chapter 6 to special questions relating 

 to keratinization in curved follicles. For our present purposes the structural 

 elements likely to be involved in crimp production and maintenance are: 

 the deflected bulb, the curved follicle and the (usually) asymmetric placing 

 of the hair structures within the outer root sheath (Fig. 114). 



