158 



KERATIN AND KERAT I NI ZAT IO N 



It can be ascertained by passing a wire, bent into the form of a sine 

 curve, through a short length of flexible tubing held at the end from which 

 the wire emerges, that the movement leads to an oscillation in the cur- 

 vatures of the free end. Thus in the case of the crimped fibre, the passage 

 of the hardened hair through the upper portions of the follicle (fixed end) 

 will tend to cause an oscillation in curvature of the softer, lower portions of 

 the follicle (the analogue of the free end) (Figs. 66 and 67). A feed-back 



(a) (b) (c) 



Fig. 67. Successive stages in the production of a full crimp wave. 



(a) A segment 1 of curvature + R is passing along the neck B and 

 emerging through the fixed orifice. At the lower end of B a segment 2 

 of radius — R is about to enter B. 



(b) The segment 2 has entered B and has deflected the neck B into the 

 opposite curvature — R by the time it is about to emerge. By deflecting 

 B into this shape it has deformed the setting zone C into the reverse 

 curvature -f Rso that the length of fibre 3 being hardened at this point 

 will now have the reversed curvature. 



(c) Segment 3 has now entered the upper levels swinging them over to 

 the original shape + R and the effect on the lower levels is to reverse the 

 curvature there. 



Thus the curvature in the " setting zone " is maintained in an out-of- 

 phase condition relative to the upper zone by the mechanical feed-back 

 link. Growth conditions on the inner face of the curved zone C of Fig. 

 66 and the adjacent zone of the bulb D are assumed to be less favourable 

 than on the outer face and to result in less rapid growth on that side. 

 Assuming further that growth in the bulb is also periodic, the rate, quality 

 (o or p) and size of outer root sheath also swing from side to side. This 

 oscillation may also resonate with the mechanical vibration in zones B 

 and C, the asymmetric growth giving rise to a curved segment to enter in 

 phase with the curvature of the zone C. 



