The Proteins of the Hah- Follicle 



159 



Fig. 1. Diagram of the hair follicle showing the development 

 of the fibrous structure of the cortex. On the right-hand side 

 is shown the rise in birefringence (A/;): in the centre the 

 ,\-ray diffraction patterns at several levels are indicated in 

 circles; on the left-hand side the changes in cell shape. 



The two birefringent systems are well defined 

 when the follicle is viewed between crossed polaroids 

 and measurements (3) show in the coitex a continuous 

 rise in birefringence at the level of the follicular 

 constriction. In the Henle layer of the sheath the 

 change from the isotropic to the birefringent state 

 occurs in a single sudden step, suggesting a rapid 

 transformation of the cell contents. A slower rise 

 occurs in the Huxley layer and the sheath cuticle. 

 The comparison of precisely the same fields in the 

 polarising microscope and the electron microscope 



has enabled tlio birefringence to be correlated with 

 structure. 



The inner root sheath. This correlation is most 

 complete in the Henle layer of the inner root sheath. 

 By examining in the electron microscope the area 

 in which birefringence first appears, we can see in 

 some detail the formation of the fibrous form. The 

 rounded, structureless, dense bodies, which appear 

 lower down in the cytoplasm of the sheath cells and 

 rapidly aggregate to form the large droplets recogni- 

 sable in the light microscope as trichohyaline, are 

 seen transforming into fibrils. The details of the 

 actual transformation are shown in fig. 2. Fine fila- 

 ments (about 100 A diameter) can be seen extending 

 in both axial directions from the lenticular shaped 

 droplets of the amorphous form. The transforma- 

 tion occurs entirely intraccllularly and ditTers from 

 anything previously described, although the forma- 

 tion of fibrils from solutions of corpuscular mole- 

 cules is well known. It would seem that the filaments 

 "crystallise" out on the surfiice of the solid droplets 

 and are pushed away from the surface by their 

 continued growth. The nearest physical analogue 

 would be the growth of single crystals from the 

 molten state. Little is known of the chemical com- 

 position of trichohyaline to assist our speculations 

 and the amounts present in the hair are too small 

 to make it possible to examine it by x-ray difTraction. 



In the other layers of the sheath (Huxley and 

 sheath cuticle) a similar transformation occurs. 

 However, it takes place more slowly and the amor- 

 phous and fibrous forms can be seen together, in 

 the same cells, for a distance of several hundred 

 microns above the constriction. 



The cortex. — A very different course of events 

 occurs in the cortex. Here the fibrous form appears di- 

 rectly in the form of fine filaments (60-80 A in width) 



Fig. 2. Electron micrograph of a portion of a Henle cell of the inner root sheath at the point of transformation of the 

 elongated trichohyaline droplets into filaments. (Longitudinal section.) Magnification 73,000. 



