160 



M. S. C. BIRBECK AND E. H. MERCER 



Fig. 3. Electron micrograph showing fibrils of keratin appearing in a cortical cell in the upper bulb region (longitudinal 

 section). Magnification 20.000. Fig. 4. A cross-section at high magnification of a fibril showing the component keratin 

 filaments (light) on a dark ground — the cystine-rich matrix. Magnification 150,000. 



without any evidence of a non-fibrous precursor. 

 Filaments can be detected electron microscopically 

 in the bulb cells at a level below which the bire- 

 fringence is strong enough to be demonstrated. Such 

 filaments are oriented parallel to the fibre from their 

 first appearance. These observations clearly show 

 that the keratin is not synthesised as an amorphous 

 precursor which is converted into a fibrous form by 

 its passage through the narrow neck of the follicle. 



In the upper bulb, where the rise in birefringence 

 takes place, the cells rapidly fill with filaments (fig. 3) 

 and condense to form the rather definite structures 

 recognisable in the light microscope as fibrils (0.1- 

 0.2 /< in diameter). At this level there is sufficient 

 material present to enable an x-ray diffraction photo- 

 graph to be made and a typical a-type pattern results 

 (fig. 1). There is therefore little doubt that the long 

 fine filaments are the structures responsible for this 

 x-ray pattern which is of such interest to crystal- 

 lographers (2). 



Cross-sections of the condensed fibrils (fig. 4), 

 show that the filaments are embedded in a 

 material which, after osmium fixation, has a greater 

 electron scattering power than the filaments them- 

 selves, i.e. the filament sections appear light on 

 a dark ground. The most probable interpretation is 

 that the osmium is here acting as a specific stain for 

 cystine (cysteine) and that the S sites are concentrated 

 in the interfilamentous regions. Since chemical an- 

 alysis of dissolved hair (1) shows the presence of a 

 fibrous component (a) with a low S content and an 

 amorphous component (;') with a higher S content, 

 we suggest that the a-component be identified with 

 the fine filaments and the y with the interfilamentous 

 cement. Fibrous keratin is thus seen to be a complex 



of "filaments plus matrix" rather than a single 

 entity. 



An unsolved question is the contribution to the 

 observed birefringence of intrinsic and form factors. 

 Attempts to determine these contributions by the 

 standard method of immersing the hair in a series 

 of liquids is not possible, since these invariably fail 

 to penetrate. Liquids, which do penetrate the hair, 

 either react with it chemically or swell the entire 

 structure. In either case the double refraction falls, 

 usually irreversibly, to a low value. The structure 

 of fine filaments embedded in a highly cross-linked 

 matrix suggested by electron microscopy may explain 

 these results. The hair is certainly a Wiener body, 

 i.e. a system of oriented rodlets embedded in a 

 matrix, probably with ditTerent optical constants, 

 and there is likely to be a form contribution. But, 

 since the matrix is by far the more cross-linked 

 component, suitable imbibition liquids penetrating 

 the matrix alone probably do not exist. 



This investigation has been supported by grants to the 

 Chester Beatty Research Institute (Institute of Cancer 

 Research: Royal Cancer Hospital) from the British 

 Empire Cancer Campaign, Jane Coffin Childs Memorial 

 Fund for Medical Research, the Anna Fuller Fund, and 

 the National Cancer Institute of the National Institutes 

 of Health, U.S. Public Health Service. 



The authors are particularly grateful to Mr. K. G. 

 Moreman for supplying the illustrations. 



References 



1. Alexander, P. and Hudson, R. F., Wool, Its Chemistry 



and Physics. Chapman and Hall, London, 1954. 



2. AsTBURY, W. T., Proc. Roy. Soc. B 134, 303 (1947). 



Review. 



3. Mercer, E. H., Biochim. et Biophys. Ada 3, 161 (1949). 



