168 



KERATIN AND KERATINIZATION 



example, in the case of collagen which shows a well-marked long spacing 

 of 640 A, the electron-microscopic image reveals the same fundamental 

 period. 



Yet even in this instance, in which a relatively-large amount of data 

 from many sources is available and the basic arrangements of the poly- 

 peptide chains as a triple chain helix are precisely known (see p. 127), 

 the nature of the major spacing and the many subspacings visible electron- 

 microscopically is still under discussion (Hodge, 1960). 



Fig. 69. Drawings of the respective wide-angle and pinhole small-angle 

 patterns of clam ( Venus) muscle. The fibre-axis direction in all patterns 

 is vertical. M is the prominent composite meridional arc at 5'1 A, E the 

 equatorial diffraction at 9'6 A, these being the characteristic a-pattern 

 diffractions at wide angles referred to in the text. L in the left diagram 

 marks the small-angle series of diffractions which are indicated in greater 

 detail in the right figure. Adapted from Bear (1951). 



With keratin the situation is much less satisfactory. Convincing 

 electron-microscopic observation of the longitudinal spacings is wanting. 

 Filaments can be observed both in growing hair and in disintegrated wool 

 which have diameters of the expected order of 60-100 A and the packed 

 array of these may be responsible for the lateral spacings (Birbeck and 

 Mercer, 1957a; Rogers, 1959) (Plates 15 and 16). Fibrils in disintegrated 

 wool (Farrant et al., 1947; Jeffrey, Sikorski and Woods, 1956) and in 

 extracted sections of skin (Porter, 1956) have a quasi-regular nodular 

 appearance which does not possess a periodicity of the expected order 



