362 



FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES 



III 



protein which are to some extent independent of each other. This 

 conflicts with the idea of these insoluble protein lamellae as frame 

 substance. 



Fig. 179 represents the submicroscopic structure of the nerve sheath 

 according to Schmidt (1937b). Neurokeratin lamellae running 

 tangentially alternate with bimolecular lipid layers. It is difficult to 

 say what the physiological significance of this foliate fine-structure 

 may be. It should be noted that if this is destroyed, say by melting 

 of the myelin substances, nerves lose their electric conductivity. 



a) 



^3 





b) 



Fig. 179. Fine-structure of medullated nerves, a) Optics. N neurofibrillar string, positively 

 uniaxial as referred to the axial direction. M myelin sheath positively uniaxial as referred 

 to radial direction (after Ambronn and Frey, 1926). h) Submicroscopic structure of the 

 medullary sheath (after Schmidt, 1937b). A lamellae of protein. L bimolecular lipid layers. 



(Further details in F. O. Schmitt, 1936; O. Schmidt, 1942; v. 

 MuRALT, 1946.) Another interesting fact is reported by Taylor (1942), 

 who found that in nerves having approximately equal conduction 

 velocities, the product of fibre diameter and sheath birefringence is 

 roughly constant. 



The laminated fine-structure of the myelin sheath, found by in- 

 direct methods, has been made visible in the electron microscope 

 (Fernandez-Moran, 1950a, b). The periodicity of the lamination is 

 80 A, which is half the long-range X-ray diffraction period of 1 5 8 A 

 reported above. 



Schmidt (1937a) detected a similar arrangement of lipid molecules 

 orientated perpendicular to the parallel layers of protein in the outer 

 members of the retinal cells in the eyes of Vertebrates, which has been 



