140 



MACROMOLECULAR COMPLEXES 



drastic alteration of the hydrated matrix, which is responsible for 

 the ordered lateral aggregation of the radially oriented lipoprotein 

 components. 



Axon Structures. While surveying the sheath-axon relation- 

 ships, it was found that a large number of the normally dense axon 

 filaments, about 100 A in diameter, showed a characteristic "hollow" 

 annular appearance (Fig. 12, a and b) with a central light area 









•^:r:i.i^-z-':. 



:t:^'-mr7^x^. ^JW, 



i: 



/ 



■w 



(n) 1000& Q 



?)iv- • 



^4' " 



Fig. 12. Electron micrographs of myelin sheath-axon segment from trans- 

 verse section of frog sciatic nerve, showing (a) fine structure of concentric 

 layers and (b) characteristic annular appearance of cross-sectioned axon fila- 

 ments which is regularly encountered in low-temperature preparations. Osmium- 

 cryofixation preparation, (a) X 250,000. (b) X 450,000. 



approximately 30 A in diameter. The edges of these ring-shaped 

 elements exhibit indications of granular fine-structure which could 

 not be clearly resolved. Although this hollow appearance of the 

 axon filaments might be due to ice-crystal artifacts, the regularity 

 of the cross-sectioned structures and the satisfactory preservation of 

 the adjacent myelin sheath would favor the assumption that we are 

 dealing with a reproducible structural pattern, corresponding to an 



