136 



MACROMOLECULAR COMPLEXES 



Fig. n. High-resolution electron micrograph of myelin sheath segment 

 from transverse thin section of frog sciatic nerve, showing granular structure 

 of concentric layers (arrov^s), with a modified regular period of 50 to 60 A 

 which probably results from enhancement of the intermediate line by treatment 

 with bromine. Bromine-cryofixation preparation. X450,000. 



expanded. The protective effect of glycerol on the myelin structure 

 could be clearly established by showing that the diffraction pattern 

 was not changed after rapidly freezing the glycerol-treated nerve 

 with liquid nitrogen (-195° C) or liquid helium I (—269° C), then 

 thawing. By contrast, the pattern of untreated nerve, which was 

 subjected to the same type of freezing and thawing, exhibited 

 pronounced modifications, indicating a partial breakdown of struc- 

 ture. In the course of this work it was also found that glycerinated 

 nerves could be preserved in an essentially unaltered state for 

 periods of several weeks at room temperature, whereas fresh nerve 

 kept in normal physiological saline degenerated within a few days. 

 Only when nerve is kept at 4° C is the disintegration process re- 

 tarded, but even then the state of preservation cannot compare with 

 that of glycerinated nerve. This objective evidence of the extensive 

 protective action of glycerol on myelin ultrastructure emphasized 



