Fig. 6. Electron micrograph of myelin sheath segment from transverse sec- 

 tion of frog sciatic nerve, showing uniform preservation of fine structure and 

 regular arrangement of concentric layers consistently obtained with low- 

 temperature preparation techniques. Osmium-cryofixation preparation, low-tem- 

 perature embedding (-20' C) in mixture of methyl acrylate and butyl-methyl 

 methacrylate. X 1 20,000. 



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