Changes in myelinated nerve fibres caused by insulating layers.

Single myelinated nerve fibres of the frog were investigated electron microscopically and electrophysiologically. The following results were obtained. Dissected internodes exhibited small deteriorations only compared to undissected fibres. In the vaseline seal the cross section area of the axoplasm was reduced by a factor of about 3. In the air gap the corresponding figure was about 5. With electrical measurements of up to 2 h the vaseline seal did not affect the axoplasmic resistance of the belonging internode. In corresponding experiments with an air gap, the axoplasmic resistance of the internode doubled after 49 +/- 14 min (mean +/- S.D.; n = 8). Thereafter, the resistance increased rapidly up to about 3,000 times normal, depending on the atmospheric humidity. The consequences of these findings for potential clamp experiments are discussed.