Abstract
By severing sciatic nerves in abult rabbits the author observed the degeneration and regeneration of the proximal and distal side of the severed nerves under the electron microscope and also observed variously-stained specimens of these nerves under microspectroscope, and obtained the following results.
1. The degeneration of myelinic axon on the distal side of the severed nerve occurs soon after the severance, and also the degeneration of individual nerve fibers commences ununiformly and its progress is rapid: namely, three days afterwards the majority of myelinic axons show a marked degeneration picture, and by the fifth day after the severance all the myelinic axons show a marked degeneration.
The destruction of the laminar structure of the myelin sheath can be recognized 5 to 7 days afterwards, and it gradually proceeds with lapse of the time.
2. The processes of the destruction and disappearance of the degenerated axoplasm and myelin sheath can be observed mainly in the Schwann cells.
3. On the proximal end one week after the severance regenerated axons already infolded by the Schwann cells can be observed. And by the second to third week the regeneration appears in a laminated myelin sheath formation of the regenerated axon at the proximal end and distal sutured end of the severed nerve. As for the regeneration mechanism of the myelin sheath, the findings are similar to those reported by Gerren: namely, the myelin sheath is formed by the cell membranes of the Schwann cells encircling the regenerated axon in many folds.
4. The nerve tissue of the distal side 12 weeks after the suture is still young and shows many myelinic slender nerve fibers, as compared with the normal nerve tissue.
5. When the proximal side of the severed nerve is severed again, the retrogressive degeneration observable in the proximal end of the part severed again is almost identical with that of the part severed at first: and a portion of nerve fibers show the degeneration as much as 0.3 to 0.6 cm towards the proximal side.
6. In this instance the regeneration of nerve fibers observable at the proximal end of the part severed for the second time is a little less than that of the proximal end of the part severed at first: and there can be seen a strong tendency of connective tissue proliferating in the neurom caused by severance.
7. In comparing the regenerative capacity of the severed proximal end according to the length of period between the first and the second severance, namely, those severed at the intervals of from one to 8 weeks, the regeneration of the experiment in which the second severance was made at the interval of 8 weeks is especially poor.
