Abstract
The axoplasmic changes d u ring the early stages of W a 11 e r i a n degeneration of the sciatic nerves of the frog and mouse were studied by electron microscopy. The axons were examined from 12 hours to 7 days after the severance of nerve at intervals of 12 hours. The electron microscopic analysis was performed on ultrathin sections of tissues removed from the nerve at a distance about 5 mm. from the peripheral stump and fixed in buffered 1 per cent solution of osmium tetraoxide (pH 7.25 to 7.4). The results obtained are summarized as follows:
1. T he first sign of degenerative changes in the formed elements of the severed nerve fibers appears in the axoplasm in either case of the frog and mouse, but the degeneration advances more ra pidly in the nerve fibers of the mouse than in those of the frog.
2. The earliest changes in the axoplasmic entities appear in the endoplasmic reticulum which swells up and then disintegrates into fragments of minute uneven granular materials.
3. The alterations of the mitochond r ia appear somewhat later than those of the endoplasmic reticulum. The mitochondria swell up vacuollary and become filled with less electron-dense materials. The cristae mitocnondaiales diminish in number and then disappear. Subsequeutly the mitochondria are broken up into fragments and disintegrate into rough masses.
4. The degenerative changes of the neurofilaments appear either at the same time as, or slightly later than, those of the mitochondria. The first sign of alteration is loss of the preferred longitudinal orientaion of the filaments. The neurofilaments diminish in number and assume a reticulated pattern. Then they undergo complete disintegration. The diminution and reticulated changes of the neurofilaments take place between 4 and 5 days after operation in the frog nerve, and between 24 and 48 hours in the mouse nerve. The complete destruction of the neurofilaments occurs on the 6th postoperative day in the frog nerve, and on the 3rd postoperative day in mouse nerve.
5. Th e axons of the large-sized myelinated fibers degenerate more rapidly than those of the small-sized ones. The non-myelinated axon is the most resistant of all among the nerve axons.
6. As to the onset and progress of the failure of conduction of nerve impulse in degenerating nerve fiber, marked degenerative changes in the axoplasmic entities may be said to take place at a time when the excitability of nerve fibers is within normal limits. This seems to indicate that the hypothesis regarding the neurofilaments as a conduction materials is hardly tenable.
