Abstract
Nerve regeneration is the result of a growth process starting from the cut ends of those parts of the severed neurones left in connection with their cell bodies. Extensive bifurcation of the outgrowing sprouts is supposed to provide for overabundance of peripheral terminations. To what extent the excess of innervation is kept within bounds, and by what factors, has not yet been determined. Observations showing that the number of regenerated nerve fibers in supernumerary transplanted limbs is of the order of that of a normal limb, irrespective of the size of the nerve source, (Weiss 1 ) suggested the existence of peripheral influences controlling the amount of fiber regeneration.
Following this lead, a series of experiments was undertaken on adult specimens of the Japanese newt, Triturus pyrrhogaster (Boie). Operations were performed on the brachial plexus (spinal nerves 3, 4 and 5) of one side, the opposite side serving as control. After the operation, 120 days were allowed for nerve regeneration, whereupon experimental and control limbs were fixed and treated by Bielschowsky's silver method. Nerve counts were made in cross sections at 3 representative levels (H, proximal humerus; E, elbow; W, proximal wrist), and the percentage difference between the number of regenerated fibers in the operated limb and the number of original fibers in the control limb was calculated.
Experiment I. (7 cases.) Transection of all brachial nerves at the shoulder level. A fiber deficit was found in the regenerated nerves, the average percentage difference amounting to, at H: 15.4%; at E: 27.2%; at W: 45.6%. This deficit seems to parallel a certain atrophy of the denervated and re-innervated limbs, the average reduction of their cross-sectional area being 21.5%. The number of nerve fibers entering the limbs (at level H) is, therefore, grossly speaking, of the same order before and after nerve regeneration.
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