Abstract
When the developed limb of a urodele amphibian is amputated, masses of mesenchym accumulate at the wound and by subsequent growth and differentiation produce a new limb. Concomitantly, nerve fibers sprouting from the severed old nerve trunks invade the regenerating limb and provide its nerve supply. This process, studied in a preliminary manner by Weiss and Walker, 1 was given a more thorough examination in the present study.
Adult specimens of the Japanese newt, Triturus pyrrhogaster (Boie) and Mexican Axolotls were used, the latter in 2 different size (age) groups (75-85 mm. and 120-150 mm. in length). Fore limbs were amputated at the body wall and allowed to regenerate. After varying periods of time, the regenerated limbs were preserved and sectioned. In the newt, Bielschowsky's silver stain for axons proved successful, while the data concerning the Axolotl are based mainly on myelin stains (Weigert-Pal). Tests in which 2 opposite limbs of the same animals were treated by the 2 different methods, staining on one side all fibers, on the other side the medullated fibers only, revealed that in regenerated fore limbs, 75-80% of the fibers are medullated. Every 20th cross section (cut at 10 micra) was measured, and the amount of nerve fibers contained therein was counted.
The number of nerve fibers present in the old limb base proximal to the level of amputation was rather constant: cca. 900 and 1200 fibers in the smaller and larger Axolotls, respectively. Distally to this level, in the regenerate, the number declines gradually in such regular manner that a definite relation between nerve supply and mass of innervated tissue suggested itself. The relation was revealed by the graphs in which the data were plotted, to be a remarkably simple one: If a regenerate is divided up into a series of slices of 200 micra each; if vs is the mass of one of these slices; and if the number of nerve fibers terminating in this slice (determined as the difference between the nerve numbers counted in the 2 levels bounding the slice) is ns; the ratio
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