Abstract
Studies on the spinal cord of amphibian embryos have demonstrated the remarkable regenerative powers of the central nervous system in these forms. The cord may be completely severed in frog embryos and tadpoles up to the time of metamorphosis and will restore anatomical and physiological continuity in a high percentage of cases. In the earlier stages, the removal of a segment of the cord one or two myotomes in length is followed by complete reëstablishment of anatomical continuity in most cases. Where restoration of anatomical continuity fails for various reasons, the regenerated or developing nerve fibers have grown toward the opposite cut end of the cord, sometimes by unusually tortuous routes.
A series of experiments on young embryos in which a segment of the spinal cord was removed, rotated on its long axis and re-implanted, gives further indication of the existence of an attracting stimulus as a factor in reëstablishing the continuity of the cord.
These experiments indicate that it is possible to obtain reestablishment of anatomical continuity between a portion of the cord in its normal position and a segment which has been rotated on its long axis through various arcs up to complete inversion (180° rotation). The restoration of physiological continuity has not been conclusively demonstrated, though there is now much evidence that it has occurred. Better healing is obtained when the segment is rotated up to 90° than when it is rotated more. When rotated 90°, there is a tendency for the regenerated tissue closing the cord wound to rotate through the quarter turn of a spiral to link up the like fiber tracts. This same tendency is present in rotations of from 90° to 135°, but is not so clearly demonstrable.
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