DEMONSTRATION OF SPECIAL PARASYMPATHETIC NERVEFIBRES IN THE DORSAL OR POSTERIOR ROOTS OF THE LUMBAR REGION OF THE SPINAL CORD

The commonly received hypothesis that the vaso‐;dilator effects seen on stimulation of the dorsal roots of the spinal nerves in the thoraciclumbar regions of the cord are produced by antidromic impulses passing down the sensory fibres of those roots is incorrect. Evidence is adduced of the presence of numerous fine medullated fibres in the dorsal roots which have their origin in small nerve‐cells in the grey matter at the base of the dorsal horn of the cord, the axis‐cylinders of which pass as fine medullated fibres into the dorsal roots (accompanying the entering sensory fibres), and pass into the dorsal root ganglia. They are there connected by synapse with special nerve‐cells from which other fine medullated fibres come off. These emerge from the ganglion and pass peripherally into the mixed nerve and its branches. Histological examination of the nerve‐fibres of the dorsal roots after section both beyond the ganglion and between the ganglion and the cord affords clear evidence of the above statement. This evidence is obtained from the result of section of the dorsal root between the ganglion and the cord in producing or in failing to produce Wallerian degeneration of the nerve‐fibres in question in the parts of the severed root distal or proximal to the cord respectively, and in the observation of the changes which occur in certain cells of the cord after such section. It is concluded that the centrifugal small medullated fibres in question represent the parasympathetic fibres of the autonomic system of Langley in the thoraciclumbar region of the cord, and that their presence is sufficient to account for the so‐called “antidromic” impulses, which have been supposed to travel (centrifugally) down the sensory nerve‐fibres.