THE SPINAL CORD AS A CONDUCTING PATH 



621 



other facts which, however, do not put the general applicabihty of 

 this law in question. I also omit for the present the structural and 

 functional relationship existing between the spinal cord and the 

 sympathejbic system. We shall see later on that the anterior roots also 

 contain efferent fibers for the autonomic organs and that these in turn 

 send impulses to central parts by way of the rami communicantes 

 and the posterior roots. 



The Trophic Function of the Spinal Cord. The Wallerian Law 

 of Degeneration. — It has been discovered by Nasse^ that a nerve- 

 fiber, when disconnected from its cell-body, undergoes certain very 

 characteristic alterations in its structure. In applying this fact to 



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k 



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v./l» 



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Fig. 308. Fig. 309. 



Fig. 308. — Schema to Show the Course of the Degeneration Following the 

 Division of the Roots of the Spinal Cord. 



A, Division of the anterior root; B, division of the posterior root distally to spinal 

 ganglion; C, division of the posterior root centrally to spinal ganglion. The degen- 

 erated portions are indicated in solid black. 



Fig. 309. — Schema Illustrating the Course of Degeneration in Motor and 

 Sensory Neurons. 



A, Motor neuron of the anterior root; B and C, sensory neurons of the posterior 

 root. The portion separated from the cell degenerates, as is indicated by the dotted 

 lines. 



the spinal nerves, A. Waller^ succeeded in demonstrating that a cut 

 made distally to the intervertebral ganglion, leads to a degeneration 

 of both roots in an outward direction, involving finally the entire 

 nerve as far as its end-organs (secondary degeneration). Quite 

 similarly, it was shown that the division of the spinal roots centrally 

 to this ganglion gives rise to degenerative changes which pursue 

 a tjourse in opposite directions from the seat of the lesion, i.e., the 

 anterior root degenerates toward the periphery and the posterior 



1 Mailer's Archiv, 1839, 405. 



2 Compt. rend., Acad, des sciences, xxxiv, 1852. 



