80 NERVOUS SYSTEM. 



able influence upon the nutrition of the nerves after their 

 division. Operating upon the second cervical nerves, in 

 which the ganglia can be reached without exposing the spi- 

 nal cord, Waller has demonstrated the following interesting 

 facts : * 



When the roots are divided between the ganglion and the 

 cord, the central end of the anterior root, attached to the 

 cord, preserves its normal structure, while the peripheral end 

 in a few days becomes degenerated, the tubes filled with 

 granular matter, etc., and, in short, undergoes those changes 

 observed in all nerves separated from their centres. On the 

 other hand, in the posterior roots, the end attached to the 

 cord undergoes degeneration, and the peripheral end, the 

 one to which the ganglion is attached, preserves its normal 

 histological characters. From these experiments, which have 

 been confirmed and somewhat extended by Bernard, 9 it is 

 concluded that the ganglia of the posterior roots have an in- 

 fluence over the nutrition of the sensitive nerves, in the same 

 way as the centres influence the nutrition of the motor 

 nerves which emanate from them. These points are- inter- 

 esting, as showing the existence of centres attached to the 

 sensory system of nerves, which have, as far as we know, 

 a purely trophic influence over tho nerves, while the active 

 centres to which the motor nerves are attached regulate, to 

 a certain extent, the nutrition of the nerves, and also are 

 capable of generating nerve-force. We do not know that the 

 ganglia of the roots of sensitive nerves have any function 

 except as trophic centres. 



Properties of the Anterior Roots of the Spinal Nerves. 

 The same experiments that demonstrated that the posterior 

 roots of the spinal nerves are sensitive showed that the ante- 

 rior roots are motor. If the two roots be exposed in an 



1 WALLER, Comptes rendus, Paris, 1857, tome xliv., p. 168. 



2 BERNARD, Lemons sur la physiologic et la pathologic du systeme nerveux, 

 faris, 1858, tome i., p. 235, et seg. 



