67G 



PHYSIOLOGY. 



APPARENT CONTRADICTION. In demonstrating Bell's law there 

 occasionally are seen results which seem to contradict that law, but 

 instead they really confirm it. It is found that in stimulating the 

 anterior (motor) root with electricity the animal sometimes gives 

 evidences of pain. The same thing may occur also after cutting it 

 in the middle and then stimulating, not the central, but the 

 peripheral stump. Bernard has explained the sensibility of the 

 anterior root by admitting that the recurrent sensitive fibers, which, 

 taking their departure from the posterior roots, run back from the 

 periphery towards the center on the anterior root. If the posterior 

 root be cut near to the spinal cord, sensibility in the corresponding 

 anterior root wholly disappears. 



ABC 



Fig. 272. Diagram of the Roots of a Spinal Nerve, Showing Effect 

 of Section. (LANDOIS.) 



The black represents the degenerated parts. A, Section of the nerve-trunk 

 beyond the ganglion. B, Section of the anterior root. C, Section of the poste- 

 rior root. D, Excision of the ganglion, a, Anterior root, p. Posterior root. 

 g, Ganglion. 



The spinal roots united, those of sensation with those of motion, 

 constitute the mixed spinal nerves. They furnish the different parts 

 of the body in which they are distributed with both sensibility and 

 motion. Consequently the section of many spinal nerves leads to 

 anaesthesia and paralysis of the parts innervated. In the recently 

 cut nerves, the central as well as peripheral stumps are excitable by 

 stimulants, the former causing pain, the latter contractions. 



Ganglion. The posterior root, before joining the anterior, 

 has a ganglion. The function of this ganglion is its trophic influ- 

 ence, discovered by Waller and afterward proved by Bernard and 

 others. When an anterior root is cut the peripheral stump becomes 

 atrophied, whereas the central stump remains entire. The latter 

 retains its vitality, since it is still in connection with its trophic 

 center in the cells of the anterior horn of the gray matter. 



On the contrary, when a posterior root is cut between the spinal 



