170 



PHYSIOLOGY OF NERVE 



[CH. XV. 



FIG. 189. Diagram to illustrate Wallerian degene- 

 ration of nerve-roots. 



sympathetic system with which they communicate. The recurrent 



sensory fibres in this root do not 

 degenerate with the others, but 

 are found degenerated in the 

 part of the anterior root at- 

 tached to the spinal cord. 



Section of the posterior root 

 always produces the same phy- 

 siological effect (loss of sensa- 

 tion) * wherever the section is 

 made, but the degeneration effect 

 is different according as the sec- 

 tion is made on the proximal or 

 distal side of the ganglion. If 

 the section is made beyond the 

 ganglion, the degeneration occurs 

 as shown in C beyond the sec- 

 tion in the peripheral portion of 



the posterior root-fibres ; the anterior root remains intact except for 



the recurrent sensory fibres which it con- 

 tains. If the section is made as in D, 



between the ganglion and the cord, the only 



piece that degenerates is the piece severed 



from the ganglion and running into the 



cord; these fibres may be traced up in the 



posterior column of the spinal cord until 



they terminate in grey matter, which they 



do at different levels. The whole of the 



sensory fibres including the recurrent ones 



which are still attached to the ganglion 



remain histologically healthy. 



The accompanying figure (fig. 190) is one 



of the original illustrations made by Dr 



Waller, and I am indebted to the present 



Dr Waller for permission to reproduce it. 



These facts of degeneration teach us, FlG> th e'~ 



what we also learn from the study of em- 

 bryology, that the nerve-fibres of the an- 

 terior root are connected to the nerve-cells 



within the spinal cord, while the posterior 



root-fibres are connected to the cells of the 



spinal ganglia ; or, to put it another way, the trophic centres which 



roots several days after sec- 

 tion of both roots close to the 

 cord ; the anterior fibres are 

 degenerated ; the posterior, 

 being still in connection with 

 the nerve-cells from which 

 they grew, are normal. 



* In order to obtain any appreciable loss of motion or sensation, it is necessary 

 to divide several roots (anterior or posterior as the case may be) as there is a good 

 deal of overlapping in the peripheral distribution of the fibres, 



