OH. XV.] 



WALLKR1AN DEGENERATION. 



171 



A represents a section of the mixed nerve beyond the union 

 of the roots ; the whole nerve beyond the section degenerates, 

 and is shaded black. 



B represents the result of section of the anterior root ; only 

 the anterior root-fibres degenerate ; * the sensory fibres of the 

 posterior root remain intact. The small medullated nerve-fibres 

 (not shown in the diagram) also degenerate as far as the ganglion 

 cells of the 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 attached 

 to the spinal cord. 



Section of the posterior root always 

 produces the same physiological effect 

 (loss of sensation) * wherever the section 

 is made, but the degeneration effect is 

 different according as the section is 

 made on the proximal or distal side of 

 the ganglion. If the section is made 

 beyond the ganglion, the degenera- 

 tion occurs as shown in C beyond 

 the section in the peripheral portion 

 of the posterior root-fibres ; the anterior 

 root remains intact except for the re- 

 current 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. 183) is one of the original 

 illustrations made by Dr. Waller, and not published until the 

 publication of his son's text-book quite recently. I am indebted 

 to the present Dr. Waller for permission to reproduce it. 



These facts of degeneration teach us, what we also learn 



Fig. 183. Groups of fibres from 

 the anterior and posterior 

 rm>ts several days after sec- 

 tion of both mots 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 sensation, it is necessary to 

 divide several posterior roots, as there is a good deal of overlapping in t lie- 

 peripheral distribution of the fibres. 



