THE SPINAL CORD. 389 



the injury is followed by loss of both sensibility and voluntary motion 

 in the corresponding parts. It is also an important fact that, in these 

 instances of section of the trunk, branches, or roots of a spinal nerve, 

 the consequent loss of sensibility or motion is persistent, so long as the 

 injury lasts. The nervous functions are not restored until the divided 

 nerve fibres have gone through with the process of degeneration and 

 regeneration, and have again acquired their natural continuity of text- 

 ure. This shows that the suspension of functional activity is directly 

 due to the injury of the nerve fibres, and not to the sympathetic action 

 of other parts. 



Centripetal and Centrifugal Degeneration of divided Nerve Fibres. 

 The degeneration of nerve fibres in a divided spinal nerve (page 

 353) takes place, below the point of section, throughout the peripheral 

 portion of its trunk and branches, while its central portion, above the 

 point of section, remains unaltered (Fig. 105, A). In this peripheral 

 degeneration, all the fibres of the nerve, both sensitive and motor, are 

 involved ; and it is consequently plain that in both kinds their separa- 

 tion from the nervous centre has produced a disturbance of nutrition 

 resulting in atrophy. Such a degeneration is "centrifugal ;" that is, it 

 affects the nerve fibres from the point of section outward. This ex- 

 pression does not imply a gradual extension of the process in that 

 direction, since we know that in reality (page 354) it advances with 

 the same rapidity throughout; but it indicates the fact that, after 

 division of a spinal nerve, it degenerates between the point of section 

 and the periphery, and not toward the nervous centre. 



If the section be made, not upon the trunk of the nerve, but upon 

 its anterior root above its junction with the posterior root, the same 

 result takes place ; that is, the divided fibres degenerate in a centrifugal 

 direction, while that portion of the nerve root still connected with the 

 spinal cord remains unaltered (Fig. 105, B). But in this case it is only 

 the motor fibres in the nerve trunk which suffer degeneration ; its sensi- 

 tive fibres, derived from the posterior root, are not affected. After 

 such a division, the degenerated motor fibres may be distinguished, in 

 the nerve trunk and branches, from the unaltered sensitive fibres 

 with which they are associated ; and even after its inosculation with 

 other nerves and subsequent ramification, the degenerated fibres belong- 

 ing to the original nerve root may be recognized by their microscopic 

 appearance. The degeneration or immunity of these fibres, therefore, 

 depends on the severance or the preservation of their connection with 

 the spinal cord. 



But if the section be made on the posterior nerve root, between its 

 ganglion and the spinal cord, the effect is reversed (Fig. 105, C). In this 

 instance the portion of nerve root attached to the ganglion remains 

 unaltered ; that which is connected with the cord suffers degeneration, 

 and the degenerated fibres can be traced to their entrance into the gray 

 substance of the posterior horn. This degeneration is therefore " cen- 

 tripetal," since it takes place between the point of section and the spinal 



