440 A MANUAL OF VETERINARY PHYSIOLOGY 



abnormally filled with nuclei, the result of the proliferation of 

 nuclei of the nerve (Fig. 124, II and III). In non-medullated nerve 

 degeneration is represented by the disappearance of the axis 

 cylinder. The nerve above the seat of division, though still in 

 communication with the cell, undergoes a limited degeneration 

 as the result of injury, and even the nerve-cells which are intact 

 undergo temporary atrophic changes in consequence of their 

 axons having been cut. 



By suturing divided nerves union occurs, and though the act 

 of division causes degeneration, yet, when union takes place, 

 regeneration of fibres occurs. A fresh axis cylinder grows 

 through the length of the degenerated nerve, and after some 

 weeks, and often months, motion or sensation is perfectly or 

 imperfectly restored. Sensation is always much later in appear- 

 ing than motion. Even suture of divided nerves is not always 

 necessary for union. It is known clinically that the plantar 

 nerves of the horse will often unite in a few months, in spite of 

 a piece being excised, the portion of nerve above sending down 

 an axis cylinder, which soon finds out its divided portion below. 

 If the gap between the divided ends of a nerve is considerable, a 

 new axis cylinder cannot find its way across. 



Trophic Nerves. — Not only is the nutrition of the nerve itself 

 affected by nerve division, but also the nutrition of those parts 

 supplied by it. Ulceration more or less severe has been known 

 to follow injury of certain nerves. Sloughing of the cornea 

 occurs in animals when the ophthalmic division of the fifth is 

 divided, though this may be due to other causes than loss of 

 trophic influence ; and many are practically acquainted with 

 the sloughing of the entire foot which sometimes, though for- 

 tunately rarely, follows the operation of neurectomy. It appears 

 that nerves influence the nutrition of a part. It is well demon- 

 strated in cases of intense muscular atrophy due to nerve injury, 

 and in the dry papillated condition of the nose of the dog after 

 division of the cervical sympathetic. The existence of special 

 trophic nerves has been denied — i.e., of nerves exclusively 

 devoted to maintaining the nutrition of the part. Sloughing of 

 the hoof a few days after neurectomy is evidence of the existence 

 of some special nutrition having been cut off through division of 

 the afferent fibres. The rapid degeneration of muscle after nerve 

 injury is also suggestive of special trophic nerves ; but, as the 

 matter is still in dispute, no positive statement can at present 

 be made. 



