Thropic Symptoms and Disorders. 7 



The degeneration of an active organ applies to the nervous tis- 

 sues themselves. According to the law of Waller, the nerve fibre 

 (axis cylinder), when cut off from its nutritive centre (cell bodj^ 

 with nucleus) degenerates and ultimatel)' perishes. The axis 

 cylinder is a component part of the nenrou, which includes al.so 

 its continuation in the cell and nucleus, and when the latter, 

 which is the source and origin of both nerve impulse and trophic 

 control, is lost, the inactive axis of the nerve fibre degenerates. 

 This law is now availed of in tracing the distribution of nerve fila- 

 ments, the degeneration being found in those that have been cut 

 off from their nerve cells while those that come into the nerve 

 trunk from other sources, distal of the injur}', maintain their 

 integrity. 



In addition to this peripheral atrophy, a degeneration centrad 

 of the injury to the nerve is seen under certain conditions, but 

 especially in intrauterine life. In such cases the atrophy may ex- 

 tend up to and include the central nerve cells, causing a secondary 

 central nervous lesion from an initial peripheral one. 



By bearing these laws of nerve atrophy in mind, lesions that 

 would otherwi.se be obscure, may be satisfactorily accounted for. 



Eruptions and Ulcerations of Nervous Origin. Herpes 

 or shingles in man is now recognized as a nervous disease, cir- 

 cumscribed to the distril:)Ution of given nerves and occurring 

 unilaterally or bilaterally. Deep. seated dermatitis, vesicles, neu- 

 ralgia, pain, itcliing and formication are common accompaniments. 

 The whole is traced to disease of the ganglion on the posterior 

 (superior) root of the spinal nerve distributed to the part. This 

 establishes a principle, and in inscrutable and obstinate, circum- 

 scribed skin disease the veterinarian should see if it coincides 

 with the distribution of one or more sensory spinal nerves. 



Ulcerations are often caused by the lack of protection of a part 

 after paralysis, thus perforation of the cornea will follow .section 

 or disease of the trigeminus These may be prevented by care- 

 fully covering the part, and even cured by a fine protective cover- 

 ing like collodion. 



Alteration of the Secretions often follow on section of the 

 sympathetic trunks, that of tlie cervical sympathetic in rabbits 

 causing excessive congestion of the facial skin, with exudation 

 and scabby product, also profuse secretion of sweat, tears, and ear 

 cerumen and dry, scaly skin. 



