CH. LVI.] TROPHIC NERVES. 791 



or whether all nerves in addition to their other functions exercise 

 a trophic influence. 



When a nerve going to an organ is cut, the wasting of the 

 nerve itself beyond the cut constitutes what we have learnt to call 

 Wallerian degeneration, but the wasting process continues beyond 

 the nerve ; the muscles it supplies waste also, and waste much 

 more rapidly than can be explained by simple disuse. The same 

 is seen in the testicle after section of the spermatic cord ; and 

 in the disease of joints called Charcot's disease, the trophic 

 changes are to be explained by disease of the nerves supplying 

 them. 



From these, and numerous other instances that might be given, 

 there is no question that nerves do exert a trophic influence ; 

 the question, however, whether this is due to special nerve-fibres 

 has been chiefly worked out in connection with the fifth cranial 

 nerve. 



After the division of this nerve there is loss of sensation in the 

 corresponding side of the face : the cornea in two or three days 

 begins to get opaque, and this is followed by a slow inflammatory 

 process which may lead to a destruction not only of the cornea, 

 but of the whole eyeball. The same is seen in man ; when the 

 fifth nerve is diseased or pressed upon by a tumour beyond the 

 Gasserian ganglion the result is loss of sensation in the face 

 and conjunctiva, an eruption (herpes) appears on the face, and 

 ulceration of the cornea leading in time to disintegration of the 

 eyeball may occur too. In disease of the spinal ganglia there is 

 a similar herpetic eruption on the skin (shingles). 



In the case of the fifth nerve the evidence that there are 

 special nerve fibres to which these trophic changes are due, is an 

 experiment by Meissner and Biittner, who found that division of 

 the most internal fibres is most potent in producing them. 



Those, however, who do not believe in special trophic nerves, 

 attribute the changes in the eyeball to its loss of sensation. 

 Dust, etc., is not felt by the cornea, it is therefore allowed to 

 accumulate and set up inflammation. This is supported by the 

 fact that if the eyeball is protected by sewing the eyelids together 

 the trophic results do not ensue. On the other hand, in paralysis 

 of the seventh nerve, the eyeball is much more exposed, and yet 

 no trophic disorders follow. 



Others have attributed the change to increased vascularity due 

 to disordered vaso-motor changes : but this is negatived by the 

 fact that in disease of the cervical sympathetic, the disordered 

 vaso-motor phenomena which ensue do not lead to the disorders 

 of nutrition we have described. 



