814 TROPHIC NERVES [CH. LVII. 



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 such as haemorrhage in 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, and 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 ; against this is 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. Nevertheless in trophic disorders, it is very difficult 

 to be sure that the disordered metabolism is not in part due to 

 vascular disturbances. 



There can, therefore, be but little doubt that we have to deal 

 with the trophic influence of nerves ; * but the dust, etc., which falls 

 on the cornea must be regarded as the exciting cause of the ulceration. 

 The division or disease of the nerve acts as the predisposing cause. 

 The eyeball is more than usually prone to undergo inflammatory 

 changes, with very small provocation. 



The same explanation holds in the case of the influence of the 

 vagi on the lungs. If both these nerves are divided, the animal 

 usually dies within a week or a fortnight from a form of pneumonia 

 called vagus pneumonia, in which gangrene of the lung substance is 

 a marked characteristic. Here the predisposing cause is the division 

 of the trophic fibres in the pneumogastric nerves ; the exciting cause 

 is the entrance of particles of food into the air passages, which on 

 account of the loss of sensation in the larynx and neighbouring parts 

 are not coughed up. Another trophic disturbance that follows 

 division of the vagi is fatty degeneration of the heart. 



Many bedsores are due to prolonged confinement in bed with 

 bad nursing ; these are of slow onset. But there is one class of bed- 

 sores which are acute; these are especially met with in cases of 



* The proof, however, that there are distinct nerve-fibres anatomically is not 

 Very conclusive. 



