8o6 NERVE 



artificially protected, after section of the trigeminal nerve, the 

 ophthalmia either does not occur or is much delayed. 



In man, too, a case has been recorded in which both the fifth and 

 the third nerves were paralyzed. The eye was still shielded by the 

 contraction of the orbicularis oculi supplied by che seventh nerve, as 

 well as by the drooping of the upper eyelid that accompanies paralysis 

 of the third. It remained perfectly sound for many months, till at 

 length the tumour at the base of the brain which had affected the other 

 nerves involved the seventh too. The eye was now no longer com- 

 pletely closed; inflammation came on, and vision was soon permanently 

 lost (Shaw). In another case a patient lived for seven years with 

 complete paralysis of the fifth nerve, yet the eye remained free from 

 disease and sight was unimpaired (Cowers). 



The so-called ' trophic ' effects following division of both vagi we 

 have already discussed (p. 286) so far as they are concerned with the 

 respiratory system. The degenerative changes sometimes seen in the 

 heart are perhaps due to its being overworked in the absence of nervous 

 restraint on its functional activity. The nutritive alterations in 

 muscles and salivary glands after section of motor and secretory nerves 

 seem to depend in part on functional and vaso-motor changes. In the 

 paralyzed muscles nutrition is not only interfered with in consequence 

 of their inactivity, as would be the case even if the paralysis were due 

 to a lesion above the level of the anterior cornual cells, but the already 

 poorly nourished fibres are continually pressed upon by the capillaries, 

 which are dilated owing to the division of the vaso-motor nerves. The 

 degeneration may also be in part ascribed to the loss of a reflex tonic 

 influence exerted on the muscles by the spinal cord, through the 

 ordinary motor nerves (p. 917). When all allowance has been made for 

 these factors, the rapid and characteristic degeneration of the striated 

 muscles, after their connection with the central nervous system is 

 severed, is still inexplicable, except on the assumption that their 

 nutrition is specially related to the integrity of their efferent nerves. 

 In other words, it is necessary to suppose, not, indeed, that distinct 

 trophic nerves exist for the muscles, but that an influence or impulses, 

 which can be termed trophic or nutritive, do normally pass out to them 

 from the spinal cord along their motor nerves. 



Section of the cervical sympathetic in young rabbits and dogs increases 

 the growth of the ear and of the hair on the same side. But it is 

 impossible to separate these consequences from the vaso-motor paral- 

 ysis; and the same is true of the hypertrophy following section of the 

 vaso-motor nerves of the cock's comb and of the nerves of the bones. 

 After section of the superior laryngeal the vocal cord on the side of the 

 section is at once rendered motionless, and remains so, but the muscles, 

 notwithstanding their inaction, do not degenerate. And Mott and 

 Sherrington have found that, although section of the posterior roots in 

 monkeys is followed after a time (three weeks to three months) by 

 ulceration over certain portions of the foot, no corresponding lesions 

 occur in the hand. They believe, therefore, that the lesions are not due 

 to the withdrawal of a reflex trophic tone, but are accidental injuries 

 in positions specially exposed to mechanical or microbic insults. 



One of the best examples of interference with the proper nutrition of 

 a part produced by a lesion in the nerves supplying it is an eruption 

 (herpes zoster), limited to the skin supplied by the nerve-fibres coming 

 from one or more spinal ganglia, and depending on an (infectious) 

 inflammatory change in the ganglia. It has been suggested that the 

 vesicles are formed either because the passage of afferent impulses 

 normally concerned in the nutrition of the skin is interfered with or 



