NERVE 611 



divided nerve becomes inflamed. But in this case the sen- 

 sibility of the eye is lost, and reflex closure of the eyelids 

 ceases to prevent the entrance of foreign bodies. The 

 animal is no longer aware of the contact of particles of dust 

 or bits of straw or accumulated secretion with the conjunc- 

 tiva, and makes no effort to remove them. The lips, being 

 also without sensation, are hurt by the teeth, particularly as 

 the muscles of mastication on the side of the divided nerve 

 are paralyzed, and decomposed food, collecting in the 

 mouth, and inhaled dust in the nose, will tend still further 

 to irritate the mucous membranes. There is thus no more 

 need to assume the loss of unknown trophic influences in 

 order to explain the occurrence of the ulcerative changes 

 than there is to explain the production of ordinary bed- 

 sores, bunions or corns on parts peculiarly liable to pressure. 

 And, as a matter of fact, if the eye be 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 the 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 completely closed ; inflammation came on, and 

 vision was soon permanently lost (Shaw). In another oase 

 a patient lived for seven years with complete paralysis of 

 the fifth nerve, yet the eye remained free from disease and 

 sight was unimpaired (Gowers). 



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

 vagi we have already discussed (p. 221) 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 



