700 A MANUAL OF PHYSIOLOGY 



on the side corresponding to the divided nerve becomes inflamed. 

 But in this case the sensibility 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 con- 

 junctiva, 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 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. 236) so far as they are concerned 

 with the respiratory system. The degenerative changes some- 

 times 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 must also be in part 

 ascribed to the loss of a tonic influence exerted on the muscles 

 by the motor cells of the spinal cord, through the ordinary motor 



