THE NERVOUS SYSTEM. 603 



long root of the ciliary or ophthalmic ganglion, it exercises also some 

 influence on the movements of the iris. When the trunk of the oph- 

 thalmic portion is divided, the pupil becomes, according to Valentin, 

 contracted in men and rabbits, and dilated in cats and dogs; but in all 

 cases, becomes immovable even under all the varieties of the stimulus of 

 light. How the fifth nerve thus affects the iris is unexplained ; it has 

 been ingeniously suggested the influence of the fifth nerve on the move- 

 ments of the iris may be ascribed to the affection of vision in consequence 

 of the disturbed circulation or nutrition in the retina, when the normal 

 influence of the fifth nerve is disturbed. In such disturbance, increased 

 circulation making the retina more irritable might induce extreme con- 

 traction of the iris. 



Trophic influence. The morbid effects which division of the fifth 

 nerve produces in the organs of special sense, make it probable that, in 

 the normal state, the fifth nerve exercises some special or trophic influ- 

 ence on the nutrition of all these organs; although, in part, the effect 

 of the section of the nerve is only indirectly destructive by abolishing 

 sensation, and therefore the natural safeguard which leads to the pro- 

 tection of parts from external injury. Thus, after such division, within 

 a period varying from twenty-four hours to a week, the cornea begins to 

 be opaque; then it grows completely white; a low destructive inflamma- 

 tory process ensues in the conjunctiva, sclerotica, and interior parts of 

 the eye; and within one or a few weeks, the whole eye may be quite 

 disorganized, and the cornea may slough or be penetrated by a large 

 ulcer. The sense of smell (and not merely that of mechanical irritation 

 of the nose), may be at the same time lost or gravely impaired; so may 

 the hearing, and commonly, whenever the fifth nerve is paralyzed, the 

 tongue loses the sense of taste in its anterior and lateral parts, and ac- 

 cording to Gowers in the posterior part as well. 



In relation to Taste. The loss of tactile sensibility as well as the 

 sense of taste, is no doubt due (a) to the lingual branch of the fifth nerve 

 being a nerve of tactile sense, and also because with it runs the chorda 

 tympani, which is one of the nerves of taste; partly, also, it is due (), 

 to the fact that this branch supplies, in the anterior and lateral parts of 

 the tongue, a necessary condition for the proper nutrition of that part ; 

 while (c), it forms also one chief link in the nervous circle for reflex 

 action, in the secretion of saliva. But, deferring this question until 

 the glosso-pharyngeal nerve is to be considered, it may be observed that 

 in some brief time after complete paralysis or division of the fifth nerve, 

 the power of all the organs of the special senses may be lost ; they may 

 lose not merely their sensibility to common impressions, for which they 

 all depend directly on the fifth nerve, but also their sensibility to their 

 several peculiar impressions for the reception and conduction of which 



