536 HANDBOOK OF PHYSIOLOGY. 



therefore, justly attributed the phenomena in Bell's experiments to the 

 loss of sensation in the lips; the animal not being able to feel the food, 

 and, therefore, although it had the power to seize it, not knowing how 

 and where to use that power. 



The fifth nerve has also (c), an intimate connection with muscular 

 movements through the many reflex acts of muscles of which it is the 

 necessary excitant. Hence, when it is divided and can no longer convey 

 impressions to the nervous centres to be thence reflected, the irritation 

 of the conjunctiva produces no closure of the eye, the mechanical irrita- 

 tion of the nose excites no sneezing. 



Through its ciliary branches and the branch which forms the long 

 root of the ciliary or ophthalmic ganglion, it exercises also (d), some 

 influence on the movements of the iris. 



When the trunk of the ophthalmic portion is divided, the pupil be- 

 comes, 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; the same effects are produced by destruction of the 

 superior cervical ganglion of the sympathetic, so that, possibly, they are 

 due to the injury of those filaments of the sympathetic which, after 

 joining the trunk of the fifth, at and beyond the Gasserian ganglion, 

 proceed with the branches of its ophthalmic division to the iris; or, as 

 has been ingeniously suggested, the influence of the fifth nerve on the 

 movements of the iris may be ascribed to the affection of vision in con- 

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

 normal influence of the fifth nerve and ciliary ganglion is disturbed. In 

 such disturbance, increased circulation making the retina more irritable 

 might induce extreme contraction of the iris; or under moderate stimu- 

 lus of light, producing partial blindness, might induce dilatation: but 

 it does not appear why, if this be the true explanation, the iris should in 

 either case be immovable and unaffected by the various degrees of light. 



Trophic influence. Furthermore, the morbid effects which division 

 of the fifth nerve produces in the organs of special sense, make it prob- 

 able that, in the normal state, the fifth nerve exercises some special or 

 trophic influence 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 protection 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 

 inflammatory 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 ir- 



