THE FIFTH NERVE. 431 



ducing 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. 



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 

 indirect influence on all these organs or their functions. 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 en- 

 sues 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, i. e., in the por- 

 tion in which the lingual or gustatory branch of the inferior 

 maxillary division of the fifth is distributed. 1 



The loss of the sense of taste is no doubt chiefly due to the 

 lingual branch of the fifth nerve being a nerve of special 

 sense ; partly, also, perhaps, it is due to the fact that this branch 

 supplies, in the anterior and lateral parts of the tongue, a nec- 

 essary condition for the proper nutrition of that part. 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 sen- 

 sibility to the several peculiar impressions for the reception and 

 conduction of which they are purposely constructed and sup- 

 plied with special nerves besides the fifth. The facts observed 

 in these cases 2 can, perhaps, be only explained by the influence 

 which the fifth nerve exercises on the nutritive processes in the 

 organs of the special senses. It is not unreasonable to believe, 

 that, in paralysis of the fifth nerve, their tissues may be the 



1 That complete paralysis of the fifth nerve may, however, be un- 

 accompanied, at least, for a considerable period, by injury to the or- 

 gans of special sense, with the exception of that portion of the tongue 

 which is supplied by its gustatory branch, is well illustrated by a valu- 

 able case lately recorded by Dr. Althaus. 



2 Two of the best cases are published, with analyses of others, by 

 Mr. Dixon, in the Medico-Chirurgical Transactions, vol. xxviii. 



