548 THE NERVOUS SYSTEM. 



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 divi- 

 sion to the iris ; or, as Dr. E. Hall ingeniously suggests, 

 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 disturbe'd. In such disturbance, in- 

 creased circulation making the retina more irritable might 

 induce extreme contraction of the iris ; or, under moderate 

 stimulus 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. 



Furthermore, the complete paralysis on division of the 

 fifth nerve, by the morbid effects which it produces in the 

 organs of special sense, makes it probable that, in the nor- 

 mal state, the fifth nerve exercises some indirect influence 

 on all these organs or their functions. Thus, after such 

 complete paralysis, 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 inflam- 

 matory 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 im- 

 paired ; so may the hearing ; and commonly, whenever the 

 fifth nerve is paralysed, the tongue loses the sense of taste 

 in its anterior and lateral parts, i.e., in the portion in 

 which the lingual or gustatory branch of the inferior 

 maxillary division of the fifth is distributed.* 



* That complete paralysis of the fifth nerve may, however, be unac- 

 companied, at least, for a considerable period, by injury to the organs 



