100 SPECIAL SENSES. 



of these nerves. It will be sufficient for our present purposes 

 to state, in a general way, the influence of these nerves upon 

 the movements of the iris. The original observations of di- 

 vision of the sympathetic in the neck, made by Pourfour du 

 Petit, in 1712 and 1725, showed that this operation produced 

 marked and permanent contraction of the pupil. These ex- 

 periments have been repeatedly confirmed, and have been ex- 

 tended by more modern observers to show that, after division 

 of the nerve, galvanization of the superior extremity pro- 

 duces enlargement of the pupil. They have also been re- 

 peated and confirmed by Nuhn J and by Wagner, 2 who oper- 

 ated upon the human subject a short time after decapitation. 



There can be no doubt that the action of the sympathetic 

 upon the pupil is directly antagonistic to that of the third pair, 

 the former presiding over the radiating, or dilating muscular 

 fibres ; and the only question to determine is the course taken 

 -by the sympathetic filaments to the iris. Experiments on 

 the influence of the fifth pair upon the pupil have been some- 

 what contradictory in different animals. In rabbits, section 

 of this nerve in the cranial cavity produces contraction of the 

 pupil ; but in dogs and cats the same operation produces dila- 

 tation. 3 In the human subject, of course, it is impossible to 

 determine this point by direct experiment ; and the varying 

 results obtained in observations upon different animals prob- 

 ably depend upon differences in the anatomical relations of 

 the nerves. 



The experiments of Bonders, made upon rabbits, in which 

 division of the fifth was found to produce contraction of the 

 pupil, show that this influence is derived from connections of 

 the sympathetic with the fifth at or near the ganglion of 

 Gasser. In the first place, it had been shown by Bernard, 

 that contraction of the iris follows division of the fifth, even 



1 NUHN, Zeitschrift fur rationelle Medecin, Heidelberg, 1853, Neue Folge, Bd. 

 iii., S. 135. 



2 WAGNER, Note sur quelques experiences sur lapartie cervicale du nerf grand 

 sympathique, chez une femme decapitee. Journal de la physiologic, Paris, 

 tome iii., p. 175. 3 See vol. iv., Nervous System, p. 194. 



