ACCOMMODATION. 109 



ing perfect, and mentions another case, reported by Yon 

 Graefe, in which accommodation was not disturbed after loss 

 of the entire iris. 1 



We have already noted the fact that the pupil contracts 

 when the eyes are made to converge by the action of the 

 muscles animated by the third pair of nerves ; a and it is evi- 

 dent that convergence of the eyes always occurs in looking 

 at very near objects. It becomes a question, then, whether 

 the contraction of the pupil in accommodation for near ob- 

 jects be associated with the action of the third nerves, or 

 with filaments from the ophthalmic ganglion, which supplies 

 the nervous influence to the ciliary muscle. This seems to 

 have been definitively settled by Bonders, who demonstrated 

 two important points : First, that increased convergence of 

 the visual lines without change of accommodation makes the 

 pupil contract, as is easily proven by simple experiments with 

 prismatic glasses. Second, that when accommodation is ef- 

 fected without converging the visual axes, "each stronger 

 tension is combined with contraction of the pupil." 8 



The action of the iris, as is evident from the facts just 

 stated, is, to a certain extent, under the control of the will ; 

 but it cannot be disassociated, first, from the voluntary action 

 of the muscles which converge the visual axes, and second, 

 from the action of the ciliary muscle. Bonders states that, 

 by alternating the accommodation for a remote and a near 

 object, he could voluntarily contract and dilate the pupil more 

 than thirty times in the minute. 4 Brown-Sequard, in dis- 

 cussing the voluntary movements of the iris, mentions a case 

 in which " the pupil could be contracted or dilated without 

 changing the position of the eye or making an effort of adap- 

 tation for a long or a short distance. 5 



1 HELMHOLTZ, op. cit., p. 151. 2 See vol. iv., Nervous System, p. 134. 



3 BONDERS, Anomalies of Accommodation and Refraction of tJie Eye. The 

 New Sydenham Society, London, 1864, p. 574. 4 Loc. cit. 



5 BROWN-SEQUARD, Recherches experimentales sur Vinftuence excitatrice de la 

 lumiere, du froid et de la chaleur sur Viris. Journal de la physiologic, Paris, 

 1859, tome ii., p. 287, note. 



