346 



upon the lens have been ascertained, the details and arrangements of 

 the process itself still require elucidation. 



Cramer removed the eye of a seal immediately after the death of 

 the animal, and exposed a portion of the surface of the vitreous 

 body at the back of the organ. He then introduced the electrodes 

 of an electro-magnetic rotation apparatus iuto the opposite attached 

 margins of the iris. The flame of a candle at the distance of 35 

 centimeters from the cornea was distinctly observed on the vitreous 

 sui'face, with a microscope magnifying 80 diameters. At each 

 passage of the electrical current through the organ, the pupil con- 

 tracted, the image of the flame became broader, less distinct, and 

 less definitely outlined. This eff'ect was visible to the naked eye, 

 and indicated the probability of the form of the lens being altered 

 by the contraction of the muscular structures in the interior of the 

 eye. Cramer ascertained that the iris is at least the principal agent 

 in producing the change ; for when a cataract needle was introduced 

 so as to divide the iris, and produce a complete coloboma, the focus 

 was no longer affected by the electrical current. Cramer also re- 

 moved the cornea, annular ligament, and iris, after which the elec- 

 trical current produced no change in the adjustment ; although the 

 ciliary processes were observed to be put upon the stretch. The 

 lens was also shown by numerous experiments to be incapable of 

 changing its own form. It is not muscular ; for when the recent 

 lens was removed from the eye, and the flame of a candle brought 

 to a focus through it, on a piece of oiled paper, the electrical current 

 produced no change in the adjustment. 



Cramer concludes, in this department of his subject, that the iris 

 and ciliary muscle alter the form of the lens. The ciliary muscle 

 contracting pulls the ciliary processes forward, and so prevents the 

 lens from receding under the pressure of the iris. The latter pro- 

 duces the change in the anterior curvature, by a primary contraction 

 of its circular fibres ; followed up by contraction of its radiating 

 fibres, which, from being curved forwards, become straight, and 

 thus pressing on the marginal portion of the anterior surface of the 

 lens, force the central portion forwards. Cramer's explanation of 

 the action of the iris on the lens is based on Stellwag's recent asser- 

 tion, that the posterior chamber has no existence, but that the iris 

 rests immediately on the front of the lens, the ciliary processes, and 

 the zonule of Zinu, so that it projects Uke a dome into the ante- 



