448 DISSECTION OF THE EYE. 



The retina may be removed without lacerating the tunics of either of the 

 humors ; and the pigmentum nigrum, which often adheres to that part of the 

 vitreous humor which was connected with the ciliary processes, may be washed 

 away with a piece of soft sponge. By this washing, the radiated grooves in the 

 vitreous humor, which were connected with the ciliary processes, will be very 

 apparent. 



To examine the iris in its natural situation, an aperture may be made in the 

 cornea of a fresh eye near its circumference, and the cornea cut out with the 

 strong scissors. This exposes the anterior surface of the iris. 



The iris may then be easily removed, and the crystalline lens, with the cen- 

 tral extremities of the ciliary processes surrounding it, will be exposed to view. 



To examine the ciliary processes on the other side, a lancet may be plunged 

 into another eye, somewhat anterior to the middle, and the eye divided by 

 means of the strong scissors. The anterior section should then be laid on the 

 cornea, and the ciliary process will appear very distinctly, seen through a por- 

 tion of the vitreous humor. The retina may also be seen at the same time, 

 and a judgment may be formed of its extent. The view will be more distinct, 

 if part of the vitreous humor should be cut away with the scissors and forceps, 

 so as to lessen the quantity without deranging the parts under it. 



Several methods have been proposed for rendering the structure of the vitre- 

 ous humor, and the processes of the tunica hyaloidea, more distinct. None of 

 them have been very successful : but, if the vitreous humor be suspended in 

 water by means of a thread passed through that part which surrounds the 

 crystalline lens, and some large incisions be made into the most depending part 

 of it, after some days of suspension its bulk will be diminished, by the discharge 

 of the fluid. If, in this situation, it be immersed in a solution of nitrate of 

 silver, the tunica hyaloidea will become very apparent ; and, by various degrees 

 of exposure to light, may have its color varied from a whitish opacity to a dark 

 brown. 



The appearance of the retina is also much changed by immersion in the solu- 

 tion of nitrate of silver. This effect of the solution, at first sight, appeared 

 calculated to decide the question respecting the extent of the retina ; but, after 

 several applications, it could only be said, that the pulpy substance of the retina 

 appeared to terminate at the commencement of the ciliary processes, while a 

 membrane of a different texture seemed continued from it to the crystalline 

 lens. 



