Dr. Jacob’s account of a membrane in the eye. 301 
membrane, united to it by cellular substance and vessels. This 
structure, not hitherto noticed by anatomists, I first observed 
in the spring of the last year, and have since so frequently 
demonstrated, as to leave no doubt on my mind of its exist- 
ence as a distinct and perfect membrane, apparently of the 
same nature as that which lines serous cavities. I cannot 
describe it better, than by detailing the method to be adopted 
for examining and displaying it. Having procured a human 
eye, within forty-eight hours after death, a thread should be 
passed through the layers of the cornea, by which the eye 
may be secured under water, by attaching it to a piece of 
wax, previously fastened to the bottom of the vessel, the 
posterior half of the sclerotic having been first removed. 
With a pair of dissecting forceps in each hand, the choroid coat 
should be gently torn open and turned down. If the exposed 
surface be now carefully examined, an experienced eye may 
perceive, that this is not the appearance usually presented by 
the retina ; instead of the blue-white reticulated surface of 
that membrane, a uniform villous structure, more or less 
tinged by the black pigment, presents itself. If the extre- 
mity of the ivory handle of a dissecting knife be pushed 
against this surface, a breach is made in it, and a membrane 
of great delicacy may be separated and turned down in folds 
over the choroid coat, presenting the most beautiful specimen 
of a delicate tissue which the human body affords. If a small 
opening be made in the membrane, and the blunt end of a 
probe introduced beneath, it may be separated throughout, 
without being turned down, remaining loose over the retina ; 
in which state if a small particle of paper or globule of air be 
introduced under it, it is raised so as to be seen against the 
