Fig. 40—Isolated retina, with optic nerve attached.
After the choroid and the sclerotic have been cut away, drop the retina into some water, and it will slowly unfold itself by “ballooning” out into a perfect and beautiful specimen. ([Fig. 40].) But, if it is desired to study the specimen closely, it is better to suspend it in a jar or bottle made of thin glass, and containing a 5 per cent. solution of formaldehyde. Remember that the retina is a delicate membrane in any state; the slightest rough handling may cause it to be torn, or otherwise damaged. If the vessel, in which the specimen has been placed and suspended, has enough preserving fluid to completely fill it, and it is firmly stoppered, the whole thing may be inverted, and turned in any direction, even abruptly, without fear of damaging the retina. This way of keeping the retina will give opportunity to inspect and study the inside as well as the outside of the membrane; the blood-vessels, and other important parts easily recognized.
THE SAGITTAL OR VERTICAL SECTION OF THE EYE
Place an eye in a 5 per cent. solution of formaldehyde for about two weeks. If the eye is kept in that solution longer than that time, the lens is apt to become so hard that in cutting it the capsule and suspensory ligament will be torn, and the lens will then become detached; if for a shorter space of time, the lens and other tissues will be so soft that all may be so badly torn or lacerated, that a perfect specimen will not be possible.
It sometimes happens that in keeping a number of eyes together in a vessel for the purpose of hardening them in the formaldehyde solution, the corneas of some will be crushed in. For this dissection, select an eye that has the cornea in perfect condition.
Remove all the outside tissues with the scissors, being particular to have the region immediately surrounding the optic nerve perfectly clear and clean. If the optic nerve is longer than 5 mm., cut it off to that length.
Fig. 41—Showing the beginning of the cutting of the eye for sagittal sections.
