Eyesight, and how to care for it / edited by George Black.

Date:
[1888]
Catalogue details

Licence: Public Domain Mark

Credit: Eyesight, and how to care for it / edited by George Black. Source: Wellcome Collection.

    50/168 (page 46)
    THE OPHTHALMOSCOPE. WHY does ihc pupil appear black ?'' may seem like a very simple question, but thereby hangs the story of one of the most important discoveries of the 19th century. In the beginning of the last century, a French physiologist, while holding a cat under water in the performance of some experiment, was surprised by seeing the blood-vessels of the retina. As the aqueous humor behind the cornea is nearly pure water, its refraction was neutralized by the flat surface of the water in front of the cornea, and this caused the rays of light reflected from the bottom of the cat's eye to pass out of the pupil divergently, and thus rendered visible the structures from which they proceeded. Though not understood at the time, this incident proved that the interior of the eye was not necessarily, under all conditions, invisible, and gave the first hint of brilliant possibilities, whose promise future develop- ments more than fulfilled. The possibility of so mod- ifying the optical conditions as to render the interior