"It appears by a simple experiment, for the principle of which we are indebted to Mariotte, that the small portion of the retina corresponding to the entrance of the optic nerve, is incapable of exciting visual sensation though it receive the image of an object. Place the thumbs together at arm's length, shut the left eye and fix the right eye steadily on the left thumb; then the right thumb if moved gradually outwards (so that its image on the retina of course traverses inwards), ceases to be visible in a particular spot, but is again seen beyond it. It will be remembered that the fibrous lamina of the gray nervous layer of the retina is here evolving itself from the nerve, and is not yet invested with the vesicular or other laminæ; a circumstance of great interest in regard to the modus operandi of the constituents of the retina in vision."

—Robert Bentley Todd and William Bowman, The Physiological Anatomy and Physiology of Man, 1850, p. 435

op. cit., p. 238