The human body A beginner's text-book of anatomy, physiology and hygiene .. . crystalline lens, a soft jelly filling up all the back part ofthe cavity of the eyeball. 7. The Use of Aqueous Humor, Lens, and Vitreous Humoris to gather the rays or lines of light which enter the eye,and so bend and direct them, that all those starting fromone point outside the eye meet again in one point on theretina, and excite the same nerve-fibre. This enables usto see things distinctly, because an exact image of thething looked at is made on the retina. In Fig. 56, Oanswers to the lens of the eye; Z>, E^ is
The human body A beginner's text-book of anatomy, physiology and hygiene .. . crystalline lens, a soft jelly filling up all the back part ofthe cavity of the eyeball. 7. The Use of Aqueous Humor, Lens, and Vitreous Humoris to gather the rays or lines of light which enter the eye,and so bend and direct them, that all those starting fromone point outside the eye meet again in one point on theretina, and excite the same nerve-fibre. This enables usto see things distinctly, because an exact image of thething looked at is made on the retina. In Fig. 56, Oanswers to the lens of the eye; Z>, E^ is the object looked 6. How is the interior of the eyeball filled ? Use of these sub-stances ? Their number ? Names ? Describe each. 7. What is the use of aqueous humor, vitreous humor, and lens?How does their action enable us to see distinctly? How is the image IIOPV IMAGES ARE MADE ON THE RETINA. 229 at; and d, e, its image on the retina. The image is muchsmaller than the object, and is wrong side up, but themind has learned by experience to understand it in theright \ Fig. 56—Illustrating the formation behind a convex lens of a diminished andinverted image of an object placed in front of it. 8. Short-Sight and Long-Sight.—When you use a tele-scope or an opera-glass to look at any object, you have tofocus it. The arrangement which will enable you touse it for seeing near objects distinctly, must be changedbefore you can use the glass for seeing things fartheroff. In our eyes, the lens does this focusing; it changesaccording as we look at near or distant things. In per-sons with good eyes [A, Fig. 57), the lens can accuratelyfocus on the retina, images of very distant objects, andalso of things within seven or eight inches of the other persons [B), the eyeball is too long from frontto back, and the lens cannot focus on the retina therays or lines of light coming from distant objects: suchpersons are short-sighted. They can see very distinctlythings near the eye,
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Keywords: ., bookcentury1800, bookdecade1, booksubjectphysiology, bookyear1884
