FACTS ABOUT HIE EYE.

Waikato Times, Volume XVIII, Issue 1544, 27 May 1882, Page 4

FACTS ABOUT HIE EYE.

The eye is preserved in the convenient form of a sphere, or ball, by the simple de\ice of having its interior cavity filled with liquid, which pre\eivfcs the limp and otherwise flexible coats fiom puckering up into any irregularity of shape. It is like a bladder distended witli water, which is fiim and tensr on account of the contained liquid. so shut in by the membianeons wall that it cannot jiossibly escape anywheie fiom the tight giasp in which it is held. There are, however, in the interior of the eye two distinct ehambeis in which the liquid is distributed, one in front and one behind the crystalline lens. The lens hantr. as it were, in the midst of the liquid. The portion which is in front of the lens is a little more than a veiy wciik aqueous solution of salt, and is on that account tcimcd the aqueous humor of the eye. The portion which is behind mot c neaily resembles a solution of white of e«g. On account of this somewhat thicker consistency, it is termed the viti cous, or glass-like humour. Both humours, however, exert very nearly the same influence upon the vibiationsof the light, and the optical part of the eye thus comes to be considered as composed simply of two refracting parts — the denser lens and the thinner humours. The iris is loosely suspended in the aqueous humour in front of the lens, so that it has the water-like liquid bathing both suifaces, and thus enjoys the same ready freedom of movement that it would possess if it were simply immersed in water. The humours ot the eyes are supplementary aids to the image-forming capacities of the lens. But they are only subordinate aids, as their influence in this lenticular is comparatively small. For simplicity's sake, the crystal lens and the associated humours may be looked upon astogcthsr constituting one single lens, and the visual power of the eye in reality depends upon three curved surfaces which arc found m the combination of humours and lens — the fi out surface of the globe or corner, upon which light in the first instance strikesasitentersthc transparent media of the eye, and the front and the back piotuberant surfaces are of the crystalline mass itself The position of the definite image within the eye is determined by the form of these surfaces, taken in connection with the density of the crystalline substance and itsassociated humours. — Edinbuigh Review.