Buckmaster's Elements of animal physiology / by John Angell.

  • Angell, John
Date:
1866
Catalogue details

Licence: Public Domain Mark

Credit: Buckmaster's Elements of animal physiology / by John Angell. Source: Wellcome Collection.

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    of a body depends on the angle of vision. Some persons are unable to recognize certain colours; this defect is termed colour-blindness: its exact cause is unknown. The Aqueous Humour (from L., aqua, water) is the clear limpid fluid which fills the space in the front of the eye between the crystalline lens and the inner surface of the cornea. It consists of 98 per cent, of water and 2 per cent, of solid, chiefly of chloride of sodium (common salt). Its quantity does not in general exceed 4 or 5 drops. When lost by wounds it is quickly replaced; it is most probably secreted by the vessels of the h'is and of the ciliary processes. The Crystalline Lens or Humour in man is a clear, transparent, crystal-like, double convex, circular lens, about i-3rd of an inch in diameter, and I-5 th of an inch in thickness. It lies exactly in the antero-posterior axis of the eye, separating the aqueous from the vitreous humour. It is the most important optical part of the eye. • It is homogeneous to the naked eye, but when boiled or hardened by alcohol, exhibits a peculiar laminated and fibrous structure, very much resembling that of an onion. This lens sometimes becomes white and opaque, producing the disease termed cataract, and consequent blindness. Surgeons partially relieve this blindness by cutting through the coats of the eyeball, and extracting the lens, or by passing a needle through the coats of the eye into the lens, and forcing it down below the pupil, so that it shall no longer obstruct the light. The lens is enclosed in a firm, structureless, brittle, elastic, transparent membrane, termed the capsule of the lens. It is retained in its position by a membrane termed the suspensory ligament of the lens. A circular passage (the catictl of Petit') exists between the margin of the lens and the sus-