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I. The various organs of sense require various kinds of stimulation to excite them into action; the particles of light penetrate the cornea and humours of the eye, and then irritate the naked retina; rapid particles, dissolved or diffused in water or saliva, and odorous ones, mixed or combined with the air, irritate the extremities of the nerves of taste and smell; which either penetrate, or are expanded on the membranes of the tongue and nostrils; the auditory nerves are stimulated by the vibrations of the atmosphere communicated by means of the tympanum and of the fluid, whether of air or of water, behind it; and the nerves of touch by the hardness of surrounding bodies, though the cuticle is interposed between these bodies and the medulla of the nerve.
From exposure to cold, or accident or violence, inflammation often spreads on the eye to a considerable degree, the pupil is clouded, and small streaks of blood spread over the opaque cornea. The mode of treatment just described must be pursued. The crystalline lens occasionally becomes opaque. There is cataract. It may be the result of external injury or of internal predisposition.
The eyes are inflamed, and the sight is often obscured by mucus secreted from the eyelids, or by opacity of the cornea. The brain is often affected as early as the second day after the attack; the animal becomes stupid, and his general habits are changed. In this state, if not prevented by loss of strength, he sometimes wanders from his home.
The action of the lens is aided by several refractive media in the eye. These media are the cornea, the aqueous humor, and the vitreous humor. By reason of their shape and density these media refract the rays of light, and bring them to a focus upon the retina, thus aiding in producing a sharp and distinct image of the object.
In cases of considerable increase of tension, particularly if the onset is sudden, the circulation of lymph in the cornea is interfered with, the anterior layers of the cornea become edematous, the spaces between the lamellae filled with albuminous fluid.
He was reputed to be learned, particularly in the modern languages; had a profusion of long, wild hair of a greenish-drab hue, which matched his complexion exactly, this prevalent tint being infused also into the cornea or "white" of his eye, and, in physical proportions, was of weedy and unwholesome growth. He was not a young man of cheerful disposition.
"The barbed formation of the point explains how, under the stroking with the finger, it was forced through the dense tarsal cartilage and against the cornea of the eye." There is a story told in La Medecine Moderne of a seamstress of Berlin who was in the habit of allowing her dog to lick her face.
The growth in the armpits is scant, but is not removed. The iris of the eye is brown often rimmed with a lighter or darker ring. The brown of the iris ranges from nearly black to a soft hazel brown. The cornea is frequently blotched with red or yellow.
The cornea, or parts of it, may become of a deep pink or salmon colour from the formation in it of new blood vessels. The affection may last for from eighteen months to two years. Complete recovery usually takes place, but slight opacities, especially in the site of former salmon patches, may persist, and the disease occasionally relapses.
Benson, Burnett, Demaux, Lawson, Morison, Reuling, Samelson, and others also report congenital deficiency of the irides in both eyes. Jeaffreson describes a female of thirty, living in India, who was affected with complete ossification of the iris. It was immovable and quite beautiful when seen through the transparent cornea; the sight was only slightly impaired. No cause was traceable.
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