4. What is summer rash? Give the treatment.
5. What is "scratches"? Give the treatment.
6. What feeds produce rashes of the skin?
7. What fungus produces an inflammation of the skin in cattle? Give the treatment.
CHAPTER XII
DISEASES OF THE EYE
GENERAL DISCUSSION.—The eye is situated in the orbital cavity, to which it is attached by muscles that rotate it in different directions. The orbit is lined by fibro-fatty tissues that form a cushion for the eye. Anteriorly it is protected by the eyelids, and in birds by a third eyelid that corresponds to the membrana nictitans of quadrupeds. The lachrymal gland which secretes the tears keeps the above parts moist.
The eye is the essential organ of vision. It is formed by a spherical shell which encloses fluid or semisolid parts. The shell is anteriorly made up of a transparent convex membrane, the cornea, while the remainder of its wall is formed by three opaque layers or tunics.
The external tunic is the sclerotic. It is a white, solid membrane, forming about four-fifths of the external shell. Its external face is related to the muscles and fatty cushion. It receives posteriorly, a little lower than its middle portion, the insertion of the optic nerve, which passes through the shell and spreads out to form a very thin membrane, the retina or internal coat.
The retina lines about two-thirds of the posterior portion of the shell of the eye. It is made up of seven layers. The essential layer is named from its appearance, rods and cones.