l
sunlight, intensified by reflection from snow or white limestone, must
be set down among the locally acting causes. Exposure to cold and wet,
to wet and snow storms, to cold drafts and wet lairs must also be
accepted as causes of conjunctivitis, the general disorder which they
produce affecting the eye, if that happens to be the weakest and most
susceptible organ of the body, or if it has been subjected to any
special local injury, like dust, irritant gases, or excess of light.
Again, external opththalmia is a constant concomitant of inflammation of
the contiguous and continuous mucous membranes, as those of the nose and
throat--hence the red, watery eyes that attend on nasal catarrh, sore
throat, influenza, strangles, nasal glanders, and the like. In such
cases, however, the affection of the eye is subsidiary and is manifestly
overshadowed by the primary and predominating disease.

_Symptoms._--The symptoms are watering of the eye, swollen lids, redness
of the mucous membrane exposed by the separation of the lids--it may be
a mere pink blush with more or less branching redness, or it may be a
deep, dark red, as from effusion of blood--and a bluish opacity of the
cornea, which is normally clear and translucent. Except when resulting
from wounds and actual extravasation of blood, however, the redness is
seen to be superficial, and if the opacity is confined to the edges, and
does not involve the entire cornea, the aqueous humor behind is seen to
be still clear and limpid. The fever is always less severe than in
internal ophthalmia, and runs high only in the worst cases. The eyelids
may be kept closed, the eyeball retracted, and the haw protruded over
one-third or one-half of the ball, but this is due to the pain only and
not to any excessive sensibility to light, as shown by the comparatively
widely dilated pupil. In internal ophthalmia, on the contrary, the
narrow, contracted pupil is the measure of the pain caused by the
falling of light on the inflamed and sensitive optic nerve (retina) and
choroid.

If the affection has resulted from a wound of the cornea, not only is
that the point of greatest opacity, forming a white speck or fleecy
cloud, but too often blood vessels begin to extend from the adjacent
vascular covering of the eye (sclerotic) to the white spot, and that
portion of the cornea is rendered permanently opaque. Again, if the
wound has been severe, though still short of cutting into the anterior
layers