llness. The
muscles of the eyes undergo excessive strain in accommodating themselves
to the unnatural position. The battered type, wood-pulp paper, and poor
presswork, now so commonly used in the cheap editions of books and
periodicals, are often injurious to the eyesight.

Reading-matter should not be held nearer to the eyes than is necessary to
make the print appear perfectly sharp and distinct. No print should be
read continuously that cannot be seen clearly at about eighteen inches.
Those who read music are especially liable to strain the eyes, because
exact vision is required to follow the notes. Persons who wear glasses for
reading should be careful to use them while reading music, and good light
is necessary to avoid any undue strain.

After reading steadily for some time, the eyes should be rested by closing
them a short period or by looking at some distant object, even if only for
a few moments. The book, the sewing, and work generally, should be held as
far from the eyes as is compatible with good vision. The natural tendency
is to reverse this rule. We should never read, write, sew, stitch, or
otherwise use the eyes when they smart or tingle, or when the sight is dim
or blurred. The eyes are then tired and need a rest. Much injury may be
done by reading in twilight, or by artificial light in the early morning,
and by reading and working in badly lighted and ill-ventilated rooms.

Good artificial light is much to be preferred to insufficient sunlight.
The artificial light should be sufficiently bright and steady; a fickering
light is always bad. Riding against a strong wind, especially on a
bicycle, may prove hurtful, at least for eyes that are inclined to any
kind of inflammation. The light reflected from snow is a common source of
injury to the eyes. It is a wise caution in passing from a dark room to
avoid looking immediately at the sun, an incandescent light, the
glistening snow, or other bright objects.

The eyes should never be rubbed, or the fingers thrust into them,[46] and
much less when they are irritated by any foreign substance. The sooner the
offending substance is removed the better.

[Illustration: Fig. 137.--Lacrymal Canals, Lacrymal Sac, and Nasal ducts,
opened by their Anterior Portion.]

340. Effect of Alcohol upon the Eye. The earlier and slighter forms
of injury done to the eye by the use of intoxicants are quite familiar:
the watery condition of the eye and of the lids, and the red a