e of adults, because their eyes are still in the course of
development. The eyes, like any other organ which is yet to attain its
full growth, require more care in their use than one which has already
reached its full size. They are peculiarly liable to be affected by
improper or defective light. Hence the care of the eyes during school life
is a matter of the most practical importance.

In no matter of health can the teacher do a more distinct service than in
looking after the eyesight of the pupils. Children suffering from
defective vision are sometimes punished by teachers for supposed
stupidity. Such pupils, as well as the deaf, are peculiarly sensitive to
their defects. Every schoolroom should have plenty of light; it should
come from either side or the rear, and should be regulated with suitable
shades and curtains.

Pupils should not be allowed to form the bad habit of reading with the
book held close to the eyes. The long search on maps for obscure names
printed in letters of bad and trying type should be discouraged. Straining
the eyes in trying to read from slates and blackboards, in the last hour
of the afternoon session, or in cloudy weather, may do a lifelong injury
to the eyesight. Avoid the use, so far as possible, especially in a
defective light, of text-books which are printed on battered type and worn
plates.

The seat and desk of each scholar should be carefully arranged to suit the
eyesight, as well as the bones and muscles. Special pains should be taken
with the near-sighted pupils, and those who return to school after an
attack of scarlet fever, measles, or diphtheria.

Experiment 156. _To test color-blindness._ On no account is the
person being tested to be asked to name a color. In a large class of
students one is pretty sure to find some who are more or less
color-blind. The common defects are for red and green.

Place worsteds on a white background in a good light. Select, as a test
color, a skein of light green color, such as would be obtained by mixing a
pure green with white. Ask the examinee to select and pick out from the
heap all those skeins which appear to him to be of the same color, whether
of lighter or darker shades. A color-blind person will select amongst
others some of the confusion-colors, _e.g._, pink, yellow. A colored plate
showing these should be hung up in the room. Any one who selects all the
greens and no confusion-colors has normal color vision. If, however,