school children cannot, therefore, be too
strongly emphasized. The deafness or partial deafness that comes from
this catarrhal infection can seldom be cured; it must be prevented by
the early treatment of the troubles which cause it.

SUMMARY. The mind is closely related to the body. Especially is it
dependent upon the brain, nerves, and sense organs. The sense organs
are special adaptations of the nerve-ends for receiving impressions.
Each sense organ receives only its particular type of impression.

The main visual phenomena are those of color-mixture, after-images,
adaptation, and contrast. Since sensation is the basis of mental
life, defects of the sense organs are serious handicaps and should
be corrected if possible. Visual defects are usually due to a
misshapen eyeball and can be corrected by proper glasses, which
should be fitted by an oculist. Hearing defects usually arise from
catarrhal trouble in the middle ear.

CLASS EXERCISES

1. Make a study of the relation of the mind to the body. Enumerate the
different lines of evidence which you may find indicating their close
relationship.

2. Can you find any evidence tending to show that the mind is
independent of the body?

3. _Color-Mixture._ Colored disks can be procured from C. H. Stoelting
Company, Chicago. If a small motor is available, the disks can be
rotated on the motor and the colors mixed. Mix pairs of complementary
colors, also pairs of non-complementary colors, and note the result. A
simple device can be made for mixing colors, as follows: On a board
stand a pane of glass. On one side of the glass put a colored paper and
on the other side of the glass put a different color. By looking through
the glass you can see one color through transmitted light and the other
color through reflected light. By inclining the glass at different
angles you can get different proportions of the mixture, now more of one
color, now more of the other.

4. _Negative After-Images._ Cut out pieces of colored paper a half inch
square. Put one of these on a white background on the table. With elbows
on the table, hold the head in the hands and gaze at the colored paper
for about a half-minute, then blow the paper away and continue to gaze
at the white background. Note the color that appears. Use different
colors and tabulate the results. Try projecting the after-images at
different distances. Project the after-images on different colored
papers