tooth, the hard, shiny surface is left just like a thin shell; and one
day you happen to bite down upon a piece of bone in your food, or try
to crack a nut with your teeth, and "crack" goes this brittle shell of
your hollow tooth.

[Illustration: HEALTHY GUMS MEAN HEALTHY TEETH

If the gums are not kept clean and healthy, the second teeth
that are getting ready to push out the first teeth will not come
in strong and good, nor will the teeth remain good. This picture
shows how the teeth grow. Notice the gaps between the teeth,
where food may lodge.]

Right in the middle of each tooth is a tiny hollow, or cavity, filled
with a soft, living pulp containing one or two very sensitive nerves;
and when the decay has eaten into the tooth far enough to reach this
nerve pulp, it makes it ache, and then you have _toothache_.

The one and only thing that is necessary in order to avoid all this
decay and breaking away of your teeth, and throbbing toothache, is to
keep the surface of your teeth, and particularly the sides where they
are next one another, clean and smooth and unbroken. And all that is
needed to keep your teeth perfectly clean and smooth is to use your
toothbrush thoroughly after every meal and at bedtime; and then, if
there are any little scraps of food between the teeth that have not
been brushed away, to pick them out gently with a quill toothpick, or
take a piece of silk or linen thread, push it up between the teeth,
and gently saw backward and forward until you have cleaned out the
space between the roots. You should take at least three to five
minutes after every meal and before you go to bed at night to brush