is called a joint.

6. The tough substance which covers the ends of many bones is called
cartilage or gristle.

7. The joints are enabled to work easily by the aid of a fluid secreted
for that purpose.

8. The ends of the bones are held together in a joint by means of
ligaments.

9. Bones are about two thirds earthy matter and one third animal matter.

10. The use of alcohol and tobacco may prevent proper development of the
bones.

CHAPTER XIX.

HOW TO KEEP THE BONES HEALTHY.

~1. Composition of the Bones.~--Our bones, like the rest of our bodies,
are made of what we eat. If our food does not contain enough of the
substances which are needed to make healthy bone, the bones will become
unhealthy. They may be too soft and become bent or otherwise misshapen.
This is one of the reasons why bread made from the whole grain is so
much more healthful than that made from very fine white flour. In making
fine white flour the miller takes out the very best part of the grain,
just what is needed to make strong and healthy bones. Oatmeal is a very
good food for making healthy bones.

~2. Bones of Children.~--Sometimes little children try to walk before
the bones have become hard enough to support the weight of the body.
This causes the legs to become crooked. In some countries young children
work in factories and at various trades. This is wrong, because it
dwarfs their growth, and makes them puny and sickly.

~3. Improper Positions.~--The bones are so soft and flexible when we
are young that they are very easily bent out of shape if we allow
ourselves to take improper positions in sitting, lying, or standing.
This is the way in which flat and hollow chests, uneven shoulders,
curved spines, and many other deformities are caused.

[Illustration: IMPROPER POSITION.]

~4.~ In sitting, standing, and walking, we should always take care to
keep the shoulders well back and the chest well expanded, so that we may
not grow misshapen and deformed. Many boys and girls have ugly curves in
their backbones which have been caused by sitting at high desks with one
elbow on the desk, thus raising the shoulder of that side so high that
the spine becomes crooked. The illustrations on this and the following
page show good and bad positions and also the effects of bad positions.

[Illustration: PROPER POSITION.]

~5. Seats and Desks.~--The seats and desks of school-children should be
of proper height. The seats should be low e