contain the most lime, and that the younger the child the less lime is there in his bones.

It appears that the proportion of lime increases from year to year through life, until finally the entire system. of bones becomes too brittle to make it safe for aged people to risk even so small a thing as a tumble on the sidewalk. Many an older bone has snapped off short where a younger bone would have saved itself by bending a trifle.

This brings us back to the subject of the reason why children have the power to influence the shape of their bones while they are young. The animal part not only prevents bones from being brittle, but it keeps them pliable.

TIED IN A

KNOT

After acid has

from it

Knowing this fact, I applied it to the case of a friend of mine. She was getting a hol- taken the lime low chest and I told her how to save herself. "It will be hopeless after you are twenty," I said. "But you are only twelve now. Your bones are still pliable. If you will raise your chest with vigor, fill your lungs with air, hold yourself in this position for three or four seconds at a time and do it many times a day, you will compel your bones to take the shape for which you will be thankful the rest of your life." I suggested that she give special attention to the matter on the way to and from school each day. She liked my scheme so

well and practiced it so faithfully that within a month the curve of her chest had improved.

A BONE CUT

In so far as you can, feel of your own bones and decide for yourself why each has its own particular shape. You will find long bones for legs and arms; flat bones for shoulder blades, breastbone, and hips; curved long bones for the ribs; curved flat bones for the skull; and you will discover that these latter are so closely joined together that your head seems like a solid, single bone. There are queer, jagged bones, one above the other, in a column, for the back, and many small bones of hand and foot deftly held together, each doing its part in stiffening up the body and in making it serviceable to us.

All grown persons have the same number of pieces to the skeleton, but THROUGH LENGTHWISE the names of our two hundred separate The outer layer is com- bones are of no vital importance to us.

substance is a network Still the figure on page 31 gives a few, of canals and spaces; because it seems almost discourteous thus are bones both light to label such useful articles as nothing more than long and short and flat and crooked bones.

and strong

Most important of all, perhaps, is the graceful column

of the spine. Many a man has lived for years without an arm, without a leg, without bones of various sizes and shapes; but no man has ever been able to live for a moment without that pile of thirty-two small bones that holds his head erect, that keeps his ribs in place, and that guards the treasure of his spinal cord.

In this spine each separate vertebra is held to the one above it and to the one below it by muscles and ligaments on each side, and because of their muscles and ligaments these individual vertebræ are no more responsible for the shape they take, or for the twists and curves they join in making when a gymnast bends

his back from side to side, than are the dumb-bells and the pulleys which the same gymnast uses; for the bones of the spine simply rock back and forth upon each other, according as muscles on this side or that give the needed pull.

5

6

8

9

10

12

1

2

Cervical

Thoracic (or Dorsal)

3

Lumbar

4

5

Sacral

A SIDE VIEW OF THE
SPINAL COLUMN

Each group of vertebræ has
its special name

Just here recall a few facts. As we know, young bones are largely cartilage; they take new shapes if they are put under special, oft-repeated

pressure. A child at a school desk easily gets into the habit of sitting with the vertebræ pressed against each other at the same angle every day. Small muscles do the pulling; they grow strong as they are exercised. In the meantime, also, the separate vertebræ are yielding to pressure. On one side they are growing thinner; on the other side, not being pressed upon, they grow thicker. The result is inevitable. Some of the bones of the back will become wedgeshaped; and, sad to say, a back that has developed wedge-shaped vertebræ - vertebræ that have kept their wedge shape until they are hardened for life-can never hope to be straight again.

VERTEBRA SEEN FROM

ABOVE

Certain other bones may, however, be changed by what they are compelled to do. Suppose you decide that you wish those that are larger and rougher. You may travel a straight road to that definite end. Work the muscles which are fastened to these bones; work them hard; be persistent and the result will come. In studying human skeletons it is not difficult to pick out the bones of such persons as did vigorous muscular

VERTEBRA SEEN

FROM THE

SIDE