10/14 Long bones, like those of the arms and the legs, are hollow. The hollow space is filled with _marrow_, in which are the blood-vessels which nourish the bone. An Experiment.~--If you will weigh a piece of bone, then burn it in the fire for several hours, and then weigh it again, you will find that it has lost about one third of its weight. You will also notice that it has become brittle, and that it seems like chalk. Why the Bones are Brittle.~--The hard, brittle portion of a bone which is left after it has been burned contains a good deal of chalk and other earthy substances, sometimes called bone-earth. |