If you look at the backbone of a fish, you can see that it is made up-of many little bones. Your own spine is formed in much the same way, of twenty-four small bones. An elastic cushion of gristle (grĭs´l) fits nicely in between each little bone and the next.
When you bend, these cushions are pressed together on one side and stretched on the other. They settle back into their first shape, as soon as you stand straight again.
If you ever rode in a wheelbarrow, or a cart without springs, you know what a jolting it gave you. These little spring cushions keep you from being shaken even more severely every time you move.
Twenty-four ribs, twelve on each side, curve around from the spine to the front, or breast, bone. ([See page 38.])
They are so covered with flesh that perhaps you can not feel and count them; but they are there.
Then you have two flat shoulder-blades, and two collar-bones that almost meet in front, just where your collar fastens.
Of what are the bones made?
Take two little bones, such as those from the legs or wings of a chicken, put one of them into the fire, when it is not very hot, and leave it there two or three hours. Soak the other bone in some weak muriatic (mū rĭ ăt´ĭk) acid. This acid can be bought of any druggist.
You will have to be careful in taking the bone out of the fire, for it is all ready to break. If you strike it a quick blow, it will crumble to dust. This dust we call lime, and it is very much like the lime from which the mason makes mortar.
