First Book in Physiology and Hygiene

by John Harvey Kellogg

13. The Joints.—The places where two or more bones are fastened together are called joints. Some joints we can move very freely, as those of the shoulder and the hip. Others have no motion at all, as those of the bones of the skull.

14. Cartilage.—The ends of bones which come together to form a joint are covered with a smooth, tough substance, which protects the bone from wear. This is called gristle or cartilage. You have, no doubt, seen the gristle on the end of a "soup-bone" or on one of the bones of a "joint of beef."

15. The joint contains a fluid to oil it, so that the ends of the bones move upon each other very easily. If the joints were dry, every movement of the body would be very difficult and painful.

16. The bones are held together at the joints by means of strong bands called ligaments.

17. How the Bones are Made.—The bones are not so solid as they seem to be. The outside of most bones is much harder and firmer than the inside. 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.

18. 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.

19. 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. It is this which makes the bones so hard and firm that they do not bend by the weight of the body. When we are young, the bones have less of this bone-earth, and so they bend easily, and readily get out of shape. When we get old, they contain so much bone-earth that they become more brittle, and often break very easily.

20. A person's height depends upon the length of his bones. The use of alcohol and tobacco by a growing boy has a tendency to stunt the growth of his bones, so that they do not develop as they should.

SUMMARY.

1.	There are about two hundred bones in the body.
2.	All together they are called the skeleton.
3.	The skeleton is divided as follows:
a.	The skull.
			{
					Ribs.
					Breast Bone.
b.	The Trunk.				Pelvis.
					Back Bone.
					Collar Bone.
					Shoulder Blade.
			{
					Upper arm-bones.
c.	The Arms.				Lower arm-bones.
					Wrist.
					Hand and fingers.
			{
					Thigh.
					Knee-pan.
d.	The legs.				Lower leg-bones.
					Ankle, including heel-bone.
					Foot and toes.