They are made of a kind of bone covered with a hard smooth enamel (ĕn ăm´el). If the enamel is broken, the teeth soon decay and ache, for each tooth is furnished with a nerve that very quickly feels pain. CARE OF THE TEETH. Cracking nuts with the teeth, or even biting thread, is apt to break the enamel; and when once broken, you will wish in vain to have it mended. The dentist can fill a hole in the tooth; but he can not cover the tooth with new enamel. Bits of food should be carefully picked from between the teeth with a tooth-pick of quill or wood, never with a pin or other hard and sharp thing which might break the enamel. The teeth must also be well brushed. Nothing but perfect cleanliness will keep them in good order. Always brush them before breakfast. Your breakfast will taste all the better for it. Brush them at night before you go to bed, lest some food should be decaying in your mouth during the night. Take care of these cutters and grinders, that they may not decay, and so be unable to do their work well. THE CHEST AND ABDOMEN. You have learned about the twenty-four little bones in the spine, and the ribs that curve around from the spine to the front, or breast-bone. These bones, with the shoulder-blades and the collar-bones, form a bony case or box. In it are some of the most useful organs of the body. This box is divided across the middle by a strong muscle, so that we may say it is two stories high. The upper room is called the chest; the lower one, the abdomen (ăb dō´mĕn). In the chest, are the heart and the lungs. In the abdomen, are the stomach, the liver, and some other organs. THE STOMACH. The stomach is a strong bag, as wonderful a bag as could be made, you will say, when I tell you what it can do. The outside is made of muscles; the lining prepares a juice called gastric (găs´trĭk) juice, and keeps it always ready for use. Now, what would you think if a man could put into a bag, beef, and apples, and potatoes, and bread and milk, and sugar, and salt, tie up the bag and lay it away on a shelf for a few hours, and then show you that the beef had disappeared, so had the apples, so had the potatoes, the bread and milk, sugar, and salt, and the bag was filled only with a thin, grayish fluid? Would you not call it a magical bag? Now, your stomach and mine are just such magical bags. We put in our breakfasts, dinners, and suppers; and, after a few hours, they are changed. The gastric juice has been mixed with them. The strong muscles that form the outside of the stomach have been squeezing the food, rolling it about, and mixing it together, until it has all been changed to a thin, grayish fluid. HOW DOES ANYBODY KNOW THIS? A soldier was once shot in the side in such a way that when the wound healed, it left an opening with a piece of loose skin over it, like a little door leading into his stomach. A doctor who wished to learn about the stomach, hired him for a servant and used to study him every day.