=14. Too fast eating.=--Some boys fill their mouths with food. Then they cannot chew their food and cannot mix saliva with it. They swallow their food whole, and then their stomachs have to grind it. The saliva cannot mix with the food and so it is too dry in the stomach. Then their stomachs ache, and they are sick. Eating too fast and too much makes children sick oftener than anything else. Birds swallow their food whole, for they have no teeth. Instead, a strong gizzard inside grinds the food. We have no gizzards, and so we must grind our food with our teeth. =15. Teeth.=--We have two kinds of teeth. The front teeth are sharp and cut the food; the back teeth are flat and rough and grind it. If you bite nuts or other hard things you may break off a little piece of a tooth. Then the tooth may decay and ache. After you eat, some food will sometimes stick to the teeth. Then it may decay and make your breath smell bad. After each meal always pick the teeth with a wooden toothpick. Your teeth will also get dirty and become stained unless you clean them. Always brush your teeth with water every morning. This will also keep them from decaying. [Illustration: =Digestive organs of a bird.= _a_ esophagus or swallowing tube. _b_ crop or bag for carrying food. _c_ stomach. _d_ intestine. _e_ gizzard or food grinder.] =16. Swallowing.=--When food has been chewed and mixed with saliva until it is a paste, it is ready to be swallowed. The tongue pushes the food into a bag just back of the mouth. We call the bag the _pharynx_. Then the pharynx squeezes it down a long tube and into the stomach. The nose and windpipe also open into this bag, but both are closed by little doors while we swallow. We cannot breathe while we swallow. If the doors are not shut tightly, some food gets into the windpipe and chokes us. WHAT WE HAVE LEARNED 1. We eat to feed the cells of the body. 2. All food must be made into blood. 3. Changing food to blood is digestion. 4. Cooking softens food and makes it taste good. 5. Food is ground fine in the mouth, and mixed with saliva to form a paste. Some of its starch is changed to sugar. 6. If food is only half chewed the stomach has to grind it. 7. When we swallow, the tongue pushes the food into a bag back of the mouth and the bag squeezes it down a long tube to the stomach. CHAPTER IV DIGESTION IN THE STOMACH =17. The stomach.=--When food is swallowed it goes to the stomach. The stomach is a thin bag. In a man it holds about three pints. Like the mouth, it does three things to the food. [Illustration: =Gastric glands in the stomach (×200).= The cells _a_ and _b_, form the juice. The fibers _c_, bind the tubes in place.] _First_, the stomach gently stirs and mixes the food. _Second_, it pours a fluid over the food. This fluid is called the _gastric juice_. The gastric juice is sour and bitter.