First, it mixes the food and makes it pass down the tube.
Second, two sets of cells behind the stomach make two liquids and pour them into the intestine. One set of cells is the sweetbread, or pancreas, and its liquid is the pancreatic juice. The other is the liver and its fluid is the bile.
Third, the pancreatic juice makes three changes in food. First, like the mouth, it changes starch to sugar. Second, like the stomach, it makes albumin a liquid. Third, it divides fat into fine drops. These drops then mix with water and do not float on its top.
20. Bile.—The bile is yellow and bitter. It helps the pancreatic juice do its work. It also helps to keep the inside of the intestine clean.
21. Digestion of water and minerals.—Water and the mineral parts of food do not need to be changed at all, but can become part of the blood just as they are. Seeds and husks and tough strings of flesh all pass the length of the intestine and are not changed.
22. How food gets into the blood.—By the time food is half way down the intestine it is mostly liquid and ready to become part of the blood. This liquid soaks through the sides of the intestine and into the blood tubes. At last the food reaches the end of the intestine. Most of its liquid has then soaked into the blood tubes and only some solid waste is left.
23. Work of the liver.—The food is now in the blood, but has not become a part of it. It is carried to the liver. There the liver changes the food to good blood, and then the blood hurries on and feeds the cells of the body. Spoiled food may be swallowed and taken into the blood with the good food. The liver takes out the poisons and sends them back again with the bile. The liver keeps us from getting poisoned.
24. Bad food.—Sometimes the stomach and intestine cannot digest the food. They cannot digest green apples, but they try hard to do so. They stir the apples faster and faster until there is a great pain. Sometimes the stomach throws up the food and then the pain and sickness stop. Spoiled food makes us sick in the same way.
25. Too fast eating.—When the food stays too long in the stomach or intestine it sours, or decays, just as it does outside of the body. This makes us very sick. When we eat too much, or when we do not chew the food to small pieces, the stomach may be a long time in digesting the food. Then it may become sour and make us sick.
26. Biliousness.—When the food is poor or becomes sour, it is poorly digested. Then the liver has more work to do, and does not change the food to blood as it should. It also lets some of the sour poisons pass by it. These poison the whole body and make the head ache. We call this biliousness. The tongue is then covered with a white or yellow coat and the mouth tastes bad. These are signs of sickness. The stomach and liver are out of order.