The third box, which we call the abdominal cavity, is separated from the chest by a broad, thin muscle, the diaphragm. The abdomen has a hard floor of bone, but the walls are soft, being made up only of the muscles and the lower ribs. In the abdomen are the stomach and intestines, the liver, kidneys, and other organs of which we shall learn later.
Food is carried from the mouth to the stomach by the muscular tube which passes through the chest just back of the breastbone. This tube is called the esophagus. With the mouth, the stomach, and the bowels, it forms what is called the food canal.
As soon as the food enters the mouth, it begins to turn from solid into liquid form, so that the blood can take it up. We chew the food, so that it may become mixed with the saliva in the mouth; then it is swallowed and goes into the stomach. This is a kind of sack which holds about a quart. Just as saliva is secreted in the mouth and acts upon the food, so in the stomach there is a fluid called the gastric juice, which aids digestion. The gastric juice mixes with the food, dissolves it, and makes it soft, so that it can pass through the lower opening of the stomach into the intestines. Here there are other juices which dissolve still more of the food, until at last it is all liquid and looks like milk.
Now it is taken up by the blood through tiny canals that reach down into the intestines and absorb it. But it is not really a part of the blood yet. It must be changed still further, so the blood carries it to the liver. Here it is made a part of the blood, and is able to nourish all parts of the body.
All the food that cannot be dissolved is indigestible, and the body must get rid of it. Some of it passes off as solid matter, by way of the bowels; some is got rid of through the urine; some goes out with the breath, as we have seen; and a great deal goes off in the perspiration. This is why we need to bathe our bodies and to wash our clothing. The perspiration brings the bad matter to the surface, where it clings to the skin and the clothing until it is removed by washing.
But this series of boxes, which we call the head and trunk of the body, would be very helpless without the legs and arms to carry them about and to wait upon them. Taken all together, the head, trunk, and limbs form the body. The framework, which we call the skeleton, is made up of bones. These bones are like the framework of a house,—they keep the body upright and support the muscles. In young people the bones are soft and elastic. A baby often has falls that would break the bones of a grown person, but the baby’s bones are not broken because they are not yet hardened. This is an advantage, for children get a great many more falls than grown people do, and it would be hard for them if the bones were broken as easily.
But if children’s bones do not break, they bend, and it is easy for them to grow into bad shape. If children do not sit up straight they become round-shouldered, and many children get into the habit of carrying one shoulder higher than the other. Often, too, they are careless about walking and sitting properly.
The Wrong Way to Carry a Baby.
In this country, where nearly all weights are carried on the head, we rarely see a man who does not carry his head and shoulders well. He learns in childhood to keep his shoulders even and to hold his head up. But there is one custom of the country which prevents the people from walking well. This is the practice of carrying little children on the hip. It is bad for the children, as it strains the muscles of the lower part of the back, and bends the soft little bones so that they do not grow straight as they naturally would. It is bad, too, for the person who carries the child. The body is thrown to one side, the weight of the child presses the soft organs of the abdomen downward, and the effect is often serious. It is very bad indeed for one child to carry another this way. Babies should be carried in the arms, as European children are.