Sanitation and Hygiene for the Tropics: Book One, Primer of Sanitation for ... by John Woodside Ritchie Margaret Anna Purcell

Author:John Woodside Ritchie , Margaret Anna Purcell
Language: eng
Format: epub
Publisher: World Book Company
Published: 1916-03-25T05:00:00+00:00

If possible, the teacher should secure from the school officials a few pesos to purchase chemicals and other materials for a few simple experiments. It will add to the interest of the work and give the pupils a much better understanding of all their science lessons.

CHAPTER VII

THE DIGESTIVE ORGANS AND DIGESTION

Suppose that you have some bread and meat on your plate. Your muscles, your brain, all the parts of your body need the food to nourish them. You eat the bread and meat. It is now on the way to the brain and muscles. How does it get to them ? How must it be changed before it can be used ? What do we mean when we speak of the digestion of the food? What are the digestive organs and why do we have them? We shaU discuss these questions in this chapter.

Fig, 41. The digesUvE organa. The digestive or-

gans. The principal part of the digestive system is the alimentary canal. This is a long passageway through the body. Its principal divisions are the mouth, throat, esophagus, stomach, small intestine, and large intestine. Other digestive organs 336

are the ieeth^ salivary glands (Fig. 42), liver, and pancreas. This great system of organs fills the greater part of the abdominal cavity, and it is most important to understand their work and how. to care for them.

Digestion. If you put a little salt in water, the salt will dissolve. The salt molecules separate and go out all through the water. You cannot see the salt molecules in the water, because they are so small; but if you taste any part of the water, you will find that the salt is everywhere in the water.

The foods that we eat must be changed before we can use them. The large molecules of which they are composed must be broken up into small molecules, so that the foods can be dissolved. Then they can pass through the walls of the intestine into the blood and can be carried all through the body to the cells. Digestion is the process of breaking up and dissolving the food so that it can he taken into the blood.

The work of the teeth. If you put a large lump of salt in water, it will be a long time before the salt is all dissolved. But if you break the lump of salt into many little pieces, it will dissolve quickly. In the same way, the food is digested much more easily when it is broken into little pieces than when it is in big pieces.

The work of the teeth is to grind or break the food into small pieces so that it will be digested quickly. The front teeth are flat and sharp for biting off the food, and the back teeth are large and strong for grinding it into pieces. While the teeth are grinding the food, the

tongue pushes the food out to the sides of the mouth and holds it between the teeth.

The salivary glands. The saliva is made by the salivary glands.

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