While the mill is grinding the food, there are some factories about the mouth, making and pouring forth a fluid to moisten it. This fluid, called the saliva, is what you feel in the mouth when the mouth waters, as we say. The two largest of these factories are just below your ears. It is these that swell up so much when one has the mumps. These saliva factories do a moderate business generally. Most of the time they only make enough liquid to keep the mouth moist. Sometimes they do not make enough even for this. This is the case when your mouth gets dry, as it is apt to do in fever. When you eat, these factories do a brisk business, for they then have to make a good deal of fluid to mix with the food. It seems as if they knew when it was necessary for them to go to work and make more saliva than usual. This, of course, is not so; but how it is that they are made to work so hard while we are eating we do not know.
The food of plants needs moistening just as our food does. The rain moistens it for the root, the stomach of the plant, so that it may get nourishment from it. When you water the dry earth in a flower-pot, you do for the food of the plant what the saliva factories do for your food.
Parched plants and the parched mouth in fever compared.
Sometimes in fever, as I have just told you, the mouth is very dry. This is partly because the saliva factories have almost stopped work; hardly any saliva comes through their canals into the mouth. It would be hard work then to eat dry food. The dry cracker must be moistened before it can be eaten. This is very much like what sometimes happens to plants when there has been no rain for a long time. There they are, with their roots in the ground, just as they have been all along. The food is close to their little mouths, but it is so dry that they can not well manage it. They languish, therefore, and perhaps wilt. The dry earth is to them like the dry cracker to the fevered mouth.
Questions.—What is done to the food in the stomach? What do the months in the stomach suck up? What is done to the food before it goes into the stomach? What is the use of grinding the food? What harm does it do to eat fast? What is said about the food of plants? What else is done to our food while the teeth are grinding it? Tell about the working of the saliva factories. What is said about moistening the food of plants? How are plants sometimes like persons in a fever?
CHAPTER VI.
MORE ABOUT THE TEETH.
The different kinds of teeth for cutting, and tearing, and grinding.
Notice that in the mill in your mouth there are different kinds of teeth. They are for different purposes. The front teeth are for cutting the food; the large back teeth are for grinding it up fine; the pointed teeth, called the stomach and eye teeth, are for tearing the food.
You can see these different kinds of teeth in different animals. Every animal has such teeth as it needs to divide its food. The dog and the cat eat meat, and they want to tear this to pieces; they therefore have long, sharp, tearing teeth; so, too, have the lion and the tiger, for the same reason. Now look at the cow’s mouth: she has no tearing teeth. The grass that she eats does not need to be torn; it needs to be bruised and ground up, and for this purpose she has large, broad, grinding teeth. These are her back teeth.