Here is a picture of the lamprey eel. You see that it has a row of holes on its neck: these are openings that lead to its lungs; there are seven on each side. It is from this that it is sometimes called seven-eyes. Insects have such openings into their lungs. The grasshopper has twenty-four of them, in four rows. So you see that there are different ways of breathing in different animals. They do not all breathe through their mouths and noses, as we do.
The voice.
You see that the chief use of breathing is to air the blood; but it is of use to us in another way. It makes the voice. We could not speak if we did not breathe. The sound of the voice is made in the top of the neck, in what we call Adam’s apple. This is a sort of musical box at the top of the windpipe: in this box there are two flat cords stretching right across it. Now when we speak or sing, the sound is made in this way: the air, coming up out of the lungs, strikes on these cords, and makes them shake or vibrate. It is just as the vibration of the fiddle-string makes a sound when the bow is drawn over it. If you look at an Æolian harp fixed in a window, you can see that the strings are made to quiver by the wind, and this causes the sound. In the same way, the wind that is blown up from your lungs makes the cords in the Adam’s apple vibrate; and the chest may be said to be the bellows of that little musical box or organ that you have in the throat.
The voices of animals.
The purring of the cat.
Many animals have a musical box in the throat similar to ours. The lowing of the cow, the barking of the dog, and the mewing and squalling of the cat are all done in such a box. You perhaps have wondered how the cat purrs. This noise is made in the same box where she does her mewing and squalling; for if you put your finger on her Adam’s apple while she is so quietly purring, you can feel a quivering motion there.
The croaking of the frog.
Fishes, you know, have no voice. They have no musical box. If they had they could not use it, for the only way in which it can be used is to blow air through it. The frog can not use his so long as he is under water; he has to stick his head up out of water when he wants to croak.
Questions.—What do you breathe for? How is the blood in the lungs changed? What would it do if it were not changed? How is death, caused in drowning? How are the heart and lungs situated? Why are the lungs so light? What is said about the lungs of fishes? What is said about the breathing of the lamprey eel? What about the breathing of the grasshopper? How is the breathing of use besides changing the blood? Tell how the voice is made. What is said about the voices of animals? Where is the cat’s purring done? Why do fishes have no musical box? What is said about the croaking of frogs?