Mother: I think you can understand what I say better if you look closely at this picture. This is very much larger than the ear inside your own head. You will see that there are tiny tunnels running every way, some shaped like loops, and one of them very much like the inside of a shell which winds round and round.
Helen: And are all these little tunnels empty?
Mother: No; they are filled with clear water. If you had a very strong mi´cro-scope you would see some things in the ear which would fill you with wonder. First of all we find a little bag floating in the water, made of fine skin, that just fits into all the loops and tunnels. What do you suppose is in this tiny bag?
Amy: I’m sure I don’t know. Please tell us.
Mother: It is full of water, too, but it takes only a drop to fill it. Though this dainty bag is so small, yet there is room for some little stones in it, which we will call ear-stones. The picture shows the road sound travels, only this is much larger than the ear really is.
Percy: I should think it would get lost before it finds the end of all these winding passages.
Mother: It has no trouble in finding its way, and finding it quickly, too. Suppose we start now from the outside porch again, so you will not forget the road. First, it goes through the ear passage and knocks against the ear-drum. This makes the handle inside strike the drum, and the other end hits the anvil; the anvil makes the stirrup tremble; and as sound passes along, that makes the water with the little ear-stones in it tremble also.
Elmer: But what I want to know is how the sound gets into the brain so the master knows what it has to tell him. I don’t see any use of its going through all those tunnels and staying there.
Mother: You may be sure it does not stay there unless there is something wrong with the ear. One of the wires from your telephone system, which you call nerves, passes through a little hole in the skull, and it spreads out on the inside of the tunnels, and all sounds are carried by these nerves into the brain. As soon as one goes in, the master knows what kind of sound it is.
Amy: I don’t see why it should go through so many tunnels.