CHAPTER XXII

FIVE SETS OF NERVE ENDINGS

If the statue of Liberty at the entrance to New York harbor had a healthy set of neurons supplying her five senses; if these neurons were rich in axons and dendrites from foot to brain; and if, by some accident of shot or shell the foot of that towering goddess should be shattered some day, she might see the thing happen on the instant, but she would feel no touch of pain for a full second afterwards. It would take that much time for the stimulus to travel from foot to head, because the two places are one hundred and eleven feet apart.

Scientists prove this rate of travel by experiments with animals and human beings. They have invented various instruments of different size and shape, each one of which is supplied with a device for keeping records. And through these instruments the fact is made plain that a stimulus from the skin travels to the brain at the rate of from ninety-eight to one hundred and thirty-one feet a second. It goes faster or slower according to the number of transfers that have to be made from neuron to neuron in the relay race upward.

It is through such experiments then that we know where it is that we actually suffer.

A child may say: "My finger hurts. I burned it." A

man may say, “I am suffering frightful pain in this gashed foot of mine," and, if we are ignorant enough, we may believe them both. But a scientist knows better. He assures us that there is no pain whatever in the injured part itself; that every sensation we have, every pain we feel, is simply a proof that a stimulus of some sort has reached the brain from this place or that. He says that, as soon as the stimulus arrives, the

THE STATUE OF LIBERTY

brain cells which receive it are changed a little by it, and that that is what we call sensation. This stimulus may travel from eye or ear or any other starting point.

It is within my brain, then, in the wonderful neurons which make up the gray cortex of the cerebrum, that I not only think but feel. There too I see and hear, taste and smell. For, as the last chapter showed, it is by the five great nerve roads that lead to the brain from eye and ear, from nose, tongue, and skin, that we learn what is going on in the world outside of us.

Our own experience shows us that each sense may serve us separately, or that all may serve us together, thus giving us various sets of side views of the same thing.

At this moment I think of some chocolate creams which I ate last evening; and it takes several senses, working together, to tell me what they were like. Neurons of sight tell me they were small, brown, and almost round. Neurons of touch tell me they were smooth and rather soft. Neurons of taste tell me they were sweet and delicately flavored. And it is the combination of information from these three sets of neurons that gives me my true idea of chocolate creams.

Carry the same notion out in other directions. See for yourself how, throughout an entire day, each sense pieces out the others. Everywhere you will find that the more senses you can bring to bear on any object, the more perfectly will you understand and remember it. So true is this that our thoughts about anything are richer or poorer according as different senses have been allowed to bear on the same subject.

When Laura Bridgman thought of a rose, what did the flower mean to her? Touch reported a cluster of delicate, smooth petals, supported on a round stem that sometimes carried points that pricked her unawares.

But let sight and smell add their reports and give us the rose that we ourselves have in mind. Color is added now, and we see the shadings of the petals, the wonderful tracery, the shadows between them, the green calix, and the sunshine over the whole. And added to all is the fragrance a wave of odor so rare that whenever we see this shade of pink elsewhere our thoughts fly swiftly to the fragrance of the rose.

A flower that reported neither color nor fragrance would not enrich the mind very much.

Always, then, it is the combination of the work of the senses that makes the most complete and lasting impression. And it is fortunate for us that our senses do not need to wait for each other in the work they do for us. At the moment when I see I may also hear, and while I see and hear I may also taste and smell.

Many public lecturers have this fact in mind when they are particularly anxious to hold the attention of their audience. Such a man talked in this town not long ago. His subject was the land of Palestine, and as he talked he used his stereopticon, throwing one beautiful scene after another on the screen. He was compelling our neurons of sight to help our neurons of sound

in understanding his descriptions of the places. The scheme worked well. We not only understood him better as he talked, but the impression made will last longer, for two sets of neurons have it in charge.

A PIECE OF APPARATUS THAT HELPS HEARING

a, the tube; b, the eardrum; c, the ear bones; d, the snail shell;

Good teachers work on the same principle. They use blackboard and illustration cards whenever they can. In teaching others, or in trying to understand and remember on our own behalf, let us not forget that the larger the number of neurons we can force into our