command could have reached the fingers from the brain. The baby would have suffered frightful pain, but he would not have been able to move his fingers back or forth to get out of trouble. His arm muscles would have had to come to the rescue of finger muscles and pull the hand away.

If both roots of that spinal nerve had been cut, the baby would not have felt any pain, neither would he have been able to move his finger. The burning would have gone on just the same, however. This was the case with the man mentioned in the first chapter, who could neither move nor feel. In his case both roots of certain nerves were useless.

The impulse which passes over an axon is always truthful if that axon is uncut and uninjured from end to end. But if damage has been done, strange reports may reach the brain. Old soldiers testify to this. One of these men lives near my home, and when we met the other day, he said: "Isn't it strange, my leg was cut off over ten years ago, but last night the heel of that foot itched and pained me so that I thought I should go crazy." "What did you do?" I asked. “Put a hotwater bag against the stump, warmed the thing up, and finally got relief." Of course he knew, as well as I did, that something was irritating the live ends of the axons that used to send reports from the heel to the brain, and that when the cells up there received the stimulus

they had no way of knowing that the axons had been cut in two, and that their extreme ends were no lower down than the knee.

The thinking and seeing part of my friend's brain did certainly tell him the truth. He knew that there was no heel there. Nevertheless, even that knowledge could not change the reports which faithful axons were bound to send to headquarters in the brain.

Something was out of order in their neighborhood, and they clamored for help until it came in the shape of a hot-water bag.

From all this it is evident that nerves and brain and muscles are pretty closely connected. But future chapters will show that the connection is even more intimate than we have yet imagined.

CHAPTER XII

NEURONS THAT LEARN LESSONS

As a child I had learned to swim soon after I learned to walk. Then, for years, there had been no swimming; but the chance came again and I had quite an experience. My bathing suit was on, my oiled cap in place, and I was ready to step down into the Mediterranean Sea from the narrow platform of a bath house at Leghorn; but, no matter how hard I tried, I could not remember just how the swimming was done. Should I strike out with one arm first and then with the other, or with both arms at once? Were the feet to start work at the same time? If so, how were they to go? What was to keep my head up? How in the world was I to keep myself from sinking?

All these questions came and went unanswered. Nevertheless my friends were growing impatient; I must join them at once. Slowly, therefore, I went down the steps into the water. Courage oozed away with every step, but there was no escape. At last I was far enough down to venture. I bent forward a trifle, stretched out my arms, felt the ripples go over my body,

dared to draw up one foot, then the other, and in an instant everything was working in proper fashion. I was swimming out from under the canvas side of my bath house to join my friends swimming as easily and as naturally as if I had been doing it every day for years.

The question just here is, How did it happen that I was able to swim like a fish after I reached the water, whereas before I went into it, I could not give myself so much as a hint about the way to do it?

Many think that the answer to the question lies in the power of the unpretentious cerebellum. They say that my cerebellum saved my swimming reputation.

A famous scientist named Flourens once noticed that although a pigeon with a useless cerebellum does not suffer pain, it does, nevertheless, have the greatest difficulty in standing and in moving about. He saw that, when it moves, the muscles do not pull together in orderly fashion, but rather in an independent, helterskelter way, each muscle, as it were, pulling for itself without reference to any other muscle, so that instead of walking, the poor bird turns one somersault after another in rapid succession.

Dr. Flourens also noticed that the less the cerebellum is injured, the less the pigeon is troubled with these disorderly movements, although even then it walks in a staggering, drunken way. It appears, however, that such pigeons may slowly learn to control their muscles

again, and that after a while they are able to walk and even to fly once more; but they never do it so well as before.

From these and other facts which they have gathered, men who study the subject conclude that the cerebellum is an enormous help to the cerebrum in the matter of

controlling such muscles as we are

c able to guide by our own will power.

-D

-E

They say that while the cerebrum is the commanding general of the nervous

system, the cerebellum is the chief of staff the one that helps take charge of numberless move

ments which we

have learned to make through per

sistent, diligent practice. When we were babies and learned to walk, we thought about each step as we took it. If our minds were diverted, if certain special thinking neurons stopped attending to our footsteps, we tumbled down instantly. For weeks, and even for months, we hardly dared to walk alone.