align="left">

If we feel gently at the back of the elbow, rather towards the inner side, we find a thing that feels like a sort of cord, and if we squeeze it or knock it accidentally, we discover that it is what we call the “funny bone.” It is a nerve, and therefore belongs to the most marvelous of all marvelous things. If we take a nerve and look at it, we find that it is just a cord made up of tiny threads which are called fibres. It is these fibres that are the real nerves. The big cord is simply a bundle of them travelling part of their journey in each other’s company.

A nerve-fibre is a thing which is probably not to be found anywhere in the vegetable world, but these things begin to appear quite low in the scale of the animal world, and their importance and number become greater and greater as we ascend. There is no part of the body that does not suffer in some way or another if the nerves running to it be damaged or cut.

When we examine a nerve-fibre, we find that it is a very long thread, usually surrounded by a sheath or coat which contains a quantity of a special kind of fat. There are a great many points of view from which we can think of a nerve as if it were an electrical wire, and the sheath may be regarded as what is called an insulator a thing to prevent the current that flows in the nerve from leaking outside it. It is very interesting to take a modern electrical cable such as men lay in the Atlantic Ocean, and to cut it across and see what it looks like; and then to take a good-sized nerve and cut it across and magnify it so as to compare it with the cut cable. We see at once that men have found it useful to make their cables on exactly the same principle as nerves are made, with bundles of fibres big and little, all carefully insulated from each other. Of course, the nerve is a million times more wonderful, but the general principles of the way in which the nerve-fibres are packed together, and the way in which each is sheathed so as to prevent any leakage of its precious current, are really just the same as in the case of the cable.

When we excite our “funny-bone,” as we call it, by hitting it, we feel a tingling in our fingers. We have excited the fibres which carry feeling along the nerve from the fingers to the brain. In other cases when we excite a nerve, muscles will twitch. We have excited fibres which carry orders along the nerve from the brain to those muscles. This shows that nerves carry something, and may do so in either direction, from the brain, or to the brain. The nerve-fibre is therefore a conductor. It is just like the wires in the cable. They do not make messages, but they carry them. What runs along the wire will run in either direction. It is probable that any particular nerve-fibre carries what it carries only in one direction.

The Living Nerve that Carries Messages Through our Bodies

The wire carries an electrical current. As long as the wire is not broken, and is properly insulated, the current will run. The wire is not alive, and, though we by no means understand what happens in it, yet it has not about it the mystery which we find when we look at a nerve.

For the noteworthy thing about a nerve is that it will only carry what it carries when it is alive. We can remove a piece of nerve from an animal that has been killed, and can study it in various ways. If we keep it moist with water containing a little salt, and if we keep it warm enough, it will live for quite a long time, and as long as it is alive things that disturb one end of it will send something through it. But when it dies it will no more carry messages than a piece of string will. What makes the difference between life and death in the nerve we cannot understand until some day, perhaps, we shall learn what life is. We can see no change under the microscope to account for this difference, for we have to kill the nerve in order to look at it under the microscope.

The Mystery of the Nerve-Current That No Man Can Understand

The thing that runs along the nerve we call a nerve-current, or a nervous current. Current simply means something that runs, and that is really almost all we know about it. It is not the same as anything else in the world; it directly depends upon the life of the nerve, as we have seen. It is not electricity. Curious changes are produced in a nerve when a nerve-current runs along it, and among these changes is the production of electrical currents of various kinds, which have been long and carefully studied. These show that an electrical change has been produced in the nerve when a nerve-current runs along it, and the study of these electrical changes may help us to understand the nerve, but it is a very great and serious mistake to suppose that the nerve-current is electrical.

Electrical currents in a cable or anywhere else move at a wholly different speed from that of a nerve-current. Nerve-currents have been measured again and again, and they travel at rates which, compare with the movement of electricity, are very slow. The rate of a nerve-current seems to be about the same as the rate at which a baseball can be thrown. An electrical current is hundreds of thousands of times faster.

Nothing seems to be used up in a nerve when it conveys a current, any more than in the case of a telegraph wire. So we cannot make a nerve tired. As long as it remains alive, it will go on sending currents as often as we choose to start them in it. The case of a nerve-cell is very different.

The Nerve-Cells upon Which All Our Feelings Depend

We have only been talking about conductors, remember. We have, so to speak, taken a piece of one of these conductors, just as if one took a piece out of a cable, and we have studied that. But if we wished really to understand telegraphy, we should have to study what is at the ends of the cable, and that applies to the case of the nerve too. We found that we could excite a nerve by hitting it against something, as when we hit our funny bone, or by pinching it; and there are dozens of other ways, as, for instance, by giving one end of it an electrical shock, dropping chemicals on it, and so on. But, of course, that is not what happens naturally in our bodies. We must find where the nerve comes from.

Every nerve-fibre grows out of a nerve-cell. It is part of that cell. It is only the servant of the cell, carrying orders from it or messages to it. The real thing, where the greatest mystery lies, and upon which everything depends, is the nerve-cell. When we study the development of the body, we find that every nerve grows out of the cell that it belongs to; we find also that, if a nerve be cut across, the part which is next the cell is unhurt, but the part which is separated from the cell invariably dies. We find also that, if a nerve-cell is destroyed or poisoned, the nerve-fibre running out from it invariably dies, and if the nerve-cell has been actually killed, that nerve-fibre can never recover. So these “cable wires” are not merely alive, but they are created by living cells, of which, indeed, they are living parts. That is one of the marvels which make a cable a very simple thing indeed compared with a nerve.

The Dense Forest of Nerves that Grows Up in Our Body

A nerve-cell may have only one fibre coming from it, or it may have several. Very frequently, for certain purposes, we find nerve-cells which have one fibre coming out from each end of them. The fibres from any nerve-cell are very often found going to meet the fibres from another nerve-cell. Suppose, then, we can trace a nerve fibre from a cell somewhere in the brain, for instance, and we find that it meets another fibre from another cell, perhaps at some other place in the brain. It is interesting to know whether the two fibres run into each other. Careful study shows that the fibres never run into each other. At their extreme ends they break up into tiny little fingers, so to speak, and the fingers of the two fibres will interlace; but they never run into each other. If we study parts of the brain where many nerve-cells and nerve-fibres exist together, we find, as someone has said, that it is very like a dense forest. Their leaves and branches intermingle with each other in the closest possible way; but they never actually join. We shall never find a leaf that belongs to two trees.

What the Simple Brain of a Bee or Wasp is Like

All this is very important, because it teaches us that just as a gas is made of atoms, just as the body as a whole is made of cells, so the nervous system is made up of true units which are also cells, and though these cells are of a very peculiar kind and produce fibres which may run right away from the body of the cell for inches or even feet, yet each cell remains a true unit.

In the very lowest animals that have nerve-cells and nerves, the number is very few, and the arrangement very simple. They are usually arranged merely to carry feeling from the outside of the animal to its inside. But as we ascend the scale, nerve-cells and nerves get more numerous, and often, for convenience, numbers of them get bunched together into little balls, each of which is a sort of nervous centre, perhaps somewhat like a telephone exchange.

When these collections of nerve-cells become very large, they make a thing that we can only call a brain, and such are the brains of a bee or a wasp, for instance. The whole arrangement of nerve-cells and nerve-fibres is called a nervous system.

When the first backbones came into existence, there also came into existence a number of new nerve cells and nerve-fibres, and the central home of this new nervous system was inside the backbone. The old nervous system, such as the insects have, remained, and communications were established between it and the new nervous system.

How the Brain Sends and Receives Messages Through the Nerves

In all animals that have backbones, both these nervous systems are found, and we may say very roughly that while the old one, which is really similar to those found in the days before backbones, looks after the interior life of the body, it is the new nervous system that is the instrument of the mind. At its upper end, the long tube inside the backbone opens out, as we know, into the hollow skull; and in the same way the nervous matter which is found in the backbone, and which we call the spinal cord, becomes enlarged, and forms what we call the brain.

The brain and the spinal cord form what is often called the central nervous system. Through holes in the skull and through openings in the backbone run nerves which connect the central nervous system with every part of the body, and every part of the body with the central nervous system.

It seems quite clear that, whether we take the group of cells that forms a mere hair or any other of the least important parts of the body, we always find that it has a perfect double connection with the central nervous system. The brain, or the spinal cord, or both, can send to it messages upon which its life depends, and it, on the other hand, can send messages to them.

When we come to study the central nervous system, we find it so arranged by means of this double connection that every tiniest part of the body is really in true communication, when necessary, with every part of the body without exception. It is this amazing fact that helps to explain how the body becomes a whole in spite of the infinite variety and number of its parts. In no city on earth, however rich in telephones, and speaking-tubes, and telegraphs, and post-offices, and messenger-boys, is there any arrangement a thousandth part as wonderful as the arrangement by which the nervous system connects all the parts of the city of Mansoul, as John Bunyan called it.

The Forest of Nerves Running to and from Every Part of Our Body

We have already learnt what is necessary regarding nerves. If we simply understand that the lining of the heart, the wall of a vein, the base of a nail, every muscle-fibre, and all other parts of the body are doubly connected by nerves with the central nervous system, we do not need to inquire how and where these nerves run; though, of course, the doctor has to spend long months and years in studying this. We must devote ourselves now to the central nervous system, and especially the brain.

We saw when we were studying alcohol that the central nervous system consists, in a way, of a number of levels, or layers, and that, as the bodies of animals have become more and more wonderful, new layers have been, so to speak, piled up on the older ones, and each new layer is, so to speak, the master of all the layers below it. It is in this way that we can come to understand the working of the brain and the spinal cord. The spinal cord is very old, so to say; its business nowadays is to attend to things which are beneath the notice of the brain, as, for instance, the movements of the stomach and that kind of thing. It is a sort of highly trusted and responsible butler in the house of man, and, like other butlers, it not only looks after a great many small matters on its own account, so as not to trouble the master, but it is also the master’s means of communication. As a rule, the master gives orders to the butler, and then the butler does the rest.

The Spinal Cord that Acts as Butler to the Brain

On the other hand, tradespeople and so forth, when they have anything to say, do not go to the master, but interview the butler, and he takes the message to the master; so also does the spinal cord. When I close my hand, my brain, which gave the order, did not speak directly to the muscles of my hand. No nerve-fibres run directly from my brain to those muscles, but nerve-fibres do run from my brain to the spinal cord, which is my butler. They give orders to certain nerve-cells in the spinal cord, and from those nerve-cells there do run fibres which go to the muscles of my hand. In the same way, when I feel a draught on my skin, the nerves from my skin do not run direct to my brain; they run to cells in the spinal cord, from which communication is made to my brain.

If we cut across the spinal cord, and take a very thin slice of it and stain it with various dyes that will show up the way in which it is made, we find that its structure exactly corresponds with its duties. We find in it fibres and cells. Some of these fibres are running to the brain, some from the brain; a great many of them arise from cells in the spinal cord, and run to other parts of the spinal cord, and end there. If, for a moment, we think of the spinal cord as a huge exchange, or place of business, then these fibres are like the private wires that do not come from, or go to, the outer world, but connect one part of the place of business with another.

The Wonderful Box in which the Central Nervous System is Kept

The usefulness of the spinal cord very largely depends upon the proper working of these beautiful arrangements which keep every part of it informed as to what every other part of it is doing, and enable different parts of it to act in harmony when they so require which is practically always.

The picture shows us the central nervous system as it appears when taken out of the wonderful box the skull and backbone which exists to protect it. We see how, at its upper end, the spinal cord becomes slightly thicker so as to form what we might call a bulb. That, indeed, is one of the names for this part of the brain. It contains the group of nerve-cells which controls our breathing, and the destruction of which means instant death; also another group of nerve-cells which controls the heart; another group which controls the size of the blood-vessels; another for the acts of sucking and swallowing; another which controls perspiration; and there are probably more. All of these are contained in a little portion of nervous tissue that is just about the size of the end of one’s thumb. Above the bulb, things become very complicated. If we had to begin with the study of the grown-up human brain, we should never find the key to it; but if we study the brain as it develops, and if we study the brain in animals, the thing becomes clear. We see quite plainly that what is the lower underneath part of the brain in us, all huddled and squeezed together and completely poked out of sight by something else that has grown over it, is the old brain, the first brain that ever was, so to speak. It contains countless numbers of nerve-cells, arranged in groups with different duties. It is mostly concerned with movements of the body, and in lower animals it is also the place where hearing and seeing and feeling are done. In ourselves we know that some of these senses have become so delicate and wonderful that they require new machinery, and the old centres which were good enough for lower animals are now, in us, only half-way houses towards the new brain.

Behind the old brain there is a large and important piece of nervous tissue which has a name that really means the little brain. It is called the cerebellum. This cerebellum, we have found, gets larger and larger in higher forms of life, but we cannot find that it has anything to do with feeling. We do not hear or see there, it starts no movements, and certainly the will and powers of thinking do not live there. We find that it is a great instrument for making the body do what we want. The power of balancing the body lives there. A drunken man staggers because he has poisoned his cerebellum. Also the balanced use of the muscles for complicated and delicate actions, like painting or playing the violin, depends upon the control of the cerebellum. It may be thought that these duties are not very exalted, and we may wonder, therefore, why the cerebellum should get bigger as we ascend the scale of life. But we have already learnt that the one thing in the world that we can do is to move things, our bodies and things outside them. Through this power of movement, and only through it, our minds can live and act. So it is very important that our control of movement should be as fine as possible.

It can be proved that in the main line of ascent of life, more and more delicacy and accuracy of movement have always appeared. Part of the history of progress is the replacing of strength by skill. Babies and small children are very clumsy, and as they gradually become more skilful, this means mainly that the cerebellum is developing and getting the powers which it has in grown-up people. In proportion to size of the whole body, the clumsy, stupid animals are those that have a very small cerebellum. The best example of this is one of the stupidest of all the higher animals, the hippopotamus. There are three young hippopotamuses at a zoo, as I am writing, and since it was found how small the brain and the cerebellum of the hippopotamus are, I have been carefully studying these young animals. We can understand that when we catch anything, following it with our eyes, and then getting our hands or our mouth to it, we must be using the cerebellum. The hippopotamus has practically no idea of catching at all. It takes a very long time to see even things that it likes, and if they get into a corner, it is so clumsy that it has not sense enough to use either its feet or its mouth to get them out again.

The Little Brain of the Great Hippopotamus

All this depends upon the smallness of its brain, and especially of its cerebellum. It is reckoned that the brain of the hippopotamus weighs about the same as that of the horse, the weight of whose body is only one-fifth as great. It has been proved over and over again that, in the history of life, success has always gone more and more to brains, to skill as against strength, to mind as against muscle. The hippopotamus is a remarkable instance of an animal that has survived through long ages from the days when brains in general were much smaller than they are now, and the explanation is not to be found in its huge size and strength, but entirely in its mode of life. Its size and strength could never have saved it against better brains.

In the past there have been far bigger and stronger animals than even the hippopotamus, and they have all died out, but the hippopotamus is content to live upon grass and similar plants growing in rivers. It has its nostrils right on the very top of its face, so to speak, and so it can lie with its whole body in the water, and just leave its nostrils above to breathe by. In this way it saves itself by hiding, and still lives on, while the other stronger and cleverer animals have completely disappeared from the earth.

As we pass upwards in the scale of life, we find that with the growth of the cerebellum, and the development of skill, there comes a time when even the mouth, that dogs and cats and lions and sealions are so clever in using, is not a good enough instrument for the clever brain.

The Use of the Arms which Gives Man His Great Power

Something even better is required, and so, in the main line of ascent, we find that the animals called lemurs, which are a very humble and ancient kind of monkey, use their hands a little for grasping as well as walking, though they prefer to use their mouths, as anyone can see who feeds them at the Zoo. But when we reach the highest apes, we see that they find and examine, and lift their food with their hands, and then carry it to their mouths. The arms, then, limbs which for countless thousands of years have been used by all sorts of different animals for the same purposes as the hind legs, and for no other, now come to have special purposes of their own, and every finger becomes precious.

Cleverer even than the half-erect apes is man, who, after crawling babyhood is past, frees his fore limbs for ever from the duty of locomotion, and learns how to use every one of his fingers separately, as with the typewriter or the piano. There has therefore been an immense development of skill in man though mere strength has decidedly fallen off and with it there has necessarily gone a great development of the cerebellum.

This is very interesting, because it helps us not only to understand the brain, but also to understand children. Children belong to a race that lives in the world by its cleverness of all kinds, and so they like to practise their skill. This is why children love games of skill, and this especially is why, ever since children existed, they were fond of balls.

Why It is Right that Boys and Girls Should Play

Of course, grown-up people do not like to have their windows broken; but still it is right and natural for children to play. What we call play, and stupidly think of as waste of time, is now known by wise people to be part of the necessary education of a child, if it is to reach the best possible for it in health of mind and body. Its play is really an essential part of the work of the child.

It is a great pity that, though any mother cat may be seen teaching her kittens to play, for she knows how important it is for them to become skilful, many children in our land have nowhere to play but the street, no one to teach them good games, no one to care what becomes of them. And yet, if we are not to care about our children, and therefore the future of mankind, many of us would perhaps not care if the whole earth shot up in flame and vanished this very moment. But we hope that before long all children will be able to have happy playtimes.