Without doubt, this great temperance movement of the railroad men had much to do in helping on the national vote for prohibition in America, which was described in the twenty-eighth chapter. Evidently, both for the nation and for the railroad company, going without alcohol was decided on simply as a good, common-sense, business investment. In other words, sensible men saw that alcohol damaged their nervous systems and made them less efficient. They therefore used their brains, saw what should be done, and did it. The nervous system with the brain is, in point of fact, the center of all bodily activity, all thought, and all sensation. We now turn to the study of it. CHAPTER XXXIV NERVES THAT UNITE MUSCLE AND BRAIN If a cat felt no unpleasant sensation when he needed food, he would never bestir himself from a comfortable nap for the sake of eating. If a mouse felt no unpleasant sensation when the claws of a hungry cat were hooked into his skin to seize him, he might allow himself to be caught and eaten without a struggle. If human beings felt no discomfort in the coldest weather, they might carelessly let themselves be frozen to death. So it is on every side. All along the way we go, our sensations are our best protectors. Indeed, during each day of our lives our animal kindred and we ourselves travel through life over a road that is guarded on either side by what might seem to be a hedge of nerve warnings called sensations. The sensations themselves are of many kinds hunger and thirst, cold and heat, headache, toothache, stomach ache—ills of a thousand different sorts. But through each separate one we learn at last that by giving heed to our sensations to those that are disagreeable as well as to those that are agreeablewe do much to preserve our health and to make the pathway of life delightful. Before the microscope was invented even the wisest men were obliged to do much of their scientific work by guessing. They first imagined that each nerve was a tube filled with something exceedingly fine and delicate, called animal spirits. The stuff, they said, was neither gas nor air, but something far more subtle than either. They thought that by means of this substance every nervous system did its feeling, moving, and thinking. Later, other men supposed that the contents of the nerve tubes was something heavier than gas, and they called it nerve juice. In recent times, however, the microscope has done as much for nerves as for microbes. It has destroyed numberless old-fashioned theories, and has shown that nerves are not tubes at all, but that they are a system of fine fibers which carry stimuli and messages back and forth between the body and the brain. These fibers look like slender threads. They run from the brain to the spinal cord, from the cord to the muscles, then from the muscles up again to the spinal cord and the brain. Just under the skin these fibers cover the body in a close network, and it is through their aid that living beings think and feel and move. More than this, it is well to know that nerve fibers are divided into two groups which do two kinds of work. One group carries stimuli to the brain from skin, eye, ear, nose, tongue, and from all the internal organs of the body. The other group carries commands from the brain to every point in the body that needs directing. When a baby sees a flame, laughs with joy, thrusts his fingers into it, and pulls them out again with a scream, several sets of fibers have been at work: 1. One set, from the eyes, compelled the brain to see a lovely color. 2. Another set brought word from brain to hand muscles, "Feel of it." 3. A third set carried a stimulus to the brain, which seemed to say, "Something dreadful is happening to the fingers." 4. A fourth set brought the prompt command, "Pull the fingers out of the color as fast as possible." In the meantime other groups of fibers set other muscles to work, so that at one point the baby opened its mouth to laugh with joy, and a moment later opened it again to scream with pain. Still other fibers commanded the heart to pump faster and send more blood to the excited head. They commanded the tear glands tó manufacture salt water with incredible speed and in great abundance. They set lungs and vocal cords to work, too. And as the result of so much stimulation sent up to the brain and so many commands sent down from the brain, we end with a nervously exhausted, screaming, red-faced, tear-stained baby, rather a dejected looking living machine. If we could ever follow any series of messages up and down, we should learn to understand how swift their flight is. Stimuli from remote regions of the body fly upward to the brain, and there, in what is really the great central station, the various kinds are recognized and attended to. Commands are issued at once, and each of ONE SET OF FIBERS AT WORK these now goes by its own road downward to the spinal cord. From there it is flashed across an unbroken long ANOTHER SET OF FIBERS AT WORK extended fiber to a toe, or a finger tip, or to any muscle of the body that is to be controlled by it. The longest fibers are those which carry an impulse from the toe up into the backbone, and that bring commands back over the same distance. In a tall man these fibers, carrying messages in one direction or the other, may be four or five feet long. |