immediately after a hard race than to expect to win the race immediately after a hard examination. The second. great lesson of fatigue is: Hard muscular work reduces the power of the brain for a season. Ambitious people often defeat their own plans by being ignorant of these facts about muscle and brain. fatigue. They keep themselves under constant pressure — sit up late at night, sleep too little, waken too early in the morning, and get up tired. It is this sort of overwork, this being too tired, that is dangerous. It results in what we call cumulative fatigue; for the weariness of one day is passed on to the next day, and the outcome of this kind of fatigue stunts growth of body and hinders vigor of mind. We are at liberty to be as tired as we please when we go to bed at night provided we are rested when morning comes. A true scientist not only studies the nervous system as he finds it in human beings to-day but he traces its history from the beginning until now. We, too, are scientists. We, too, intend to do scientific work in this book. The next chapter will, therefore, give us a glimpse at the starting point of that which controls every thought, every act, and every feeling of our lives. CHAPTER VI WHERE THE NERVOUS SYSTEM STARTS From the bottom of some stagnant pool you and I and the scientist might each carry away a cupful of unpleasant-looking sediment. To your eyes and mine it is disagreeable stuff, not worth taking home. To the scientist A LIQUID STOREHOUSE OF TREASURES it is a liquid storehouse of treasures for his mi croscope. But he must hunt for these treasures carefully. He puts a drop of the liquid under the object glass of his microscope. His eye studies it from above, and he sees tiny scraps of things of every form and shape. Part is lifeless matter that never moves — bits of leaves and grass and insect wings that sank to the bottom from the surface of the pool and are decaying now in the water. These he does not care to keep. He also sees active, darting creatures that are as alive as possible. Many of them are microbes of various sorts. They are full of interest to him, but just now he is hunting for something else. At last he finds it, the amoeba - a slow, smooth, glassy-looking object, with an irregular shape. You or I looking at it might mistake this particular amoeba for some lifeless thing. Not so the scientist; he knows the difference. He tells us to look through his microscope and keep an eye fixed on that amoeba until we see something worth reporting; then it is that we make our first discovery. We notice that even while we are watching it the small object with its crooked outline is changing from one shape into another, and it seems remarkable that each shape should be different from the one it had before. The change is in the projections that are poked out from one side or the other like impromptu arms and legs. After sending out each projection the amoeba shifts its position slightly, and it is easy to see that if the shifting creature had a bony body it could not keep up such movements endlessly. In point of fact, it has no bones whatever. Instead, the entire bit of substance is as soft as jelly and almost as transparent. It is called protoplasm - -a word to remember, for protoplasm is an important part of everything that lives upon the earth. Each arm or leg of this bit of living substance which we call amoeba reaches out for no reason that we can discover. Sometimes there may be three projections, at other times a dozen, from the same amœba. One is sent out after the other, but there are no sudden jerks connected with the moving, as is the case when a AN AMOEBA GETTING ITS FOOD AND SWALLOWING IT man strikes out with arms or legs. Instead, each movement is graceful and gentle. At the same time we notice that little by little the amoeba has moved across the glass, and that on the way it even helps itself to food. Watch the longest arm and you will see that the rest of the amoeba gradually flows into it until what was its arm is now its body. Soon a new arm stretches from the body, and into this again all the protoplasm flows, so that at every step there is gain. That is the way the amoeba creeps. More than this, in the progress you notice how it gathers food. As it |