CHAPTER XXXII

.

WHAT SLEEP IS FOR.

[Sidenote: The machinery of the body needs seasons of rest for repairing.]

All animals have their times for sleeping. It would not do for their minds to use the machinery of the body all the time; if they did, the machinery would soon wear out. The brain, and nerves, and muscles, etc., are all repaired during sleep, so that they may be ready for use again.

When you feel tired, it is because your mind has worn the machinery of the body by using it. Now, when you lie down and sleep, the muscles stop working; no messages pass through the nerves, and the brain is at rest, because the mind pretty much stops thinking. But all this time that you sleep the blood keeps circulating, and the breathing goes on. What is this for? It is that the repairing of the machinery may be done, so as to get the brain, and nerves, and muscles ready for the work and the play of to-morrow. The repairing, you know, is all done with the blood. This is the material for repairing as well as for building, and therefore it must be circulating every where while you are asleep, and the breathing must go on to keep the blood in good order.

The repairing of the body is going on all the time while you are awake as well as when you are asleep. But it goes on more briskly when the machinery is not in use than when it is. So we may say that when you are asleep the machinery is lying by for a full repair.

The same is true of the building of the body. More of it is done when you are asleep than when you are awake. You are growing all the time, but you grow most when you are asleep. And it is because the child is growing that he needs more sleep than the adult does. The baby is growing very fast, and so he sleeps a great deal of his time in the day as well as in the night.

[Sidenote: The night the time for sleep.]

The night is given to us as the time to sleep. Then it is dark and still, and we can go to sleep easily. Most animals sleep through the night. You remember that I told you, in