Laurence Sham age 12, of Dorchester, Mass., for his question:

What is sleep?

So far, the experts have not solved the mystery of sleep. They do not know for sure what causes it or why it is necessary. They do know, for sure, however, that it is necessary. After several days and night without sleep a human being may die. The mind and body are unable to work properly even after a few nights of broken sleep.

There are several theories about sleep. They all suggest that sleep has something to do with the brain and the nervous system. One theory suggests that there is a wakefulness center in the brain. During the day, this center stays alert to all the events of livings acting and thinking. At night it closes down and these events do not reach the conscious mind.

Another theory suggests that sleep is the result of tired nerves. The nerves are long, sensitive cells which stretch throughout the body like a telephone system. The long threads gather together in trunk lines. The trunk lined connect with the brain or the spinal cord. Together they form the body's communication system.

Every moment of the day the nerves receive countless bits of information. The sense of touch is busy noticing hot and cold, hard and softs, rough and smooth. The ears pick up a multitude of sounds, the eyes photograph myriad scenes.

All this and other information is flashed along the nerves to the brain. The brain sorts the information and, when necessary, makes decisions and gives orders. When you put your hand accidentally on a hot stove it comes off in a flash. The information hots dangers has been sent to the brain decisions made and orders to move have been given without your realizing. The brain may even order a yelp for good measure.

Imagine all the work that goes on in the nervous system every minute you are awake. All this work uses up energy. Waste materials are created in the process., During a busy day the nervous system gets clogged, choked and tired. Fatigue may be a chemical upset in the nervous system.

When this happens, the alert centers of the nervous system simply close down. Impressions from the busy world are shut off. The communication system is taking no more messages today, thank you. You close your eyes and fall asleep.

Eyes, ears and other senses close down entirely. However, an emergency such as cold, fire or a loud noise will alert them and wake you up. Other operations in the body merely slow down. Breathing and the heart beat go can, though more slowly.

While you sleep, the nervous system repairs itself. We do not know how this happens or even what has to be done. But after a good nights sleep the nervous system is refreshed, ready and eager to carry a million messages throughout the body.

So far as we know, sleep seems to be necessary to the nervous system which keeps mind and body working in harmony. Without proper and regular sleep the body breaks down and the mind becomes dull.