Sleep

During sleep the sleeper becomes uncon-scioufl unaware, and more or less unrespon­sive to the environment about him. However, this is a relative matter Some senses and some parts of the body remain more alert and more in function than others. For example, a sleeper may sleep through a loud noise but awake at the lightest touch. Again, while the lungs and heart may work more slowly dur­ing sleep, the sweat glands and some parts of the brain and nervous system may become more active. This increased, even though tem­porary, activity of the nervous system is the explanation of dreams, sleepwalking 'som­nambulism), and talking in one's sleep. Ex­actly why these events occur to a specific per­son on a given night cannot be explained, but the fact of their occurrence demonstrates that sleep and waking are both part of the same cycle of living It is questionable whether the unconscious mind ever completely rests. Anx­iety, certainly, is one of the great enemies of sleep.

Most of the measurable physiological func­tions of the body are diminished during sleep. The body temperature falls, indicating a gen eral decline in metabolism and a decrease in the tone of muscles. Muscular relaxation is one of the key components of sleep. During sleep also the heart beats more slowly, blood pressure    and    pulse    rate    fall,   breathing is   slower,   and   secretion   from   nearly   all viands diminishes

But sleep is more than a time of rest and relaxation. It is also a time of recuperation and repair, of growth and regrowth. During the normal course of living, cells of the body wear out and must be replaced This regener­ation takes place more rapidly during sleep. It has been shown, for example, that the cells of the skin divide and make new cells about twice as fast during sleep.

The amount of sleep a person needs is therefore influenced by his rate of growth Rapidly growing infants need more sleep than children, children more than adults. Again in old age, when the reparative processes of the body are less active, an increase in sleep may be required. Furthermore during the period of recovery from a debilitating illness or opera­tion (convalescence), and in some stages of pregnancy, added increments of sleep or rest may be essential.