Sleep is almost as necessary to life as food. Shakespeare calls it, “Nature’s sweet restorer.” We go to bed at night, tired and worried; but we wake up in the morning vigorous and refreshed, feeling like new men. Nothing so quickly wears out the energy of the body as want of sleep. Those who suffer from insomnia, or chronic sleeplessness, know this only too well. One of the most terrible tortures practiced in China is keeping a man without sleep for several days. The poor wretch generally succumbs and dies after three days of such treatment.
It is not certainly known what exactly sleep is and what is its cause. But one theory is that the physical activities of the waking hours gradually produce poisonous waste matter in the tissues of the body, which affect the brain and eventually induce unconsciousness. During sleep, this excess of the poisonous matter is got rid of, and when the tissues are clear of it, consciousness returns, and we wake up, refreshed and invigorated for the life of another day. Anyway, there is no doubt that sleep is not merely resting. Half-an-hour’s sound sleep will do more to restore energy than hours of mere waking rest. It is not only the muscles but the brain and nervous system, that require rest; and this can be obtained only in sleep.
In sleep, we are unconscious of our surroundings. Our senses are inert. We see, smell, taste, feel nothing, and hear nothing unless the noise is loud enough to wake us. And yet the unconsciousness cannot be complete, for we dream. Dreams are mental images, and they prove that part of the brain is working during sleep.
No hard and fast rule can be laid down as to the amount of sleep people require to keep themselves in health because individuals differ. Some require more, some less. A baby should sleep the greater part of the twenty-four hours. Children require more sleep than adults because they are growing, and growth exhausts the energies. For most grown-up people probably six or seven hours of sleep is sufficient, though some can do with less. Each person must find out how much sleep his system needs, and take as a rule neither more nor less. Too little sleep is, in the long run, injurious; and too much is laziness.
Sleep is poetically called “the brother of death”; and death is spoken of as the last sleep or the long sleep. If death is really asleep, we may hope for an awaking to the day of another life.
“Sleep is a death; O make me try
By sleeping what it is to die.”