Читать книгу A monograph on sleep and dream: their physiology and psychology - Edward W. Cox - Страница 6

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Various conjectures have been advanced as to the precise physiological change that attends the condition of sleep. Some have located the source of sleep in the heart and others in the head. It was formerly a favourite theory that the action of the heart slackened and then the blood, flowing slowly through the brain, caused a kind of congestion there. This was, in fact, to look upon sleep as a species of coma that produced unconsciousness by pressure upon the fibres of the brain.

The later and better opinion is, that sleep is produced by the reverse of this process; that it is not a state of congestion but of collapse; that the blood flows from the part of the brain that sleeps, which is thus left in a state of depletion, with a consequent collapse of the brain fibres.

Observation of the actual brain of a man who had been trepanned and over a part of whose brain a movable silver plate was placed entirely confirmed this conjecture. In sleep, the convolutions of his brain were depressed; when awake, they resumed their normal form; when his mind was exerted, they swelled visibly.

Any reader who has been suddenly wakened may recal a sensation as of swelling of the brain by the blood rushing into it. This sensation was probably the result of the rapid erection of the flaccid brain fibres.

Other facts strongly support this theory. When the action of the heart is stimulated by any excitement, mental or bodily, sleep will not come. So long as the brain is busy we court sleep in vain. To induce sleep we apply remedies that tend to draw the blood from the brain to the extremities. A full meal engenders sleep; but not, as formerly supposed, by congesting the brain, but by attracting the blood to the stomach and so depleting the brain. Rapid motion in a cold wind causes drowsiness when warmth is restored. Why? The blood is borne swiftly back to the surface of the body and quits the brain. Many other instances will readily occur to the reader.

Note in another the process of “falling sleep.” The eyes move more and more slowly, the eyelids descend, the head nods and droops, the limbs relax, the book falls from the hand. Usually, before positive sleep occurs, involuntary endeavours at resistance are made. The eyes open with a stare. Consciousness is regained with an effort and a start. The thread of waking thought is resumed. But it is for a moment only. Again the head nods, the eyes blink and close, the limbs relax. He is asleep.

What are our own sensations when we go to sleep? Thought wanders. Ideas come straying into the mind unbidden and with no apparent association. External objects grow dim to the eye and sounds fall faint upon the ear. The communications of the senses to the brain are dull and uncertain. We are conscious that the power of the Will is relaxed. We strive to retain it. We recover it by an effort. We resume the work on which we were engaged. Vain the struggle. The thoughts wander still. The unbidden pictures flit again before the mind’s eye. We are conscious of the relaxation of the limbs and the closing of the eyelids. Then we cease to be conscious of external existence. We sleep.

But we are not conscious of the act of falling asleep—for itself is a suspension of consciousness. With some sleepers sleep is, as they affirm, a condition of entire unconsciousness. These tell us they have no sense of existence until the moment of waking and that, however protracted their slumber, the moment of waking is to them as the moment after having fallen asleep. It is impossible to contradict those who thus affirm, for their mental condition in sleep cannot be read. But if a judgment may be formed from their actions in sleep, as talking and motions of the limbs, the probable explanation will be that they dream but do not remember their dreams. All dreams vanish from their memories as some dreams vanish from the memories of those who habitually dream.

If we observe the aspect of a sleeper, we note the features placid, the breathing regular, the pulse soft and even, the limbs relaxed, the skin moist. Occasionally there are quiverings of the limbs and expressions of the face which betray the presence of mental emotions.

This is the physiological condition of Sleep.

We turn now to its mental condition.