Page:Popular Science Monthly Volume 20.djvu/479

Rh his apparatus of motion rests and doubtless sleeps while his mental faculties are in full action. It may happen that the development of this habit of separate sleep is carried to such an extent that the several centers of the brain habitually take their rest independently of each other, and at different times. The clerk will doze as he adds up his column of figures; and the copyist will go on transcribing while his centers of thought and imagination sleep. Conversely, the lower and automatic centers of the brain—the senses—may sleep while the higher centers are awake. Much of the so-called "abstraction" and "absence" of mind we notice in ourselves and others is due to this cause. The brain-worker gains credit for being lost in thought when he does not perceive some object which ought to impress him strongly through one or more of the senses; the farmer toiling over his fields, the hunting-man weary with his day's work, the soldier exhausted by the toil of the march, will sleep so far as one set of faculties, or one part or system of the organism, is concerned, while the others are not only active, but so controlled that the subject of this partial sleep may walk or ride or go through evolutions while his mind sleeps. In short, it is possible, and easy, to fall into any habit of this class, and the inevitable consequence will be that only some of the faculties, or parts of the organism, are ready to sleep when night comes round, while those which remain awake will be unrestful and disturb the others so that they can only doze. In this state of matters, dreaming is an unavoidable experience. Meanwhile, the most highly developed and dramatic dreams occur to those whose sleep is so partial that part only—and, as it would often seem, a small part—of the brain sleeps at any time; or, perhaps, I ought to say, at night—because it not unfrequently happens that those who dream much by night do not dream when they sleep by day. This variety of partial sleep, which tends to sever the natural connections between the several component parts of the mind, is injurious, and therefore it is, as I have remarked incidentally above, that great dreamers are, as a rule, unhealthy. It is easy to see how this must be. If the intellectual faculties are, so to say, broken up in such a way that when some are active the others are sleeping, the checks and restraints which the several parts of the mind naturally impose on each other are wanting, and any one of the faculties may become exaggerated in the exercise of its functions. The practice of dreaming will then extend to the day, and the mind may—especially if there be any inherited and constitutional lack of cohesion among the intellectual faculties—become disorganized. This is a contingency, or more than a contingency let us say, a probability—against which the dreamer of particularly "worked-up" or realistic and elaborate dreams should be on his guard. It does not, however, follow from what I have said that the most coherent dreams are the worst, because the judgment may be simply dozing, and able to correct the scene or story as it passes through the mind. In that case, the