CHAPTER I.
WHAT SLEEP IS.
Sleep is necessary to the health of the human organism. The Mechanism of Man depends for its sustainment and reparation upon recurring seasons of rest.
The condition of sleep is probably a requirement of organic structure. So far as we can trace it, all animal life sleeps. There is almost conclusive evidence that vegetable life sleeps also.
In this respect organic structure differs from inorganic structure. Minerals do not sleep. Only things that have life sleep. Wheresoever life is there is probably (it is not proved) a conscious individuality that “goes to sleep.” As sleep seems, so far as we can trace it, to be an attendant upon consciousness, a requirement, in fact, of nerve structure, the sleep of vegetable life would appear to indicate the presence of consciousness.
But sleep is not a suspension of vital action. The processes conducted by the vital force continue their work in sleep often more vigorously. The intelligence, also, is not wholly suspended in sleep. The functions of nutrition are performed even more perfectly than in the waking state. Rest appears to be required mainly for the muscular structure and for the nerve system that moves the muscles. The senses are often wholly, always partially, sealed in sleep. But it is doubtful if this be the result of a requirement for rest by the senses. The more probable inference is that the suspension of the senses is necessary to the suspension of muscular action.
Sleep, therefore, may be defined in general terms as the suspension, more or less perfect, of the action of the external senses, so that they cease to convey vividly to the mind the impressions made upon them. The action of the Will is likewise suspended, so that it ceases to convey the commands of the mind to the body. Thus is the rest procured that is required for the body.
The entire mechanism of the body and mind does not sleep, but only a part of it. In sleep the body performs all functions necessary for its continued healthy being. The mind dreams. The consciousness of the Individual Self is awake, for we note our dreams as they occur, believe that we are acting them and remember them afterwards.