1. _Sleep involves primarily Loss of Consciousness._--What then, further than this, is sleep? If we observe somewhat closely, and with a view to scientific arrangement, the different aspects or phenomena that present themselves as constituting that state of body and mind which we call sleep, the primary and most obvious fact, I apprehend, is _loss of consciousness_, of _the me_. Not perhaps of all consciousness, for we seem still to exist, but of self-consciousness, of the me as related to time, and place, and external circumstance We _lose ourselves_, as a common but most exact expression describes it. _We are not at the Time aware of this Loss._--Of course, sleep consisting primarily in loss of consciousness, we are not conscious of the fact that we sleep, for this would be a _consciousness_ that we were unconscious. Illustrations of this fact are of frequent occurrence. You are of an evening getting weary over your book. You are vaguely conscious of that weariness, amounting even to drowsiness; you find it difficult to follow the course of thought, or even to keep the line, but have no idea that you are at length actually asleep for the moment, till the sudden fall of the book awakens you. Nay, one who has been vigorously nodding for five minutes will, on recovering himself, stoutly deny that he has really been asleep at all; the truth is, he was not _conscious_ of it; we never are, directly. _This results from what?_--This loss of consciousness results from the inactivity of the bodily senses. It is these that afford us the data for a knowledge of self in relation to external things. In sleep these avenues of communication with the external world are shut up, and we silently drop off, and, as it were, float away from all _conscious_ connection with it. We no longer recognize our relations to time and space, nor even to our own bodies, which, as material, come under those relations; for it is by the senses alone that we get these ideas. So far as consciousness of these relations is concerned, we exist in sleep as in death, out of the laws and limits of time and space, and irrespective of the body and of all material existence. Mental action, however, doubtless goes on, and we are conscious of thought and of the feeling of the moment, but of nothing further. All self-consciousness is gone. _An Affection primarily of the nervous System._--Sleep, then, would seem to be primarily an affection of the nervous system; not of the reproductive--that goes on as usual, and even with increased vigor; nor yet of the muscular--that is still capable of action; but only of the nervous. That gets weary; by continued use, its vital active force is exhausted, it needs rest, becomes inactive, gradually drops off, and so there results this loss of consciousness, of which I have spoken. It is strictly, then, the nervous system, and not the whole body that sleeps.