Now the brain is no exception to this same law. During every moment of consciousness this is in ceaseless activity. The peculiar process of cerebration, whatever that may consist in, is taking place; thought after thought comes forth, with no volition on our part; long trains of meditation come forth unbidden, one after another, from the hidden recesses of the brain; sometimes things supposed to be long since forgotten, which have for years been consigned to the rubbish lumber-heap of dead plans and disappointed expectations, rise up suddenly, like a frightened bird before the hunter. Then, again, the sound of some voice, or the strain of some music long unheard, or the glance of an eye, will call up the memories of some bitter and suffering experience with its ten thousand harrowing associations, which go marching forward and backward through the trackless channels of the brain like a vast army of ghosts. All this when the brain has no set task to perform, no intent purpose to follow out, and the body is at ease; and it is only when the peculiar connection or chain of connection of one brain-cell with another is broken, and consciousness fades away into the dreamless land of perfect sleep, that the brain is at rest. In this state it recuperates its exhausted energy and power, and stores them up for future need. The period of wakefulness is one of constant wear; every thought is generated at the expense of brain-cells, which can be fully re-energized only by periods of properly regulated repose. It not unfrequently happens, however, that sleep is only partial; that the brain still continues in some degree of activity, and when we wake, we have dim memories of sub-conscious thought, which has been moving through the brain. Such rest, for the brain, is imperfect, and we are conscious of the conditions of fatigue, which shows how imperative is the necessity for sound, healthy sleep; and if this is not secured, if the brain, through over-stimulation and thought, is not left to recuperate, its energy becomes rapidly exhausted; debility, disease, and finally, loss of power supervene.