Sleep, however we account for it, is “the resting time of consciousness.”2 To be sure, there is no absolute arrest of brain activity. There is always, even in the soundest sleep, some cerebral activity.3 We dream. We have nightmares. We sometimes work out problems in our sleep which have defied our every waking effort. There is on record one instance of a college student who got up at three o’clock to solve successfully, while sound asleep, a problem he could not work out at all before he went to bed. There is another instance well attested of a British consul in Syria who, after tearing up letter after letter which he wrote to a Lebanon emir, went to sleep in sheer despair, only to find when he awoke in the morning, that he had written an elaborate letter which in every way satisfied the multitudinous demands of Arabic diplomacy insistent to the last on all the niceties of Oriental etiquette.4

Byron was right. Sleep is neither life nor death. It is a world apart.

Consciousness may be suspended. But the cortical centres are frequently as active when we are asleep as when awake. The attention can be maintained with such unbroken steadiness as to awake some persons with the exactness of an alarm clock on the very minute, even though for purposes of deception the hands of the clock may have been set back without their knowledge. The motor centres can be counted on so confidently that they will drive the somnambulist with the accuracy of a trained chauffeur to his appointed destination. Sleep is, therefore, nothing more than a temporary suspension of a portion of the brain’s activity.