Our insensibility to habitual noises, etc., whilst awake, proves that we can neglect to attend to that which we nevertheless feel. Similarly in sleep, we grow inured, and sleep soundly in presence of sensations of sound, cold, contact, etc., which at first prevented our complete repose. We have learned to neglect them whilst asleep as we should whilst awake. The mere _sense-impressions_ are the same when the sleep is deep as when it is light; the difference must lie in a _judgment_ on the part of the apparently slumbering mind that they are not worth noticing. This discrimination is equally shown by nurses of the sick and mothers of infants, who will sleep through much noise of an irrelevant sort, but waken at the slightest stirring of the patient or the babe. This last fact shows the _sense-organ_ to be pervious for sounds. Many people have a remarkable faculty of registering when asleep the flight of time. They will habitually wake up at the same minute day after day, or will wake punctually at an unusual hour determined upon overnight. How can this knowledge of the hour (more accurate often than anything the waking consciousness shows) be possible without mental activity during the interval? Such are what we may call the classical reasons for admitting that the mind is active even when the person afterwards ignores the fact.[200] Of late years, or rather, one may say, of late months, they have been reinforced by a lot of curious observations made on hysterical and hypnotic subjects, which prove the existence of a highly developed consciousness in places where it has hitherto not been suspected at all. These observations throw such a novel light upon human nature that I must give them in some detail. That at least four different and in a certain sense rival observers should agree in the same conclusion justifies us in accepting the conclusion as true. _'Unconsciousness' in Hysterics._