The world which we enter through the portal of sleep presents such obvious and serious limitations that we are apt to under-estimate its real richness and variety. In some respects, indeed, we can accomplish in sleep what is beyond our reach awake. Thus it sometimes happens that we reason better in sleep than when awake, that we may find in dreams the solutions of difficulties which escape us awake, and that we may remember things which, when awake, we had forgotten. But even within the ordinary range of experience, it is interesting to note that our dreams contain the same elements as our waking life. The sensory activities which stir us during the day are equally active, though in strange transformations, in the world of dreams. It is probable that all the senses may furnish the medium through which stimuli may reach sleeping consciousness; though touch and hearing are doubtless the main channels to dream life. The eyes are closed, so that while the chief parts of our dream life are in terms of vision, direct visual stimuli can only be a very dim and uncertain influence. But no sense is absolutely excluded from activity in dreams.[57] Heat or cold sensations and pressure sensations, as well as their anaesthetic absence, undoubtedly play an important part in explaining various kinds of dreams. They do not necessarily result in rememberable dreams, even although it is possible that they still affect the current of sleeping consciousness. It is possible to press and massage the body of a sleeper all over, gently but firmly, without interrupting sleep. When the pressure reaches a considerable degree of vigour, the sleeper may move a muscle, perhaps the lips, even an arm, may go so far as to half wake and move the whole body. All these movements suggest that they have accompaniments on the psychic side, yet, on finally awakening, the sleeper may be unable to recall any memory of the occurrence, or any vestige of a dream. In a certain proportion of cases, however, a dream results. Thus a lady dreams that, with a number of other people, she is on board a ship which is rocking heavily, and on awakening she finds that her large dog is on the bed, vigorously scratching himself. The ship has clearly been the theory invented by sleeping consciousness to account for the unfamiliar sensations of movement.