Hence it is that some of the most profound thinkers who have discussed the subject of dreams, like Descartes and Leibnitz, Jouffroy and Dugald Stewart, Richard and Carus, with a number of others, assert the uninterrupted wakefulness of the mind. Some authors believe that the spiritual part of man needs no sleep, but delights in the comfort of feeling that the body is in perfect repose, and of forgetting, by these means, for a time the troubles of daily life, and the responsibilities of our earthly existence. They base this view upon the fact, that, as far as we can judge, the mind is, during sleep, independent of the body and the outer world. Thinking is quite possible during sleep without dreaming, and certain bodily sensations, even, are correctly perceived, as when we turn over in our sleep, because lying on one side produces pain or uneasiness. We not only talk while we are asleep, but laugh or weep, sigh or groan. A slight noise, a whispered word, affect the course of our thoughts, and produce new images in our dreams, as certain affections and even the pressure upon certain organs are sure to produce invariably the same dreams. Space and time disappear, however, and naturally, because we can measure them only by the aid of our senses, and these are, for the time, inactive. Hence Dugald Stewart ascribes the manner in which a moment's dream often comprises a year, or a whole lifetime, to the fact that, when we are asleep, the images created by our imagination appear to be realities, while those which we form when we are awake are known to us to be mere fictions, and hence not subject to the laws of time.