This function of dreams becomes especially well marked when there arises some incentive for the sense perception. That the senses aroused during sleep influence the dream is well known, and can be experimentally verified; it is one of the certain but much overestimated results of the medical investigation of dreams. Hitherto there has been an insoluble riddle connected with this discovery. The stimulus to the sense by which the investigator affects the sleeper is not properly recognized in the dream, but is intermingled with a number of indefinite interpretations, whose determination appears left to psychical free-will. There is, of course, no such psychical free-will. To an external sense-stimulus the sleeper can react in many ways. Either he awakens or he succeeds in sleeping on. In the latter case he can make use of the dream to dismiss the external stimulus, and this, again, in more ways than one. For instance, he can stay the stimulus by dreaming of a scene which is absolutely intolerable to him. This was the means used by one who was troubled by a painful perineal abscess. He dreamt that he was on horseback, and made use of the poultice, which was intended to alleviate his pain, as a saddle, and thus got away from the cause of the trouble. Or, as is more frequently the case, the external stimulus undergoes a new rendering, which leads him to connect it with a repressed desire seeking its realization, and robs him of its reality, and is treated as if it were a part of the psychical matter. Thus, some one dreamt that he had written a comedy which embodied a definite _motif_; it was being performed; the first act was over amid enthusiastic applause; there was great clapping. At this moment the dreamer must have succeeded in prolonging his sleep despite the disturbance, for when he woke he no longer heard the noise; he concluded rightly that some one must have been beating a carpet or bed. The dreams which come with a loud noise just before waking have all attempted to cover the stimulus to waking by some other explanation, and thus to prolong the sleep for a little while.