to suspend the sleep at the proper time. It acts like a conscientious night-watchman, who first does his duty by quelling disturbances so as not to waken the citizen, but equally does his duty quite properly when he awakens the street should the causes of the trouble seem to him serious and himself unable to cope with them alone.

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