Our unconscious mind contains many millions of past experiences that, so far as our conscious mind knows, are lost forever. By means of several devices, we now know how to bring back lost memories. One method is "free association", used by psychiatrists. If a patient lets his conscious mind wander at will, it can give him clues to forgotten things which, if skilfully pursued by the doctor, will bring up whole networks of lost ideas and forgotten terrors. There are certain drugs which also help in this process: hypnotism, too, can be of tremendous value in exploring a patient's unconscious.