The subject of the significance of dreams, so long ignored, has suddenly become a matter of energetic study and of fiery controversy the world over. The cause of this revival of interest is the new point of view brought forward by Professor Bergson in the paper which is here made accessible to the English-reading public. This is the idea that we can explore the unconscious substratum of our mentality, the storehouse of our memories, by means of dreams, for these memories are by no means inert, but have, as it were, a life and purpose of their own, and strive to rise into consciousness whenever they get a chance, even into the semi-consciousness of a dream. To use Professor Bergson's striking metaphor, our memories are packed away under pressure like steam in a boiler and the dream is their escape valve.