There are several theories as to the nature of this subterranean stratum of our being--this hidden self--each of which finds its champion in the modern psychological schools. First, there is the theory that it consists merely in the mechanical workings of the brain--a purely physiological theory, which makes the subconscious mind synonymous with certain brain activities--much the same as a series of complex reactions. It is well known that there is a brain-change corresponding to every thought we think; and the nature of the connection between the two has been one of the most debated points in metaphysics, and is one which, if we thoroughly understood it, would doubtless solve in a great measure the nature of life and of consciousness. Without going into this very complex question, however, there remains the undoubted _fact_ of the connection; the thought, which is known by us in consciousness; and the brain-change, which has been verified by ingenious mechanical and electrical instruments, and the effects of which we behold in the chemical changes in the brain-substance itself after severe thinking. This being so, it has been said, Why not suppose that so-called subconscious actions _are_ merely brain activities which take place, but which have never risen into consciousness? Professor Muensterberg and others hold this view. It has been conclusively shown, however, by Dr. Morton Prince and others, that this theory fails to explain adequately many of the facts--seems indeed contrary to much experimental evidence; and this view is now given up by all but the most materialistic of the modern psychological school. We have to search deeper yet for the mystery of the subconscious mind; and we shall have to grant it a certain amount of consciousness of its own, apart from all purely brain activity. A very opposite theory is that advanced by Mr. F. W. H. Myers--that of the "subliminal self." This theory says that the conscious mind is but an infinitely small part of our total self--a mere fragment; that portion best adapted to meet the needs of everyday life. To borrow an analogy from physics, "consciousness is only the visible portion of the spectrum; the invisible, ultra portions are our subconscious selves." I shall not venture upon a criticism of this theory beyond saying that the majority of modern psychologists do not hold to it; and hence, whether it be ultimately true or false, we must disregard it for our present purposes.