This subconscious region of the mind is the great record-file of everything we have ever experienced, thought or known. Everything is recorded there. The best authorities now generally agree that there is no such thing as an absolute forgetting of even the most minute impression, notwithstanding the fact that we may be unable to recollect or remember it, owing to its faintness, or lack of associated "indexing." It is held that everything is to be found in that subconscious index-file, if we can only manage to find its place. Kay says: "In like manner we believe that every impression or thought that has once been before consciousness remains ever afterward impressed upon the mind. It may never again come up before consciousness, but it will doubtless remain in that vast ultra-conscious region of the mind, unconsciously moulding and fashioning our subsequent thoughts and actions. It is only a small part of what exists in the mind that we are conscious of. There is always much that is known to be in the mind that exists in it unconsciously, and must be stored away somewhere. We may be able to recall it into consciousness when we wish to do so; but at other times the mind is unconscious of its existence. Further, every one's experience must tell him that there is much in his mind that he cannot always recall when he may wish to do so,--much that he can recover only after a labored search, or that he may search for in vain at the time, but which may occur to him afterwards when perhaps he is not thinking about it. Again, much that we probably would never be able to recall, or that would not recur to us under ordinary circumstances, we may remember to have had in the mind when it is mentioned to us by others. In such a case there must still have remained some trace or scintilla of it in the mind before we could recognize it as having been there before."
Morell says: "We have every reason to believe that mental power when once called forth follows the analogy of everything we see in the material universe in the fact of its perpetuity. Every single effort of mind is a creation which can never go back again into nonentity. It may slumber in the depths of forgetfulness as light and heat slumber in the coal seams, but there it is, ready at the bidding of some appropriate stimulus to come again out of the darkness into the light of consciousness." Beattie says: "That which has been long forgotten, nay, that which we have often in vain endeavored to recollect, will sometimes without an effort of ours occur to us on a sudden, and, if I may so speak, of its own accord." Hamilton says: "The mind frequently contains whole systems of knowledge which, though in our normal state they may have faded into absolute oblivion, may in certain abnormal states, as madness, delirium, somnambulism, catalepsy, etc., flash out into luminous consciousness.... For example, there are cases in which the extinct memory of whole languages were suddenly restored." Lecky says: "It is now fully established that a multitude of events which are so completely forgotten that no effort of the will can revive them, and that the statement of them calls up no reminiscences, may nevertheless be, so to speak, embedded in the memory, and may be reproduced with intense vividness under certain physical conditions."