Psycho-analytic speculation starts from the impression gained on investigating unconscious processes that consciousness cannot be the most general characteristic of psychic processes, but merely a special function of them. Metapsychologically expressed, it asserts that consciousness is the functioning of a particular system which may be called Bw. Since consciousness essentially yields perceptions of excitations coming from without and feelings (_Empfindungen_) of pleasure and ‘pain’ which can only be derived from within the psychic apparatus, we may allot the system W-Bw.[10] (= perceptual consciousness) a position in space. It must lie on the boundary between outer and inner, must face towards the outer world, and must envelop the other psychic systems. We then note that in this assumption we have ventured nothing new, but are in agreement with the localising tendencies of cerebral anatomy, which places the ‘seat’ of consciousness in the cortical layer, the outermost enveloping layer of the central organ. Cerebral anatomy does not need to wonder why—anatomically speaking—consciousness should be accomodated on the surface of the brain, instead of being safely lodged somewhere in the deepest recesses of it. Perhaps we may carry matters a little further than this in our deduction of such a position for our system W-Bw. Consciousness is not the only peculiar feature that we ascribe to the processes in this system. Our impressions gained by psycho-analytic experience lead us to the supposition that all excitation processes in the other systems leave in them permanent traces forming the foundations of memory-records which have nothing to do with the question of becoming conscious. They are often strongest and most enduring when the process that left them behind never reached consciousness at all. But we find it difficult to believe that such lasting traces of excitation are formed also in the system W-Bw. itself. If they remained permanently in consciousness they would very soon limit the fitness of the system for registration of new excitations;[11] on the other hand, if they became unconscious we should be confronted with the task of explaining the existence of unconscious processes in a system whose functioning is otherwise accompanied by the phenomenon of consciousness. We should, so to speak, have gained nothing and altered nothing by our supposition which relegates to a special system the process of becoming conscious. Though this may not be an absolutely binding consideration, it may at any rate lead us to conjecture that becoming conscious and leaving behind a memory-trace are processes incompatible with each other in the same system. We should thus be able to say: in the system Bw. the process of excitation becomes conscious but it leaves behind no lasting trace; all the traces of it on which memory relies would come about in the next systems inwards from the propagation of the excitation on to them.