The various forms of madness throw a clearer light on this necessary and primitive fact of human and animal perception. The act of sensation may then be said to be under its own direction, and generates itself in the automatic exercise of the brain, as in dreams, without the explicit, disturbing, and modifying influence of reflection, and the habit of rational analysis. The act of sensation is spontaneously completed and developed in and with its own constituents, and since it is isolated from other modes and exercises of thought, its real nature appears. The hallucinations of madness, produced by the mental realization of images, either detached or in association, prove that all our mental images or ideas have a tendency in themselves to become real objects of consciousness; with this difference, that a sane man recognizes these mental entifications by their mobility and incessant alterations, which contrast with the fixity and permanence of external and cosmic phenomena. The following considerations will confirm the truth of these facts. In our advanced state of civilization, thought may, after so many ages' exercise, almost be said to have become part of the organism by the indisputable effect of heredity; and the phenomenon of the recurrence to memory of past facts and distant places is obvious and intelligible, since our judgment of them is never subject to illusion, or only in rare instances and in abnormal conditions. But this judgment is less obvious and easy in the case of primitive savages who have advanced little beyond the innate exercise of the intelligence. The rational analysis of the states of consciousness has not been made, and hence their special and general distinctions are seen with difficulty or not seen at all. Consequently the primitive and natural amazement of man must have been great, when by day, and still more in the lonely silence of night, persons, places, and his own past acts recurred to his mind, and he was able to contemplate them as if they were actually present. He was incapable of giving an explanation of this marvellous fact in the rational and reflective manner which is possible to psychologists and to all civilized men. This revival of the past appeared to him as a fact in its simple and spontaneous reality; he made no attempt to explain it, but it was presented to his consciousness like all other natural facts. The only explanation of the phenomenon appeared to him to be that these images did not recur to the mind by the necessary action of the brain, but that by their own spontaneous power they were recalled to take their part within his breast: he supposed the phenomenon to be objective, not subjective.