One experiment brings out this fact clearly. On a white sheet of paper is placed a card equally white; with a fine point, but without touching the paper, the contour of the card is followed while the idea of a line traced in black is suggested to the subject. The subject, when awakened, is asked to fold the paper according to these imaginary lines. He holds the paper at the distance at which it was at the moment of suggestion, and folds it in the form of a rectangle exactly superposable on the card. A curious experiment in the same line has been often repeated by Prof. Charcot. The subject is given the suggestion of a portrait on a white card, which is then shuffled up with a dozen cards all alike. On awakening, the subject is asked to run over the collection, without being told the reason why it is wished. When he comes to the card on which had been located the imaginary portrait, he at once perceives it. One detail of these experiments is very significant. Supposing we show the imaginary portrait at a distance of two yards from the subject's eyes, the card appears white, whereas a real photograph would appear gray. If it is gradually brought nearer, the imaginary portrait at last appears, but it is necessary for it to be much nearer than an ordinary photograph for the patient to recognize the subject. By means of opera glasses we can make the patient recognize her hallucination at a distance at which she could not perceive it with the naked eye. In short, the imaginary object which figures in the hallucination is perceived under the same conditions as if it were real. Various other experiments are detailed in support of this formula. The opera glasses only act as if they were focussed upon the point of hallucination, and in the case of a short-sighted subject they had to be altered to allow for the defect of vision. If the patient looks through a prism the image is seen duplicated, although the subject is absolutely ignorant of the properties of a prism, as well as of the fact that the glass is a prism. A photograph of the plain white card used when the photograph was suggested may be substituted, and on being shown to the patient, the hallucinatory image is seen just the same, even two years after the original experiment, as was done in one case.