[50] Ueber die phantastischen Gesichsterscheinungen, p. 45.
[51] Another side of histrionic illusion, the reading of the imitated feelings into the actors' minds, will be dealt with in a later chapter.
[52] In a finished painting of any size this preparation is hardly necessary. In these cases, in spite of the great deviations from truth in pictorial representation already touched on, the amount of essential agreement is so large and so powerful in its effect that even an intelligent animal will experience an illusion. Mr. Romanes sends me an interesting account of a dog, that had never been accustomed to pictures, having been put into a state of great excitement by the introduction of a portrait into a room, on a level with his eye. It is not at all improbable that the lower animals, even when sane, are frequently the subjects of slight illusion. That animals dream is a fact which is observed as long ago as the age of Lucretius.
[53] This kind of illusion is probably facilitated by the fact that the eye is often performing slight movements without any clear consciousness of them. See what was said about the limits of sensibility, p. 50.
[54] Mental Physiology, fourth edit., p. 158.
[55] In persons of very lively imagination the mere representation of an object or event may suffice to bring about such a semblance of sensation. Thus, M. Taine (op. cit., vol. i. p. 94) vouches for the assertion that "one of the most exact and lucid of modern novelists," when working out in his imagination the poisoning of one of his fictitious characters, had so vivid a gustatory sensation of arsenic that he was attacked by a violent fit of indigestion.
[56] Mentioned by Dr. Carpenter (Mental Physiology, p. 207), where other curious examples are to be found.
[57] See Annales Médico-Psychologiques, tom. vi. p. 168, etc.; tom. vii. p. 1, etc.
[58] I have already touched on the resonance of a sense-impression when the stimulus has ceased to act (see p. 55). The remarks in the text hold good of all such after-impressions, in so far as they take the form of fully developed percepts. A good example is the recurrence of the images of microscopic preparations, to which the anatomist is liable. (See Lewes, Problems of Life and Mind, third series, vol. ii. p. 299.) Since a complete hallucination is supposed to involve the peripheral regions of the nerve, the mere fact of shutting the eye would not, it is clear, serve as a test of the origin of the illusion.
[59] That subjective sensation may become the starting-point in complete hallucination is shown in a curious instance given by Lazarus, and quoted by Taine, op. cit., vol. i. p. 122, et seq. The German psychologist relates that, on one occasion in Switzerland, after gazing for some time on a chain of snow-peaks, he saw an apparition of an absent friend, looking like a corpse. He goes on to explain that this phantom was the product of an image of recollection which somehow managed to combine itself with the (positive) after-image left by the impression of the snow-surface.