person who believes that he tastes poison in his food when he imagines that some one wishes to poison him, or sees an enemy lurking about his premises when he believes himself to be the victim of persecution.
Here, then, we are brought to one efficient cause of hallucinations—namely, a vividly-conceived idea which is so intense that it appears to be an actual perception, a mental image so vivid that it becomes a visual image. Everybody knows that the idea or imagination of a sensation will sometimes cause a person to feel the sensation; the mention or the sight of certain little insects which inhabit the bodies of uncleanly persons seldom fails to make the skin itch uncomfortably. John Hunter said of himself, "I am confident that I can fix my attention to any part until I have a sensation in that part." Sir Isaac Newton could call up a spectrum of the sun when he was in the dark, by intense direction of his mind to the idea of it, "as when a man looks earnestly to see a thing which is difficult to be seen." Dickens used to allege that he sometimes heard the characters of his novels actually speak to him; and a great French novelist declared that, when he wrote the description of the poisoning of one of his characters, he had the taste of arsenic so distinctly in his mouth that he was himself poisoned, had a severe attack of indigestion, and vomited all his dinner—a most pregnant proof of the power of imagination over sense, because arsenic has scarcely an appreciable taste beyond being sweetish! Artists sometimes have, in an intense form, the faculty of such vivid mental representation as to become mental presentation. It was very notable in that extraordinary genius, William Blake, poet and painter, who used constantly to see his conceptions as actual images or visions. "You have only," he said, "to work up imagination to the state of vision, and the thing is done." The power is, without doubt, consistent with perfect sanity of mind, although it may be doubtful whether a person who thought it right for himself and his wife to imitate the naked innocence of paradise in the back-garden of a Lambeth house, as Blake did, was quite sane; but too frequent exercise of the power is full of peril to the mind's stability. A person may call up images in this way, and they will come, but he may not be able to dismiss them, and they may haunt him when he would gladly be rid of them. He is like the sorcerer who has called spirits from the vasty deep, and has forgotten the spell by which to lay them again. Dr. Wigan tells of a skillful painter whom he knew, who assured him that he had once painted three hundred portraits in one year. The secret of his rapidity and success was, that he required but one sitting and painted with wonderful facility. "When a sitter came," he said, "I looked at him attentively for half an hour, sketching from time to time on the canvas. I wanted no more; I put away my canvas and took another sitter. When I wished to resume my first portrait, I took the man and set him in the chair, where I saw him as distinctly as if he had
