[132] M. Binet's highly important experiments, which were first published in vol. XVII of the Revue Philosophique (1884), are also given in full in chapter ix of his and Féré's work on 'Animal Magnetism' in the International Scientific Series. Where there is no dot on the paper, nor any other visible mark, the subject's judgment about the 'portrait' would seem to be guided by what he sees happening to the entire sheet. [133] It is a difficult thing to distinguish in a hypnotic patient between a genuine sensorial hallucination of something suggested and a conception of it merely, coupled with belief that it is there. I have been surprised at the vagueness with which such subjects will often trace upon blank paper the outlines of the pictures which they say they 'see' thereupon. On the other hand, you will hear them say that they find no difference between a real flower which you show them and an imaginary flower which you tell them is beside it. When told that one is imaginary and that they must pick out the real one, they sometimes say the choice is impossible, and sometimes they point to the imaginary flower. [134] Only the other day, to three hypnotized girls, I failed to double a hallucination with a prism. Of course it may not have been a fully-developed hallucination. [135] Brain, xi. 441. [136] Mind, x. 161, 316; and Phantasms of the Living (1886), i. 470-488. [137] In Mr. Gurney's work, just cited, a very large number of veridical cases are critically discussed. [138] Mental Evolution in Animals, p. 186. [139] _Literature._ The best treatment of perception with which I am acquainted is that in Mr. James Sully's book on 'Illusions' in the International Scientific Series. On hallucinations the literature is large. Gurney, Kandinsky (as already cited), and some articles by Kraepelin in the Vierteljahrschrift für Wissenschaftliche Philosophie, vol. v (1881), are the most systematic studies recently made. All works on Insanity treat of them. Dr. W. W. Ireland's works, 'The Blot upon the Brain' (1886) and 'Through the Ivory Gate' (1890) have much information on the subject. Gurney gives pretty complete references to older literature. The most important thing on the subject from the point of view of theory is the article by Mr. Myers on the Demon of Socrates in the Proceedings of the Society for Psychical Research for 1889, p. 522. CHAPTER XX. THE PERCEPTION OF SPACE.[140] THE FEELING OF CRUDE EXTENSITY.