[103] Helmholtz, P. O. 438. The question will soon come before us again in the chapter on the Perception of Space.
[104] C. F. Taylor, Sensation and Pain, p. 37 (N. Y., 1882).
[105] Examen Critique de la Loi Psychophysique (1883), p. 61.
[106] Compare A. W Volkmann's essay 'Ueber Ursprüngliches und Erworbenes in den Raumanschauungen,' on p. 139 of his Untersuchungen im Gebiete der Optik; and Chapter xiii of Hering's contribution to Hermann's Handbuch der Physiologie, vol. iii.
[107] In the Proceedings of the American Society for Psychical Research, pp. 253-4, I have tried to account for some of the variations in this consciousness. Out of 140 persons whom I found to feel their lost foot, some did so dubiously. "Either they only feel it occasionally, or only when it pains them, or only when they try to move it; or they only feel it when they 'think a good deal about it' and make an effort to conjure it up. When they 'grow inattentive,' the feeling 'flies back' or 'jumps back,' to the stump. Every degree of consciousness, from complete and permanent hallucination down to something hardly distinguishable from ordinary fancy, seems represented in the sense of the missing extremity which these patients say they have. Indeed I have seldom seen a more plausible lot of evidence for the view that imagination and sensation are but differences of vividness in an identical process than these confessions, taking them altogether, contain. Many patients say they can hardly tell whether they feel or fancy the limb."
[108] Pflüger's Archiv, xxxvii. 1.
[109] Not all patients have this additional illusion.
[110] I ought to say that in almost all cases the volition is followed by actual contraction of muscles in the stump.
[111] Cf. Herbart, Psychol. als. Wissenschaft, § 125.
[112] Compare the historical reviews by K. Lange: Ueber Apperception (Plauen, 1879), pp. 12-14; by Staude in Wundt's Philosophische Studien, i. 149; and by Marty in Vierteljsch. f. wiss. Phil., x. 347 ff.