Now let us question the psycho-physicists who have treated this subject according to their own special method, while coming to different conclusions. It is difficult to adopt a procedure more theoretical than theirs, or one better adapted to show the insufficiency of the intellectualist method in this domain of psychology. In truth, the subject treated by them is a special aspect of the problem, not its totality; they are inquiring whether, in the “transformation” of pleasure into pain, and _vice versâ_, there is, in the passage from one contrary to the other, a point of neutrality or indifference. Wundt graphically represents the phenomenon by a curve: the portion of this curve above the line of the abscissa has a positive value, and corresponds to the development of pleasure; the portion below corresponds to the development of pain, and has a negative value; the precise point where the curve cuts the line of the abscissa (to rise in the direction of pleasure or descend in that of pain) corresponds to neutrality or indifference. Lehmann, who, however, admits that weak sensations are neutral states, gives a curve rather different from that of Wundt. From an observation first made by Horwicz, and experiments conducted by Lehmann himself, it appears that, if one dips one’s finger into water whose temperature gradually rises from 35° to 50° Centigrade during a space of 2 minutes and 20 seconds, one feels first an agreeable warmth, then some slight, unpleasant prickings, then oscillations of intense prickings with moments of rest, and lastly, pain. His conclusion is contrary to Wundt’s, for he finds that the passage from pleasure to pain does not take place in a neutral state.[56] Footnote 56: Wundt, _Grundzüge der physiol. Psychologie_ (4th German ed.), vol. i. pp. 557 _et seq._; Lehmann, _Hauptgesetze_, etc., §§ 236-241. One of Wundt’s most distinguished pupils, Külpe, in his _Umriss der Psychologie_ (1895), considers the existence of a state of indifference “can hardly be doubted in the face of a long series of observations which support it.” (English edition, p. 242.)