[34] My references to Dr. Robinson’s views are partly to the article in the _Dictionary_ already quoted, and partly to notes of lectures given before the British Association and the West Kent Medical Society, which he has been so kind as to show me. I have made much use of his interesting and often brilliant suggestions in dealing with the subject of ticklishness. [35] Both of these are included by Dr. Richet among the most sensitive parts (_loc. cit._). [36] How far the results are complicated by the action of the muscles which serve to erect the separate hairs on the body, and are said by Lister to contract near a tickled surface, I am not sure. [37] _E.g._, Külpe, _op. cit._, 147. [38] _Expression of the Emotions_, p. 201. [39] In using the expression “ticklish period,” I do not imply that ticklishness necessarily disappears after a certain period of maximal intensity. Like play, it probably persists in a certain number of persons as a susceptibility to which the laws of propriety leave but little scope for exercise. [40] _Op. cit._, pp. 201, 202. The restriction I have added enables us to include the case of the sole of the foot. [41] _Loc. cit._ Dr. L. Hill confirms the observation and offers the same explanation. [42] In this connection an observation sent me by Dr. L. Hill is significant. His little girl first responded with laughter to tickling under the armpits at the same age (two and a half years) as she first showed fear by crying on being put into the arms of a stranger. [43] G. Heymans, _Zeitschrift für die Psychol. und die Physiol. der Sinne_, Bd. xi., ss. 31 ff. [44] Heymans, _loc. cit._ [45] The abnormal forms of automatic laughter, including the effects of stimulants, are dealt with by Raulin, _op. cit._, 2^{ème} partie, chap. iv., and 3^{ème} partie. [46] Given in the returns to Stanley Hall’s inquiries. This explosion of laughter on receiving sad news occurs in cases of cerebral disorder. See Dugas, _op. cit._, p. 16. [47] Quoted by Dugas, _op. cit._, p. 12. [48] Shakespeare makes Lady Macbeth perpetrate a pun in a moment of intense excitement when Macbeth’s hesitation goads her into a resolve to carry out the murder herself:— “I’ll gild the faces of the grooms withal For it must seem their guilt”. Did he mean to illustrate by this the way in which emotional strain tends to lapse for a brief moment into laughter? [49] _Op. cit._, pp. 163, 208. [50] See _Les Passions de l’áme_, 2^{ème} partie, art. 25. [51] Co-operative teasing, when it methodically “nags” a boy because he happens, for example, to take the unfashionable side in some political dispute, making his school-life a torment, had—with all deference to apologetic headmasters, be it said—better change its name. [52] Given by Stanley Hall in the article, “The Psychology of Tickling,” etc., already quoted.