[5] Alrutz’s views are summarized in Psychological Review, Sept., 1901.

[6] Die Spiele der Menschen, 1899, p. 206.

[7] L. Robinson, art.  “Ticklishness,” Tuke’s Dictionary of Psychological Medicine.

[8] Stanley Hall and Allin, “Tickling and Laughter,” American Journal of Psychology, October, 1897.

[9] H.M.  Stanley, “Remarks on Tickling and Laughter,” American Journal of Psychology, vol. ix, January, 1898.

[10] Simpson, “On the Attitude of the Foetus in Utero,” Obstetric Memoirs, 1856, vol. ii.

[11] Erasmus Darwin, Zooenomia, Sect.  XVII, 4.

[12] Hyades and Deniker, Mission Scientifique du Cap Horn, vol. vii. p. 296.

[13] Such an interpretation is supported by the arguments of W. McDougall ("The Theory of Laughter,” Nature, February 5, 1903), who contends, without any reference to the sexual field, that one of the objects of laughter is automatically to “disperse our attention.”

[14] Even the structure of the vaginal mucous membrane, it may be noted, is analogous to that of the skin.  D. Berry Hart, “Note on the Development of the Clitoris, Vagina, and Hymen,” Transactions of the Edinburgh Obstetrical Society, vol. xxi, 1896.

[15] W.H.B.  Stoddart, “Anaesthesia in the Insane,” Journal of Mental Science, October, 1899.

[16] Gina Lombroso, “Sur les Reflexes Cutanes,” International Congress of Criminal Anthropology, Amsterdam, Comptes Rendus, p. 295.

III.

The Secondary Sexual Skin Centres—­Orificial Contacts—­Cunnilingus and Fellatio—­The Kiss—­The Nipples—­The Sympathy of the Breasts with the Primary Sexual Centres—­This Connection Operative both through the Nerves and through the Blood—­The Influence of Lactation on the Sexual Centres—­Suckling and Sexual Emotion—­The Significance of the Association between Suckling and Sexual Emotion—­This Association as a Cause of Sexual Perversity.

We have seen that the skin generally has a high degree of sensibility, which frequently tends to be in more or less definite association with the sexual centres.  We have seen also that the central and specific sexual sensation, the sexual embrace itself, is, in large measure, a specialized kind of skin reflex.  Between the generalized skin sensations and the great primary sexual centre of sensation there are certain secondary sexual centres which, on account of their importance, may here be briefly considered.

These secondary centres have in common the fact that they always involve the entrances and the exits of the body—­the regions, that is, where skin merges into mucous membrane, and where, in the course of evolution, tactile sensibility has become highly refined.  It may, indeed, be said generally of these frontier regions of the body that their contact with the same or a similar frontier region in another person of opposite sex, under conditions otherwise favorable to tumescence, will tend to produce a minimum and even sometimes a maximum degree of sexual excitation.  Contact of these regions with each other or with the sexual region itself so closely simulates the central sexual reflex that channels are set up for the same nervous energy and secondary sexual centres are constituted.