ughter as a Kind of Detumescence--The Sexual
Relationships of Itching--The Pleasure of Tickling--Its Decrease with Age
and Sexual Activity.

Touch, as has already been remarked, is the least intellectual of the
senses. There is, however, one form of touch sensation--that is to say,
ticklishness--which is of so special and peculiar a nature that it has
sometimes been put aside in a class apart from all other touch sensations.
Scaliger proposed to class titillation as a sixth, or separate, sense.
Alrutz, of Upsala, regards tickling as a milder degree of itching, and
considers that the two together constitute a sensation of distinct quality
with distinct end-organs, for the mediation of that quality.[5] However we
may regard this extreme view, tickling is certainly a specialized
modification of touch and it is at the same time the most intellectual
mode of touch sensation and that with the closest connection with the
sexual sphere. To regard tickling as an intellectual manifestation may
cause surprise, more especially when it is remembered that ticklishness is
a form of sensation which reaches full development very early in life, and
it has to be admitted that, as compared even with the messages that may be
sent through smell and taste, the intellectual element in ticklishness
remains small. But its presence here has been independently recognized by
various investigators. Groos points out the psychic factor in tickling as
evidenced by the impossibility of self-tickling.[6] Louis Robinson
considers that ticklishness "appears to be one of the simplest
developments of mechanical and automatic nervous processes in the
direction of the complex functioning of the higher centres which comes
within the scope of psychology,"[7] Stanley Hall and Allin remark that
"these minimal touch excitations represent the very oldest stratum of
psychic life in the soul."[8] Hirman Stanley, in a somewhat similar
manner, pushes the intellectual element in ticklishness very far back and
associates it with "tentacular experience." "By temporary self-extension,"
he remarks, "even low amoeboid organisms have slight, but suggestive,
touch experiences that stimulate very general and violent reactions, and
in higher organisms extended touch-organs, as tentacles, antennae, hair,
etc., become permanent and very delicately sensitive organs, where minimal
contacts have very distinct and powerful reactions." Thus ticklishness
would be the survival of long pa