The sense of touch is so universally diffused over the whole skin, and in
so many various degrees and modifications, and it is, moreover, so truly
the Alpha and the Omega of affection, that a broken and fragmentary
treatment of the subject has been inevitable.

The skin is the archæological field of human and prehuman experience, the
foundation on which all forms of sensory perception have grown up, and as
sexual sensibility is among the most ancient of all forms of sensibility,
the sexual instinct is necessarily, in the main, a comparatively slightly
modified form of general touch sensibility. This primitive character of
the great region of tactile sensation, its vagueness and diffusion, the
comparatively unintellectual as well as unæsthetic nature of the mental
conceptions which arise on the tactile basis make it difficult to deal
precisely with the psychology of touch. The very same qualities, however,
serve greatly to heighten the emotional intensity of skin sensations. So
that, of all the great sensory fields, the field of touch is at once the
least intellectual and the most massively emotional. These qualities, as
well as its intimate and primitive association with the apparatus of
tumescence and detumescence, make touch the readiest and most powerful
channel by which the sexual sphere may be reached.

In disentangling the phenomena of tactile sensibility ticklishness has
been selected for special consideration as a kind of sensation, founded on
reflexes developing even before birth, which is very closely related to
sexual phenomena. It is, as it were, a play of tumescence, on which
laughter supervenes as a play of detumescence. It leads on to the more
serious phenomena of tumescence, and it tends to die out after
adolescence, at the period during which sexual relationships normally