ticklishness which could not fail to be recognized. This connection is,
indeed, the basis of Spinoza's famous definition of love,--"_Amor est
titillatio quædam concomitante idea causæ externæ_,"--a statement which
seems to be reflected in Chamfort's definition of love as "_l'échange de
deux fantaisies, et le contact de deux epidermes_." The sexual act, says
Gowers, is, in fact, a skin reflex.[14] "The sexual parts," Hall and Allin
state, "have a ticklishness as unique as their function and as keen as
their importance." Herrick finds the supreme illustration of the summation
and irradiation theory of tickling in the phenomena of erotic excitement,
and points out that in harmony with this the skin of the sexual region is,
as Dogiel has shown, that portion of the body in which the tactile
corpuscles are most thoroughly and elaborately provided with anastomosing
fibres. It has been pointed out[15] that, when ordinary tactile
sensibility is partially abolished,--especially in hemianæsthesia in the
insane,--some sexual disturbance is specially apt to be found in
association.

In young children, in girls even when they are no longer children, and
occasionally in men, tickling may be a source of acute pleasure, which in
very early life is not sexual, but later tends to become so under
circumstances predisposing to the production of erotic emotion, and
especially when the nervous system is keyed up to a high tone favorable
for the production of the maximum effect of tickling.

"When young," writes a lady aged 28, "I was extremely fond of
being tickled, and I am to some extent still. Between the ages of
10 and 12 it gave me exquisite pleasure, which I now regard as
sexual in character. I used to bribe my younger sister to tickle
my feet until she was tired."