Stanley Hall and Allin in their investigation of the phenomena of
tickling, largely carried out among young women teachers, found
that in 60 clearly marked cases ticklishness was more marked at
one time than another, "as when they have been 'carrying on,' or
are in a happy mood, are nervous or unwell, after a good meal,
when being washed, when in perfect health, when with people they
like, etc." (Hall and Allin, "Tickling and Laughter," _American
Journal of Psychology_, October, 1897.) It will be observed that
most of the conditions mentioned are such as would be favorable
to excitations of an emotionally sexual character.

The palms of the hands may be very ticklish during sexual
excitement, especially in women, and Moll (_Konträre
Sexualempfindung_, p. 180) remarks that in some men titillation
of the skin of the back, of the feet, and even of the forehead
evokes erotic feelings.

It may be added that, as might be expected, titillation of the
skin often has the same significance in animals as in man. "In
some animals," remarks Louis Robinson (art. "Ticklishness,"
_Dictionary of Psychological Medicine_), "local titillation of
the skin, though in parts remote from the reproductive organs,
plainly acts indirectly upon them as a stimulus. Thus, Harvey
records that, by stroking the back of a favorite parrot (which he
had possessed for years and supposed to be a male), he not only
gave the bird gratification,--which was the sole intention of the
illustrious physiologist,--but also caused it to reveal its sex
by laying an egg."

The sexual significance of tickling is very clearly indicated by the fact