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 hemianaesthesia 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.”

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 (Kontraere 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