nce.[99]

The importance of the lips as a normal erogenous zone is shown by
the experiments of Gualino. He applied a thread, folded on itself
several times, to the lips, thus stimulating them in a simple
mechanical manner. Of 20 women, between the ages of 18 and 35,
only 8 felt this as a merely mechanical operation, 4 felt a
vaguely erotic element in the proceeding, 3 experienced a desire
for coitus and in 5 there was actual sexual excitement with
emission of mucus. Of 25 men, between the ages of 20 and 30, in
15 all sexual feeling was absent, in 7 erotic ideas were
suggested with congestion of the sexual organs without erection,
and in 3 there was the beginning of erection. It should be added
that both the women and the men in whom this sexual reflex was
more especially marked were of somewhat nervous temperament; in
such persons erotic reactions of all kinds generally occur most
easily. (Gualino, "Il Rifflesso Sessuale nell' eccitamento alle
labbre," _Archivio di Psichiatria_, 1904, p. 341.)

As tumescence, under the influence of sensory stimulation, proceeds toward
the climax when it gives place to detumescence, the physical phenomena
become more and more acutely localized in the sexual organs. The process
which was at first predominantly nervous and psychic now becomes more
prominently vascular. The ancient sexual relationship of the skin asserts
itself; there is marked surface congestion showing itself in various ways.
The face tends to become red, and exactly the same phenomenon is taking
place in the genital organs; "an erection," it has been said, "is a
blushing of the penis." The difference is that in the genital organs this
heightened vascularity has a definite and specific function to
accomplish--the erection of the male organ which fits it to enter the
female parts--and that consequently there has been developed in the penis
that special kind of vascular mechanism, consisting of veins in connective
tissue with unstriped muscular fibers, termed erectile tissue.[100]

It is not only the man who is supplied with erectile tissue which in the
process of tumescence becomes congested and swollen. The woman also, in
the corresponding external genital region, is likewise supplied with
erectile tissue now also charged with blood, and exhibits the same changes
as have taken place in her partner, though less conspicuously visible. In
the anthropoid apes,