memory of an
attractive woman may be just as effective in causing erection as if she
were actually visible at the moment; reading erotic literature may have
the same result. When the sexual impulse is perverted, the ideas causing
erection will naturally be themselves of a perverse character. Thus, in
the homosexual male, erection occurs at the sight or remembrance of a
man; in the fetichist, the idea of the fetich is operative--in the case
of the body-linen fetichist, for instance, the idea of articles of
underclothing.

In the second place, the activity of the erection centre can be aroused
by physical stimuli. To this category belong masturbatory manipulations,
stimulation of the glans penis and other parts of the genital organs.
But other erogenic areas exist, the stimulation of which produces the
same results. Among these areas, the buttocks must be particularly
mentioned. But individual peculiarities play a great part in this
connexion. Thus, in many persons, a slight stimulation of the nape of
the neck, of the scalp, &c., has an erogenic effect. In all cases alike,
the stimulus is conducted along the sensory nerves to the erection
centre, and it is the stimulation of this centre which by reflex action
leads to distension of the penis with blood and its consequent erection.
The physical stimulus leading to erection may also result from some
pathological process, such as inflammation of the penis or of the
urethra. Finally, certain internal physiological processes may be the
starting-point of the afferent physical stimuli leading to erection; for
example, distension of the bladder, and also of the seminal vesicles,
and of the seminiferous tubules of the testicle. In addition, it is
probable that many of the processes of growth occurring in the
reproductive glands act in a similar way. These internal stimuli all
pass to the erection centre along the afferent (sensory) nerves, and
induce erection by reflex action; and it is important to bear in mind
that this effect may result without any direct affection of
consciousness by the originating afferent impulses.

Although either kind of stimuli, psychical or physical, acting alone,
may give rise to erection, experience shows that in most instances the
two varieties co-operate in the production of this effect. Thus, in the
sexually mature man, the accumulation of semen in the seminal vesicles
gives rise, not only to excitement of the erection centre, but also to
voluptu