under conditions otherwise favorable to tumescence, will tend to produce a
minimum and even sometimes a maximum degree of sexual excitation. Contact
of these regions with each other or with the sexual region itself so
closely simulates the central sexual reflex that channels are set up for
the same nervous energy and secondary sexual centres are constituted.

It is important to remember that the phenomena we are here concerned with
are essentially normal. Many of them are commonly spoken of as
perversions. In so far, however, as they are aids to tumescence they must
be regarded as coming within the range of normal variation. They may be
considered unæsthetic, but that is another matter. It has, moreover, to be
remembered that æsthetic values are changed under the influence of sexual
emotion; from the lover's point of view many things are beautiful which
are unbeautiful from the point of view of him who is not a lover, and the
greater the degree to which the lover is swayed by his passion the greater
the extent to which his normal æsthetic standard is liable to be modified.
A broad consideration of the phenomena among civilized and uncivilized
peoples amply suffices to show the fallacy of the tendency, so common
among unscientific writers on these subjects, to introduce normal æsthetic
standards into the sexual sphere. From the normal standpoint of ordinary
daily life, indeed, the whole process of sex is unæsthetic, except the
earlier stages of tumescence.[17]

So long as they constitute a part of the phase of tumescence, the
utilization of the sexual excitations obtainable through these channels
must be considered within the normal range of variation, as we may
observe, indeed, among many animals. When, however, such contacts of the
orifices of the body, other than those of the male and female sexual
organs proper, are used to procure not merely tumescence, but
detumescence, they become, in the strict and technical sense, perversions.