ar contractions, as measured by the dynamometer, than to watch the
same disk when motionless. Even in the absence of color a similar
influence of movement was noted, and watching a modified metronome
produced a greater increase of work with the ergograph than when working
to the rhythm of the metronome without watching it.[45] This psychological
fact has been independently discovered by advertisers, who seek to impress
the value of their wares on the public by the device of announcing them by
moving colored lights. The pleasure given by the ballet largely depends on
the same fact. Not only is dancing an excitation, but the spectacle of
dancing is itself exciting, and even among savages dances have a public
which becomes almost as passionately excited as the dancers
themselves.[46] It is in virtue of this effect of dancing and similar
movements that we so frequently find, both among the lower animals and
savage man, that to obtain tumescence in both sexes, it is sufficient for
one sex alone, usually the male, to take the active part. This point
attracted the attention of Kulischer many years ago, and he showed how the
dances of the men, among savages, excite the women, who watch them
intently though unobtrusively, and are thus influenced in choosing their
lovers. He was probably the first to insist that in man sexual selection
has taken place mainly through the agency of dances, games, and
festivals.[47]

It is now clear, therefore, why the evacuation theory of the sexual
impulse must necessarily be partial and inadequate. It leaves out of
account the whole of the phenomena connected with tumescence, and those
phenomena constitute the most prolonged, the most important, the most
significant stage of the sexual process. It is during tumescence that the
whole psychology of the sexual impulse is built up; it is as an incident
arising during tumescence and influencing its course that we must probably
regard nearly every sexual aberration. It is with the second stage of the
sexual process, when the instinct of detumescence arises, that the analogy
of evacuation can alone be called in. Even here, that analogy, though
real, is not complete, the nervous element involved in detumescence being
out of all proportion to the extent of the evacuation. The typical act of
evacuation, however, is a nervous process, and when we bear this in mind
we may see whatever truth the evacuation theory possesses. Beaunis classes
the sexual impulse w