following
general laws as suggested or established. It seems to be provided in the
most generous manner that the process of sexual excitement--the nature
of which certainly remains quite mysterious to us--should be set in
motion. The factor making this provision in a more or less direct way is
the excitation of the sensible surfaces of the skin and sensory organs,
while the most immediate exciting influences are exerted on certain
parts which are designated as erogenous zones. The criterion in all
these sources of sexual excitement is really the quality of the stimuli,
though the factor of intensity (in pain) is not entirely unimportant.
But in addition to this there are arrangements in the organism which
induce sexual excitement as a subsidiary action in a large number of
inner processes as soon as the intensity of these processes has risen
above certain quantitative limits. What we have designated as the
partial impulses of sexuality are either directly derived from these
inner sources of sexual excitation or composed of contributions from
such sources and from erogenous zones. It is possible that nothing of
any considerable significance occurs in the organism that does not
contribute its components to the excitement of the sexual impulse.

It seems to me at present impossible to shed more light and certainty on
these general propositions, and for this I hold two factors responsible;
first, the novelty of this manner of investigation, and secondly, the
fact that the nature of the sexual excitement is entirely unfamiliar to
us. Nevertheless, I will not forbear speaking about two points which
promise to open wide prospects in the future.

*Diverse Sexual Constitutions.*--(_a_) We have considered above the
possibility of establishing the manifold character of congenital sexual
constitutions through the diverse formation of the erogenous zones; we
may now attempt to do the same in dealing with the indirect sources of
sexual excitement. We may assume that, although these different sources
furnish contributions in all individuals, they are not all equally
strong in all persons; and that a further contribution to the
differentiation of the diverse sexual constitution will be found in the
preferred developments of the individual sources of sexual excitement.

*The Paths of Opposite Influences.*--(_b_) Since we are now dropping the
figurative manner of expression hitherto employed, by which we spoke of
_sources_ of sexual e