into old age, its existence in
the castrated and in the congenital absence of the sexual glands;
he pointed out that even with an apparently sound and normal
sexual apparatus all sorts of psychic pathological deviations may
yet occur. In fact, all the lines of argument I have briefly
indicated in the foregoing pages--although when they were first
written this fact was unknown to me--had been fully discussed by
this remarkable man nearly a century ago. (The greater part of
the third volume of Gall's _Sur les Fonctions du Cerveau_, in the
edition of 1825, is devoted to this subject. For a good summary,
sympathetic, though critical, of Gall's views on this matter, see
Moebius, "Ueber Gall's Specielle Organologie," _Schmidt's
Jahrbuecher der Medicin_, 1900, vol. cclxvii; also _Ausgewahlte
Werke_, vol. vii.)

It will be seen that the question of the nature of the sexual impulse has
been slowly transformed. It is no longer a question of the formation of
semen in the male, of the function of menstruation in the female. It has
become largely a question of physiological chemistry. The chief parts in
the drama of sex, alike on its psychic as on its physical sides, are thus
supposed to be played by two mysterious protagonists, the hormones, or
internal secretions, of the testes and of the ovary. Even the part played
by the brain is now often regarded as chemical, the brain being considered
to be a great chemical laboratory. There is a tendency, moreover, to
extend the sexual sphere so as to admit the influence of internal
secretions from other glands. The thymus, the adrenals, the thyroid, the
pituitary, even the kidneys: it is possible that internal secretions from
all these glands may combine to fill in the complete picture of sexuality
as we know it in men and women.[16] The subject is, however, so complex
and at present so little known that it would be hazardous, and for the
present purpose it is needless, to attempt to set forth any conclusions.

It is sufficiently clear that there is on the surface a striking analogy
between sexual desire and the impulse to evacuate an excretion, and that
this analogy is not only seen in the frog, but extends also to the highest
vertebrates. It is quite another matter, however, to assert that the
sexual impulse can be adequately defined as an impulse to evacuate. To
show fully the inadequate nature of this conception would require a
detai