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 detailed consideration of the facts of sexual life. That is, however, unnecessary. It is enough to point out certain considerations which alone suffice to invalidate this view. In the first place, it must be remarked that the trifling amount of fluid emitted in sexual intercourse is altogether out of proportion to the emotions aroused by the act and to its after-effect on the organism; the ancient dictum _omne animal post coitum triste_ may not be exact, but it is certain that the effect of coitus on the organism is far more profound than that produced by the far more extensive evacuation of the bladder or bowels. Again, this definition leaves unexplained all those elaborate preliminaries which, both in man and the lower animals, precede the sexual act, preliminaries which in civilized human beings sometimes themselves constitute a partial satisfaction to the sexual impulse. It must also be observed that, unlike the ordinary excretions, this discharge of the sexual glands is not always, or in every person, necessary at all. Moreover, the theory of evacuation at once becomes hopelessly inadequate when we apply it to women; no one will venture to claim that an adequate psychological explanation of the sexual impulse in a woman is to be found in the desire to expel a little bland mucus from the minute glands of the genital tract.