The special process which secures this union of the male and female elements is termed copulation or coitus. It takes place in all warm-blooded animals, as well as many others, but in man, with his highly developed mental and psychical qualities, it is a truly complex experience in which body, mind and soul all take their part.
Physically its central fact is the ejaculation of the seminal fluid by the male and its reception by the female, and this culmination with its psychical concomitants is spoken of as the orgasm. Before coitus is feasible, the organs designed for the purpose have to be brought into an appropriate state for its consummation. The penis and the vulva are alike furnished with erectile tissue. The penis has to be erected in order to penetrate into the vagina, while the female organs add their share in facilitating the act both by the erection of the tissue round the vulva and by the outpouring of a lubricating secretion which bathes all the parts. The mechanism of this is a nervous one, and its originating cause while partly physical is chiefly mental, due to the emotions aroused by love and courtship, and thus in every act of coitus properly realized, an essential preliminary is an abbreviated courtship. This initial stage has been described as the stage of tumescence, and is succeeded by the introduction of the male organ into the vagina. A motor nerve discharge follows which produces ejaculation of the seminal fluid and is for the male the climax of the orgasm. The female is, however, by no means passive; motor nerve discharges take place leading to rhythmic contraction of the vagina, and she experiences, or should experience, a similar orgasm to the male. The climax is followed in both by a feeling of satisfaction and repose which generally issues in refreshing sleep. It is to be noted, however, that in the female the whole process is apt to be slower than in the male. Her orgasm frequently coincides with the male, but often it comes later. If this is not realized by her partner, and inconsiderate haste be practiced, then, in place of satisfaction, a state of nervous tension may remain, which is not only psychically deleterious, but, if repeated, may lead to actual illness.
I have spoken of the sex act as it should be, a fine and lofty emotional experience of two people between whom is the bond of love. It is true that in the female an entirely passive part is physiologically possible, and it is also true that in the male, who is biologically the hunting and pursuing animal, spontaneous desires arise from time to time which are too often accorded a bodily and disharmonious satisfaction. Disharmonious because it cannot be too strongly insisted upon that the completely satisfactory realization of the sex act involves the participation of every side of human nature, spiritual and physical, and is the outcome of an intense desire for perfect unity with the beloved. Hence mere bodily satisfaction of sensuous desire must have a disharmonious and deteriorating effect, because it ignores a basal fact of man, namely spirit, and leaves that side of him starved and unsatisfied. And the same is true of all sexual aberrations and perversions. Though they may seem at the moment to be unimportant, the fact remains that they are sins against both the spirit and the flesh, and are followed inexorably by their own punishment.
It is argued by some that the sexual act should be restricted to occasions, when there is a definite intention of begetting children. This does not seem either reasonable or desirable. Nature's plans were certainly, in the case of human beings, not constructed on that basis. It would introduce an element of calculation and deliberation into what is naturally a finely spontaneous thing, and it would put a quite unnecessary, and in some cases, at least, a harmful, strain upon two people. As Havelock Ellis has put it: "Even if sexual relationships had no connection with procreation whatever, they would still be justifiable, and are, indeed, an indispensable aid to the best moral development of the individual; for it is only in so intimate a relationship as that of sex that the finest graces and aptitudes of life have full scope." This does not imply that married life does not call for the exercise of self-restraint and continence, in this as in other respects.
Those who regard marital relations as an opportunity for unbridled sexual indulgence are not likely to win success in an adventure of considerable difficulty in which all that is fine in man or woman will find full scope for development. But it does mean that sexual intimacy has a value in itself as an expression in the terms of the body of the love which unites husband and wife, and that, when duly controlled, it leads to health and general harmony.