THE TRANSMISSION OF THE SEMEN.--COHABITATION.
The erection is an occurrence dependent upon the centre of sexual activity. This centre, according to the investigations of Goltz, is to be sought in the lumbar portion of the spinal cord. It may be aroused to activity in manifold ways, but, above all, by means of irritations which proceed from the genitals themselves. This centre is already irritatA3d by the production of semen and the consequent filling of the testicles with spermatozoa, and they are predisposed to the liberation by other ir ritations. Not only erection, but even spontaneous emission of semen, the so-called pollution, may occur in this way as the result of powerful excitement. This centre may also be influenced by pure mental activity (erotic ideas). The different organs of sense are also in a condition to take up in many ways irritations, and to transmit them to this centre. But the brain exerts a repressive influence. If the spinal cord in animals is divided above the lumbar portion, irritations of the genitals are re sponded tO much more promptly and energetically by erections, as is also positively proven by clinical experiences in diseases of the brain, and in psychical disturbances. The irritation exerted upon the centre, as shown by Eckhard, is transmitted to the blood-vessels of the penis through the sacral nerves, and causes a marked dilatation of them. Through the great hypenemia of the three spongy bodies (corpora cavernosa bulbi and corpus cavernosus urethrte) the male member is markedly enlarged, as sumes a rigid condition, and is directed upwards: erection. This process is made possible, because a relaxation of the tonic contraction of the ves sels, caused by the previously mentioned nervous influence, allows of a greater blood-supply, and coincidently by compression of the veins, the return flow of the blood from the spongy spaces is hindered. This hin drance to the return flow of blood is to a great extent to be attributed to a contraction of the striated muscular tissue, which surrounds the root of the penis, and is caused by this same nervous influence.
This change in the penis makes it possible for it to enter into the female genitals. But it is only after a further irritation, caused by these parts, that the transmission of the semen into the vagina occurs. This
irritation is produced by the friction of the penia against the walls of the female genital canal. The irritation is.carried to the centre of the sexual function from the whole surface of the penis, but principally from the very sensitive glans penis, chiefly by the pudic nerve, and thereby con tractions of the spermatic ducts are inaugurated. Hereby the semen is moved forward in this canal, is further mixed with the secretions of the above-mentioned glands, and is forced through the ejaculatory duct into the urethra. At the same time, there also occurs, and probably with similar effect, a contraction of the dartos and cremasters. Then con tractions of the muscular tissue, the prostatic and membranous portion of the urethra occur, which advance the semen, whereupon the rhythmic contractions of the bulbi-cavernous and ischio-cavernosi muscles follow whereby the semen is completely and forcibly ejaculated from the urethra into the vagina. The 'pushing movements of the penis, inaugurated after its introduction into the vagina, are probably not for the purpose of deeper penetration. They produce friction between the dorsal surface of the penis and the swollen clitoris, whereby the voluptuous sensations of both individuals are increased, and the secretions are more rapidly ejaculated: the secretion of tbe vulvar glands in the female, and the ejac ulation of the semen in the male. As regards the part played in this act by- the external female genitals, it is certain that the excretion of the rulco-glandular secretion is without any physiological significance; on the contrary, I believe that the contraction of the constrictor ennui and perhaps also the anterior portion of the levator ani, which grasp the penetrating penis, is rightly so regarded, if we attribute to these muscles the function of binding organs. In apathetic women (of whom we shall speak later on), as well as in women who have repeatedly borne children, this contraction is only a partial one, and is in fact often entirely lacking, wnhout the coition being thereby influenced.