Onanism, _coitus interruptus_, or withdrawal before ejaculation, which takes place _extra vas_, is intended to prevent impregnation. In the normal sexual act the male genital tract suddenly becomes congested with blood through nervous action of centres in the lumbar cord and the cerebrum. Cowper's and Littré's glands secret an alkaline fluid which neutralizes the acid urine in the urethra and thus prevents killing of the spermatozoa. Muscular peristaltic action presses out the spermatozoa and the secretions of the seminal vesicles and the prostate. When the act is normal there is a complete emptying of the tract of semen and of the blood engorgement; in _coitus interruptus_ there is incomplete ejaculation and only partial deplethorization. The seminal vesicles remain distended, and this distention, with the congestion of the prostate, causes continual excitation of the sexual centres without relief. There is irritability and exhaustion of the centres, and this state brings on premature ejaculation and final _impotentia coeundi_. Other common effects are tenesmus of the urinary bladder, incontinence of urine, nocturnal pollutions, sexual neurasthenia, pain in the legs, over the eyes, and in almost any part of the body, general weakness, headache, vertigo, cardiac palpitation, neurotic dyspepsia, and a train of psychic symptoms which not seldom end in suicide. In the woman there is the like blood engorgement and a pouring out of the secretions of Bartholin's and the other glands, but deplethorization takes place later in the woman than in the man, and for this reason the woman suffers more from _coitus interruptus_ than the man does. In onanism, as in masturbation, after the diseased conditions have been established it is extremely difficult to induce the patient to resist the almost overwhelming irritation. The canonists have interpreted the text of Sixtus V. to the effect that the eunuch is impotent precisely and solely because he cannot produce semen "_elaboratum in testibus_." No man produces semen _elaboratum in testibus_--more than 93 per cent. of the semen is produced entirely outside the testicle; nothing but the spermatozoa and two or three drops of a lubricating fluid are produced in the testicles. The eunuch really is impotent because the removal of the testicles and their nervous system so breaks the genital circuit, which consists of at least seventeen distinct parts, that erection is prevented, the formation of spermatozoa is impossible, the secretion of the essential vehicle of the sperm and of the fluids which render it fertile is cut off. The eunuch cannot penetrate and he cannot form any semen; he is impotent; the vasectomized man can penetrate, and he forms a semen which is sterile. I think now the vasectomized man is really impotent for the reason that I think the _mulier excisa_ is impotent, but he is not impotent because of the constitution of Sixtus V., which is not relevant at all to his case.