Now fertilisation does not necessarily occur whenever the male organ comes in contact with the female organ.  Fertilisation occurs only when a male-cell (spermatazoon) unites with a female-cell (ovum); in other words, when the spermatazoa in the seminal fluid of a man meet and unite with the germ or ovum in the body of a woman.  That is the beginning of the child.  This union of the two cells need not take place during or immediately after sexual intercourse.  It may occur many hours, or even two or three weeks, after connection, because the spermatazoa have motion of their own.  They are tiny threadlike bodies, which may work their way towards the ovum long after they have left the body of the man and been placed in the body of the woman, and the uterus has a searching movement, and may by its pulsations draw the spermatazoa upwards.  For these reasons a woman cannot be quite sure of the exact time of fertilisation, and hence cannot predict exactly the date of the child-birth.  Generally the pregnancy lasts nine months, but it may last longer—­say ten months on rare occasions; and it may be extended apparently by a delay in fertilisation.

PREVENTION OF CONCEPTION.

For many reasons which I need not enumerate here, the precautions against impregnation can most easily and effectively be taken by the woman, rather than by the man.  She is the one fertilised, and therefore she is the one to guard herself against fertilisation.

There are two methods of preventing fertilisation:—­

     (1) The chemical method, that is, the destruction of the male
     cells (spermatazoa) by means of a suitable germicidal substance,
     such as many of the disinfectants; and

     (2) The mechanical method, that is, the adoption of measures
     which keep the male and the female cells apart from one another.

[Illustration:  INNER SIDE OF THIGH.

DIAGRAM 1.—­Female organs of generation in normal condition.  This shows diagrammatically the position of the organs if a woman were cut in two between the thighs.  The rubber pessary is shown in position, slightly distending upper end of vagina (or front passage), and covering the opening into interior of womb.  A suppository introduced beforehand will dissolve and occupy the dotted space above rubber pessary, forming a pool around the mouth of the womb.  The walls of the vagina are elastic and collapsible.  Infection with gonorrhoea may occur in the female urethra (or water passage) or in the vagina, etc.  Syphilis may infect internal and external parts of female organs; also breasts, mouth, tongue, etc., and other openings of the body.]