10. IGNORANCE BEFORE MARRIAGE.--At some time before marriage those who are to enter into it ought to be made acquainted with some of the plainest common-sense limitations which should govern their new relations to each other. Ignorance in such matters has caused an infinite amount of disgust, pain, and unhappiness. It is not necessary to specify particulars here: see other portions of this work. * * * * * {269} Impregnation. [Illustration: A HEALTHY MOTHER.] 1. CONCEPTION OR IMPREGNATION.--Conception or impregnation takes place by the union of the male sperm and female sperm. Whether this is accomplished in the ovaries, the oviducts or the uterus, is still a question of discussion and investigation by physiologists. 2. PASSING OFF THE OVUM.--"With many woman," says Dr. Stockham in her Tokology, "the ovum passes off within twenty-four or forty-eight hours after menstruation begins. Some, by careful observation, are able to know with certainty when this takes place. It is often accompanied with malaise, nervousness, headache or actual uterine pain. A minute substance like the white of an egg; with a fleck of blood in it, can frequently be seen upon the clothing. Ladies who have noticed this phenomenon testify to its recurring very regularly upon the same day after menstruation. Some delicate women have observed it as late as the fourteenth day." 3. CALCULATIONS.--Conception is more liable to take place either immediately before or immediately after the period, and, on that account it is usual when calculating the date at which to expect labor, to count from the day of disappearance of the last period. The easiest way to make a calculation is to count back three months from the date of the last period and add seven days; thus we might say that the date was the 18th of July; counting back brings us to the 18th of April, and adding the seven days will bring us to the 25th day of April, the expected time.