But in all _normal_ cases, the ovum only passes into the womb once in every twenty-eight days; and, as a rule, it only remains in the womb for about half that period of time, that is, for about 14 or 15 days in each month. And so, since the menstrual flow ceases after about five days from its beginning, in about ten days _after_ its stopping, the ovum will have passed out of the womb, and hence that organ contains nothing that is impregnable. Under these conditions, semen may be deposited in the womb, without danger of impregnation. This is a simple proposition, and easy to understand if once known. However, it must be said that these _generally_ common conditions _do not always obtain_--that is, they are _not_ true in the case of _all_ women. There are women who will conceive at _any_ time in the month, if they are given a chance to do so. The physiological reason for such possibility is said to be this: There are always ova in the ovaries, in varying stages of development. Ordinarily, only once a month do any of these pass down into the womb; but, in exceptional cases, sometimes these ova are so partially held in the ovaries that, under the excitement of coitus, and because all these parts dilate so much during the act, an ovum may slip its moorings, under such conditions, pass down into the uterus at an untimely season, meet the semen there, and pregnancy result. Such are the facts _in some cases_. How, then, can a husband and wife tell how it is, or will be, in _their_ particular case? The answer is that they can only tell by trying, and that should be done as follows: The _first_ sexual meeting of the bride and groom should _never_ take place until at least _ten days after the ceasing of the menstrual flow in the bride! This is a rule that should never be violated_ if the parties wish to "_test out_" the real condition as to whether or not the bride has any "free time." The chances are several to one that she _has_ such leeway; but the fact can only be established by "proving up" and this can _never_ be done if any _chances_ are taken. Put this down as rule number one. For this reason, it is well for the bride to fix the wedding day; and, if possible, for her to locate it sometime during the probably immune period. And the nearer she can bring this day to the _beginning_ of such period of freedom from danger of pregnancy, the better. For, if it should happen that the first coitus should take place only a _day or two before_ the time when another "monthly" was due, such excitement might hasten the passage of the nearly-ripe ovum into the uterus, and conception might occur. In which case, "all the fat would be in the fire," nothing would be proved, and the parties would be as ignorant as ever regarding the facts in _their_ case.