There is a popular idea, chiefly among women, that while the mother is nursing sexual intercourse may be indulged in with impunity; and the surprise with which women are frequently cured of the belief is very great indeed. The excitement of the act in the woman, as before stated, ripens and throws off an egg from the ovary, and impregnation follows. The nerve force which is manifested usually in the sexual processes, however, being in a measure centered upon lactation, masks the usual manifestations of menstruation, and makes it impossible to determine when the ovum has ripened, so that impregnation is more insidious than at other times, but none the less certain.