20. "OVER-INDULGENCE in intercourse," says Dr. Hoff, "is sometimes the cause of barrenness; this is usually puzzling to the interested parties, inasmuch as the practices which, in their opinion, should be the source of a numerous progeny, have the very opposite effect. By greatly moderating their ardor, this defect may be remedied." 21. "NAPOLEON AND JOSEPHINE.--A certain adaptation between the male and female has been regarded as necessary to conception, consisting of some mysterious influence which one sex exerts over the other, neither one, however, being essentially impotent or sterile. The man may impregnate one woman and not another, and the woman will conceive by one man and not by another. In the marriage of Napoleon Bonaparte and Josephine no children were born, but after he had separated from the Empress and wedded Maria Louisa of Austria, an heir soon came. Yet Josephine had children by Beauharnais, her previous husband. But as all is not known as to the physical condition of Josephine during her second marriage, it cannot be assumed that mere lack of adaptability was the cause of unfruitfulness between them. There may have been some cause that history has not recorded, or unknown to the state of medical science of those days. There are doubtless many cases of apparently causeless unfruitfulness in marriage that even physicians, with a knowledge of all apparent conditions in the parties cannot explain; but when, as elsewhere related in this volume, impregnation by artificial means is successfully practised, it is useless to attribute barrenness to purely psychological and adaptative influences." * * * * * PRODUCING BOYS OR GIRLS AT WILL. 1. CAN THE SEXES BE PRODUCED AT WILL?--This question has been asked in all ages of the world. Many theories have been advanced, but science has at last replied with some authority. The following are the best known authorities which this age of science has produced. 2. THE AGRICULTURAL THEORY.--The agricultural theory as it may be called, because adopted by farmers, is that impregnation occurring within four days of the close of the female monthlies produces a girl, because the ovum is yet immature; but that when it occurs after the fourth day from its close, gives a boy, because this egg is now mature; whereas after about the eighth day this egg dissolves and passes off, so that impregnation is thereby rendered impossible, till just before the mother's next monthly.--_Sexual Science._ 3. QUEEN BEES LAY FEMALE EGGS FIRST, and male after wards. So with hens; the first eggs laid after the tread give females, the last males. Mares shown the stallion late in their periods drop horse colts rather than fillies.--_Napheys._ 4. IF YOU WISH FEMALES, give the male at the first sign of heat; if males, at its end.--_Prof. Thury._