The older a woman is at the time of her marriage, the longer deferred is the age at which she naturally becomes sterile. She bears children later in life, in order to compensate, as it were, for her late commencement. But although she continues to have children until a more advanced age than the earlier married, yet her actual child-bearing period is shorter. Nature does not entirely make up at the end of life for the time lost from the duties of maternity in early womanhood; for the younger married have really a longer era of fertility than the older, though it terminates at an earlier age. A wife who, having had children, has ceased for three years to conceive, will probably bear no more, and the probability increases as time elapses. After the first, births take place with an average interval, in those who continue to be fertile, of about twenty months. Nursing women are generally sterile, above all, during the first months which follow accouchement, because the vital forces are then concentrated on the secretion of the milk. In a majority of instances, when suckling is prolonged to even nineteen or twenty months, pregnancy does not take place at all until after weaning. Climate has also an influence upon the fertility of marriages. In southern regions more children are born, fewer in northern. The number of children is in inverse proportion to the amount of food in a country and in a season. In Belgium, the higher the price of bread the greater the number of children, and the greater the number of infant deaths. The seasons exert a power over the increase of population. The spring of the year, as has already been stated, is the most favourable to fecundity. It is not known whether day and night have any effect upon conception. The worldly condition seems to have much to do with the size of a family. Rich and fashionable women have fewer children than their poor and hard-worked neighbours. Wealth and pleasure seem to be often gladly exchanged for the title of mother.