_The Birth Rate Small among the Upper Classes in Society._--In most countries it is the well-to-do classes that have small families and the poor that have large ones. It is from the interpretation of this fact that we can derive a most important modification of the Malthusian law. It is the voluntary conduct of different classes which determines whether the birth rate shall be large or small; and the fact is that in the case of the rich it is small, in the case of the poor it is comparatively large, while in the case of a certain middle class, composed of small employers, salaried men, professional men, and a multitude of highly paid workers, it is neither very large nor very small, but moderate. In a general way the birth rate varies inversely as the earning power of the classes in the case, though the amounts of the variations do not correspond to each other with any arithmetical exactness. If one class earns half as much per capita as another, it does not follow that the families belonging to this class will have twice as many children. They do, on the average, have more children. There is, then, at least an encouraging probability that promoting many men from the third class to the middle class would cause them to conform to the habit of the class they joined. This class is at present largely composed of persons who have risen from the lowest of the classes, and any future change by which the third class becomes smaller and the second larger would doubtless retard the average birth rate of the whole society.