In short, while all through the vegetable and animal kingdoms the limit of subsistence is independent of the thing subsisted, with man the limit of subsistence is, within the final limits of earth, air, water, and sunshine, dependent upon man himself. And this being the case, the analogy which it is sought to draw between the lower forms of life and man manifestly fails. While vegetables and animals do press against the limits of subsistence, man cannot press against the limits of his subsistence until the limits of the globe are reached. Observe, this is not merely true of the whole, but of all the parts. As we cannot reduce the level of the smallest bay or harbor without reducing the level not merely of the ocean with which it communicates, but of all the seas and oceans of the world, so the limit of subsistence in any particular place is not the physical limit of that place, but the physical limit of the globe. Fifty square miles of soil will in the present state of the productive arts yield subsistence for only some thousands of people, but on the fifty square miles which comprise the city of London some three and a half millions of people are maintained, and subsistence increases as population increases. So far as the limit of subsistence is concerned, London may grow to a population of a hundred millions, or five hundred millions, or a thousand millions, for she draws for subsistence upon the whole globe, and the limit which subsistence sets to her growth in population is the limit of the globe to furnish food for its inhabitants. But here will arise another idea from which the Malthusian theory derives great support—that of the diminishing productiveness of land. As conclusively proving the law of diminishing productiveness it is said in the current treatises that were it not true that beyond a certain point land yields less and less to additional applications of labor and capital, increasing population would not cause any extension of cultivation, but that all the increased supplies needed could and would be raised without taking into cultivation any fresh ground. Assent to this seems to involve assent to the doctrine that the difficulty of obtaining subsistence must increase with increasing population.