Page:Popular Science Monthly Volume 20.djvu/634

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dead tree, so we now perceive a host of animals growing out of the ruin of their dead predecessor. What is not otherwise devoured serves as a receptacle for the eggs of insects, and it soon swarms with grubs and maggots, destined eventually to sail in winged lightness in the air, without a hint in their aërial grace that their floating life had this unpleasant source.

And they shall be eaten—and their eaters eaten; and thus the organic world, which grew up by this devouring process from the smallest plant to man, slowly drops back by form after form through the lower world of animals and plants, until every grain of vitality is sucked out of it, and it falls at last, utterly juiceless and lifeless, into the mineral world from which it came.

Such is Nature's most striking economy. Such the work she gets from the subscriptions from the lower world, ere they are paid back into the treasury whence they were drawn. They form the coin of life, passing from hand to hand, and abraded by every touch, until utterly worn away, and needs to be replaced by new coins from the organic mint.

And there is yet another feature in this round of economies with which we may safely close our review. Nature not only provides us with new food, but makes our old nutriment do duty again and again, ere every possibility of use is squeezed out of it. Thus the nitrogenous material of the body, which is thrown into the circulation by waste of the muscles, does not appear to be at once carried out of the body as useless refuse. It is too precious to be so lightly thrown away. On the contrary, it is probably worked over again in the blood, a portion of it becoming mineral matter, and yielding force to lift another portion into the condition of nutriment. A similar process of reemployment of nitrogenous material takes place in vegetables. Thus, a part of the coin is worn off, and the remainder paid back into the bank of life for its existing value. And so it may be paid back again and again, until it is all lost in this successive wear and tear, and the mineral world gets its own again.

This is Nature's thrifty housekeeping. Not an ounce of force is wasted. All the possible life in organic material is worked out of it ere it can escape. And even those vegetable forms that have avoided this process by being turned into stone have but temporarily locked up their forces, which flow out eventually in the form of light and heat, to invigorate, vivify, and gladden the world of living beings.