6 1 4 THE POPULAR SCIENCE MONTHLY. 



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 aerial grace that their floating life had 

 this unpleasant source. 



And they shall be eaten and their eaters eaten ; and thus the or- 

 ganic world, which grew up by this devouring process from the small- 

 est 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 nitroge- 

 nous 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 an- 

 other portion into the condition of nutriment. A similar process of re- 

 employment 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. 



