Nature keeps an exact account with all her children, and gives power in proportion to their fulfilment of her conditions. She measures out and sustains vital force according to the kind and fitness of the raw material provided for her. When we deal liberally with her, she deals liberally with us. For everything we give to her she makes a just return. The stomach, the nutrient arteries, the lungs, have no love, no patriotism, no pity; but they are perfectly honest. The healthy digestive organs will extract and pay over to the blood-vessels just so much of the nutritive elements as the food we eat contains in an extractible form, and no more; and for this purpose they will demand and take just so much of the nervous energy as may be needed. The nutrient arteries will convert into living flesh just so much of the nutritive elements as the digestive organs give them, and no more. The lungs will send out from the body as many of the atoms of exhausted and dead flesh as the oxygen we give them will convert into carbonic acid and water, and this is all they can do. In these matters, the vital organs are as honest and as faithful as the boiler, that gives forth steam in the exact ratio of the heat which the burning fuel evolves and the fitness of the water that is supplied to it; and neither can be persuaded to do otherwise. The living machine of bone and flesh and the dead machine of iron prepare their forces according to the means they have, not according to the ulterior purpose to which those forces are to be applied. They do this alike for all. They do it as well for the sinner as for the saint,--as well for the traitorous Secessionist striving to destroy his country as for the patriot endeavoring to sustain it. In neither case is it a matter of will, but of necessity. The amount of power to be generated in both living and dead machines is simply a question of quality and quantity of provision for the purpose. So much food, air, protection given produce so much strength. A proposition to reduce the amount of either of these necessarily involves the proposition to reduce the available force. Whoever determines to eat or give his men less or poorer food, or impure air, practically determines to do less work. In all this management of the human body, we are sure to get what we pay for, and we are equally sure not to get what we do not pay for.