owever important. Each single law stands
by itself, and exacts complete obedience to its own requirements: it
gives its own rewards and inflicts its own punishments. The stomach will
not digest tough and hard or old salted meats, or heavy bread, without
demanding and receiving a great and perhaps an almost exhausting
proportion of the nervous energies. The nutritive organs will not create
vigorous muscles and effective limbs, unless the blood is constantly and
appropriately recruited. The lungs will not decarbonize and purify the
blood with foul air, that has been breathed over and over and lost its
oxygen. However noble or holy the purpose for which human power is to be
used, it will not be created, except according to the established
conditions. The strength of the warrior in battle cannot be sustained,
except in the appointed way, even though the fate of all humanity depend
on his exertions.

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 al