s it were, stored up in a countless variety of
ways, and reserved for future action; and, when finally released, the whole
amount may be set free at once, so as to expend itself in a single impulse,
as in case of the arrow or the bullet; or it may be partially restrained,
so as to expend itself gradually, as in the case of a clock or watch. In
either case the total amount expended will be precisely the same--namely,
the exact equivalent of that which was placed in store.

_Vegetable and Animal Life_.

There are a vast number of mechanical contrivances in use among men for
thus putting force in store, as it were, and then using it more or less
gradually, as may be required. And nature, moreover, does this on a scale
so stupendous as to render all human contrivances for this purpose utterly
insignificant in comparison. The great agent which nature employs in this
work is vegetation. Indeed, it may truly be said that the great function
of vegetable life, in all the infinitude of forms and characters which it
assumes, is to _receive and store up force_ derived from the emanations of
the sun.

Animal life, on the other hand, exists and fulfills its functions by
the _expenditure_ of this force. Animals receive vegetable productions
containing these reserves of force into their systems, which systems
contain arrangements for liberating the force, and employing it for the
purposes it is intended to subserve in the animal economy.

The manner in which these processes are performed is in general terms as
follows: The vegetable absorbs from the earth and from the air substances
existing in their natural condition--that is, united according to their
strongest affinities. These substances are chiefly water, containing
various mineral salts in solution, from the ground, and carbonic acid from
the air. These substances, after undergoing certain changes in the vessels
of the plant, are exposed to the influence of the rays of the sun in the
leaves. By the power of these rays--including the calorific, the luminous,
and the actinic--the natural affinities by which the above-mentioned
substances were united are overcome, and they are formed into new
combinations, in which they are united by very weak affinities. Of course,
they have a strong tendency to break away from the new unions, and fall
back into the old. But, by some mysterious and incomprehensible means,
the sun has power to lock them, so to speak, in their new forms, so as to