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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
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