character of the different parts of which it is composed, but of the relations of these parts to each other. The force operating such a machine may be derived from a simple fall of water, or from the oxidation of burning anthracite; but, although this may be the sole source of the actual energy expended, it is far from being the only factor concerned in the production of the special kind of work accomplished. The results are due to the transformations of this initial force into force of other kinds, the character of the work done depending on the peculiar construction of the machine—in other words, on the relations of its parts. Thus the expansive power of steam may be expended in the idle clapping of the lid of a tea-kettle, or in the driving of the piston in the engine of an ocean-steamer, according to the relations into which the steam is brought. Keeping this illustration in mind, we may perhaps attain to some conception of the meaning of a living organism, and wherein consist the differences in different organisms.
The life-processes are concerned in the building up of the tissues—that is, in the construction and constant repair of the mechanism out of materials supplied by food; coincident with this assimilation of new material, there is a corresponding accumulation of energy or force. The energies liberated, on the other hand, in the activities of muscle, nerve, brain, etc., come from the oxidation—the so-called waste—of these tissues; and (as in the machine) the results produced are due to the transformations of this initial force, derived from oxidation of the tissues, into other kinds of force, viz., those manifested by living animal organisms, the character of the work done depending (as in the illustration) on the particular construction of the mechanism concerned. In the operations of living organisms, not less than in those mechanisms whose motive power is derived from steam, not a known law of matter is violated, but all are wrought into a harmony so complete that the entire complex and heterogeneous structure acts as a unit.
Glancing in thought over the vast expanse of matter of which the universe consists, what has been the direction of the progress witnessed through the long ages since the beginning condensation of the nebulous masses in which our solar system is believed to have originated? The immense globes which whirl in repeated circles through the heavenly spaces, though bound together by the strongest and most subtile bonds, roll blindly on, forever unconscious of themselves and of one another. The lily of the field even, clothed in beauty though it be, and surrounded by the greater glories of earth and sky—the warm sunshine and green fields—has no conscious enjoyment of itself or of them; but as elements identical with those which compose these unconscious forms have combined and recombined in compounds of increasing complexity, as molecules have condensed and differentiated in the development of a higher kind of living matter, consciousness has dawned, and (mainly through the avenues of the special senses) mind