Life. The great characteristic of plants and animals is life, which these beings enjoy, but minerals do not. We may safely infer that life is not a product, or result, of the organization; but is a force manifested in matter, which it controls and shapes into peculiar forms--into an apparatus, in which means are manifestly adapted to ends, by which results are reached that are in no other way attainable. As we rise in the scale of organized structure from plants through the various grades of the animal organization, the superadded vital manifestations become more and more striking and peculiar. But the fundamental characteristics of living beings--those which all enjoy in common, and which necessarily give rise to all the peculiarities above enumerated--are reducible to two, viz.: 1. The power of self-support, that of nourishing themselves by taking in surrounding mineral matter and converting it into their own proper substance; by which individuals increase in bulk or grow, and maintain their life; 2. The power of self-division or reproduction, by which they increase in number and perpetuate the species. A striking illustration may set both points in a strong light. The larva of the flesh-fly possesses such power of assimilation that it will increase its own weight two hundred times in twenty-four hours, and such consequent power of reproduction that Linnæus did not exaggerate when he affirmed that "Three flesh-flies would devour the carcass of a horse as quickly as a lion." The distinction between vegetable and mineral is therefore well defined. But the line of demarcation between plants and animals is by no means so readily drawn. Ordinarily, there can be no difficulty in distinguishing a vegetable from an animal. All the questionable cases occur on the lower confines of the kingdom, which exhibit forms of the greatest simplicity of structure, and of a minuteness of size that baffles observation. Even here the uncertainty may be attributed rather to the imperfection of our knowledge, than to any confusion of the essential characteristics of the two kinds of beings (the kingdom of Protista above alluded to). The essential characteristics of vegetables doubtless depend upon the position which the vegetable kingdom occupies between the mineral and the animal, and upon the general office it fulfills.