Although plants and animals have no peculiar elements; though the materials from which their bodies spring, and to which they return, are common earth, water, and air, yet in them these elements are wrought into something widely different from any form of lifeless mineral matters, under the influence of what is usually termed the principle of life. This may be said to consist of a favorable condition brought about by the union of certain elements, under a moist atmosphere and a high temperature, combined with other powerful forces in nature. "When this terrestrial globe began to cool the matter predominating in the atmosphere was water or its elements oxygen and hydrogen, carbonic acid and nitrogen; under the influence of a high temperature, and powerful sources of electricity, numerous combinations were produced between the elements; first carburetted hydrogen, then a nitrogenous combination, more or less analogous to the albuminous matter which we know" (Huxley). Among the innumerable combinations nature produced, during a series of infinite ages, slowly undergoing transformation, the mixture of these substances, acting chemically upon one another, generating and regenerating at the expense of their surroundings, composed the first living being. This being was of excessive simplicity, comparable to the organisms which we call monera. The sun's heat acting upon these elements, and the elements acting upon one another, produced motion. Heat is motion, expansion, restrained and acting in its strife upon the smallest particles of bodies.