to some degree irritable, all are capable of reproduction of their own kind of cells, and so on.
Thus, from the beginning of his career, as a microscopic speck of living matter, to its close, although he figures as the most highly endowed and transcendent of beings, man, biologically considered, is protoplasm, protoplasm, only protoplasm; and, whatever his perfections, regarded as a member of the animal series, he has the high privilege of knowing if not of feeling himself the brother of all living things. With Job, he may say unto the worm, "Thou art my mother and my sister." "Oh, why should the spirit of mortal be proud?"
"What, then, is protoplasm?" we are inclined to ask, almost at the close of our attempt at a description.
Professor Huxley has called it "the physical basis of life"—an expression which has become classic in the scientific world—while life, in its turn, is defined as a property, or congeries of properties, of protoplasm. Pflüger has naively said, "Albumen lives" that is, becomes protoplasm—"when it begins to take in oxygen"; and Foster, with equal simplicity, remarks, "The whole secret of life may almost be said to be wrapped up in the occult properties of certain nitrogen compounds."
Lewes, in his own graphic style, has said, "The organism and its environment are the two factors, of which life is the product."
Protoplasm is the agent by which the energy of non-living matter is converted into that of living matter—the sacred fire which is never permitted to go out, but perpetually glows on the altar of Nature, fed by the vestal forces of the environment, and burning ever higher and higher through those twin influences, heredity and the survival of the fittest.
This true "vital spark" is not only transmitted from generation to generation in the entire animal world, each reproducing its own kind, but it has been handed on, through vast geological ages, from branch to branch of the animal tree, since that far-off period when the "dawn animal" first left its imprint in the hardening mud of its slimy bed at the bottom of a vast ocean whose waters were still under the influence of the earth's heated interior, when this ocean was overhung by a sky dark with clouds so dense that day and night were scarcely distinguishable, and shutting in an atmosphere heavy with carbonic-acid gas.
The relations observed between the fossil animals thus far discovered, the existing animal series, and the embryonic forms of all animals at the various stages of development of their respective embryos, are most significant. The earliest, oldest known fossil (the Eozoön Canadense, or "dawn-animal," the genuineness of which, though denied by some, is more than probable) belongs to the same class of organisms as the moneron and the amœba of to-day, which stand at the bottom of the scale of animal life; and the geological ladder in its ascent bears upon its successive rounds fossils which correspond, with
