Page:Popular Science Monthly Volume 24.djvu/602

584 facts, we should be near to an understanding of the difference between a high and a low organism; the life is high when there is a high degree of correspondence with a highly complex environment.

Poets have understood this principle better, perhaps, than physiologists.

"Who has no inward beauty none perceives, Though all around is beautiful"—

says Wordsworth; and Coleridge—

". . .We receive but what we give; And in our lives alone does Nature live!"

Emerson also embodies this whole philosophy in a single illustration: "The sea drowns both ship and sailor, like a grain of dust, and we call it fate; but let him learn to swim, let him trim his bark, and the water which drowned it will be cloven by it and will carry it like its own foam—a plume and a power."

When we remember that our environment consists, not only of the natural elements of earth and sky, reaching to the most distant star which communicates its vibrations to our atmosphere, but that it also includes other human beings with the influences which such an environment involves, we realize that, while physiology undoubtedly rests on chemistry and physics, it also includes psychology and reaches far toward sociology—sciences which involve the highest problems of our existence; and, though we find it impossible to sink our plummet to the depths of this ocean, or to send an arrow to the stars which gem the arching dome above, we may at least hope to gather a few shells on the shore of the one, and to intercept some gleams of light from those distant suns which fascinate by their very distance, and make glorious the night of our intellectual darkness even.

How, we next inquire, does the human embryo differ, at the progressive stages of its evolution, from the embryos of the various lower types which it successively resembles? Whence the impulse of development by which it rises from these lower levels to the human plane? In reply to these questions we can only refer to the principle of heredity which, though it imprints upon the germ no trace discoverable by any known test, unfailingly molds the plastic protoplasm into certain prescribed and prearranged forms, with their accompanying capacities and powers. The inherent forces by which one germ develops into an oak and another into a trailing vine, one into a mollusk and another into a man, are handed down from generation to generation, so that each plant and animal reproduces its own kind and not some other kind. This can not be regarded, however, as an exceptional fact; the production of the germ with all its hidden possibilities, like every other differentiation of matter, depends upon the general principle known as the persistence of force; and to deny that the power of development of any grade of life is inheritable is to deny the