Page:Popular Science Monthly Volume 43.djvu/531

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515
HOW PLANTS AND ANIMALS GROW.

organs of the same individual? We can not attribute them to organization or structure, as so far as we know these are the result of vital activities, and can not, therefore, be the cause. As forcibly stated by Prof. Huxley in his paper on the cell theory (1852), cells "are no more the producers of the vital phenomena than the shells scattered in orderly lines along the sea-beach are the instruments by which the gravitative force of the moon acts upon the ocean. Like these, the cells mark only where the vital tides have been and how they have acted."

It has been suggested that the various factors in nutrition, including even "structure" and "composition," must be looked upon as modes of motion in accordance with the concepts of modern physics, and from this point of view the body of a man has been compared to a fountain. "As the figure of the fountain remains the same, though fresh water is continuously rising and falling, so the body seems the same, though fresh food is always replacing the old man, which in turn is always falling back to dust. And the conception which we are urging now is one which carries an analogous idea into the study of all molecular phenomena of the body."

The pertinence and significance of these physical considerations should not, however, lead us to assume that life is but a form of energy. We can not doubt that energy is the motive power in living beings, and that its transformations and activities which are evident in all organic processes are properly-considered as modes of motion, but we must discriminate between the motive power that does the work and the directing force which guides it in the lines along which it acts and determines the results produced. We are unable to detect any difference in the potential energy of living and of dead protoplasm, but we recognize an immense difference in their significant properties—a difference so wide that life can not be defined as a form of energy.

The manifestations of energy in organic processes are readily perceived, and there are definite standards with which to measure them, but our most delicate means of research throw no light on the purely vital endowments of protoplasm, which not only direct and control its activities, but are transmitted in well-defined characters from parent to offspring. There is no life without preexisting life from which it is derived, and the physical basis through which it acts, or is made manifest, furnishes no satisfactory explanation as to its real essence and constitution.

In discussing the economies of foods and diets, if we keep in mind the significant facts that vital activities direct and determine the transformations of energy and the collocations of matter in plants and animals, in accordance with the nutritive requirements of every organ and tissue, and that in the higher animals