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 CHAPTER II.

ENERGY IN BIOLOGY.

§ 1. Energy in Living Beings.—§ 2. The First Law of Biological Energetics:—All Vital Phenomena are Energetic Transformations.—§ 3. Second Law:—The Origin of Vital Energy is in Chemical Energy. Functional Activity and Destruction.—§ 4. Third Law:—The Final Form of Energetic Transformation in the Animal is Thermal Energy. Heat is an Excretum.

The theory of energy was thought of and utilized in physiology before it was introduced into physics, in which it has exercised such an extraordinary influence. Robert Mayer was a physicist and a doctor. Helmholtz was equally at home in physiology and in physics. From the outset both had seen in this new idea a powerful instrument of physiological research. The volume in which Robert Mayer expounded, in 1845, his remarkable views on organic movement in relation to nutrition, and Helmholtz' commentary leave us in no doubt in this respect. The essay on the mechanical equivalent of heat, of a more particularly physical character, is six years later than the earlier work.

The Relations between Energetics and Biology.—The theory of energy is therefore only returning to its cradle; and to that cradle it returns with all the sanction of physical proof, as the most general theory