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 *logical work. The excreta bear witness to a certain organic demolition. Generalizing this teaching of experiment the illustrious biologist divined the fundamental law of energetics before the idea of energetics had made much way in France. Every act which expends energy, which produces heat or motion, any manifestation whatever that may be looked upon as an energetic transformation, necessarily expends energy, and that energy is borrowed from the substance of the organism. These substances are simplified, broken up, and destroyed. Now the functional activity of the muscle produces heat and movement in warm-blooded as well as in cold-blooded animals. The functional activity of the glands produces heat, as has been shown by the celebrated experiments of C. Ludwig on the salivary secretion, and as is also shown by the study of thermal topography in the vertebrates. The functional activity of the nerves and the brain produces a slight quantity of electricity and heat, as most observers have agreed. The functional activity of the electrical and of the photic apparatus also expends energy. Finally, the eye which receives the photic impression destroys the purple matter of the retina, and that purple matter, as we well know, is recuperated in the dark during the repose of the organ. Everything that is expressed objectively, everything that is a phenomenon in the living being—with the exception of growth and formation, which are generally slow phenomena, and of which we can only get an idea by the comparison of successive states—all these energetic manifestations suppose a destruction of organic matter, a chemical simplification, the source of the energy manifested. And that is why material destruction does not merely