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130 used up, while the other set was probably produced by muscular activity. It is also well known that very complex bodies containing nitrogen are found in extracts of muscle, and it is highly probable that these are in a way waste products—substances that have resulted from the breaking down of the matter of the muscle. These facts that I have laid before you all point one way. They all tell of chemical changes in muscle, and they all support the statement that the harder the muscle has to work, the greater is the activity of the chemical phenomena happening in it. Let us put this in more correct scientific language. The setting free of energy by the muscle,—as mechanical energy when it moves, and as heat when it becomes warm,—is associated with, and is likely the result of, the chemical processes happening in it.