‘Dead’ matter has two forms of inertia—that of rest (mass), and that of motion (momentum) —and it seems to me that living matter possesses a property, not hitherto recognised as such, which might be called functional inertia, or metabolic inertia of protoplasm whether animal or vegetable. It is owing to the inertia of matter at rest that the heavy gate, swung even on almost frictionless hinges, cannot be instantaneously set in motion; and when it has been set swinging, it is owing to its inertia of motion (momentum) that it continues to swing for some time after we have ceased to push it. By functional inertia of protoplasm I mean the power or property of protoplasm to remain in the metabolic status quo ante; if resting—anabolising—to remain doing so, even after the reception of a stimulus tending to bring about the opposite metabolic state, this might be called anabolic inertia; if active—katabolising—to remain so even after the reception of a stimulus tending to induce anabolism, or after the cessation of the stimulus that elicited the activity—katabolic inertia or functional momentum. Functional inertia is the power or property which bioplasm has of maintaining its functional status quo for a longer or shorter time according to the function considered; it is that power of continuing to exhibit the particular phenomena it has been exhibiting even after the death of the organism of which it is a constituent.