Inanimate nature seems governed by definite laws; that is, given the same conditions, the same results always follow. The reactions between two chemical elements under the same conditions are always the same. The physical forces go their unchanging ways, and are variable only as the conditions vary. In dealing with them we know exactly what to expect. We know at what degree of temperature, under the same conditions, water will boil, and at what degree of temperature it will freeze. Chance and probability play no part in such matters. But when we reach the world of animate nature, what a contrast we behold! Here, within certain limits, all is in perpetual flux and change. Living bodies are never two moments the same. Variability is the rule. We never know just how a living body will behave, under given conditions, till we try it. A late spring frost may kill nearly every bean stalk or potato plant or hill of corn in your garden, or nearly every shoot upon your grapevine. The survivors have greater powers of resistance--a larger measure of that mysterious something we call vitality. One horse will endure hardships and exposures that will kill scores of others. What will agitate one community will not in the same measure agitate another. What will break or discourage one human heart will sit much more lightly upon another. Life introduces an element of uncertainty or indeterminateness that we do not find in the inorganic world. Bodies still have their laws or conditions of activity, but they are elastic and variable. Among living things we have in a measure escaped from the iron necessity that holds the world of dead matter in its grip. Dead matter ever tends to a static equilibrium; living matter to a dynamic poise, or a balance between the intake and the output of energy. Life is a peculiar activity in matter. If the bicyclist stops, his wheel falls down; no mechanical contrivance could be devised that could take his place on the wheel, and no combination of purely chemical and physical forces can alone do with matter what life does with it. The analogy here hinted at is only tentative. I would not imply that the relation of life to matter is merely mechanical and external, like that of the rider to his wheel. In life, the rider and his wheel are one, but when life vanishes, the wheel falls down. The chemical and physical activity of matter is perpetual; with a high-power microscope we may see the Brunonian movement in liquids and gases any time and at all times, but the movement we call vitality dominates these and turns them to new ends. I suppose the nature of the activity of the bombarding molecules of gases and liquids is the same in our bodies as out; that turmoil of the particles goes on forever; it is, in itself, blind, fateful, purposeless; but life furnishes, or _is_, an organizing principle that brings order and purpose out of this chaos. It does not annul any of the mechanical or