involves the least expenditure of energy. In the case of inorganic movements there is no such economy, since those movements are mere effects, and comply unvaryingly with the laws of mechanics. Finally, the exertion of choice by an organism does not determine whether movement shall take place in the direction of the least resistance or not—for that is the inevitable mode of all movements, organic as well as inorganic—but whether the energy expended in the differential or greatest stress producing movement shall be a larger or a smaller quantity.
We have next to note that the economy of energy which is possible in organic movements has two forms. There is economy in the realm of the conscious will, exemplified in movements by which animals reach various ends; and there is an economy in the realm of the unconscious life of the organism by which the parts thereof rearrange themselves in such a way as to lessen the expenditure of effort in the work of maintenance. For, whenever function is imposed by the organism upon certain of its parts, such parts, moving into configurations of least resistance, set up the intelligent adaptations which we know as organs. The only difference between a tool and an organ is that the former has been consciously shaped by man, whereas the latter has arisen through the unconsciously effected rearrangements of living molecules upon which function has been imposed by the organism. All organs, like all tools, are paths of least resistance, ways of reaching ends of organic maintenance with a minimum expenditure of effort. Simultaneously, moreover, with the saving of energy spared through the gradual perfecting of organs, there goes on a gradual improvement of the ends which such organs are unconsciously produced to reach. For this is simply to say that all effort saved by an organism through increase of the efficiency of its organs and processes goes—the circumstances being favorable—to increase the complexity and delicacy of its relation to the environment, as well as to enlarge the scope of the activities of maintenance.
The way in which organic molecules move into configurations that offer the least resistance to their special activities may be seen in similar structural formations which are more or less unconsciously assumed by human beings. One of these is the habit of taking turn by people waiting, say, at the box office of a theatre—a configuration which is assumed more or less unconsciously, because it is the one which, under the whole of the circumstances, involves conditions of least resistance. There is a similar selection of conformations involving a maximum of ease in the manner in which pedestrians avoid collision with each other. The throng in movement on the crowded sideways of a great city divides itself naturally and without conscious delibera-
