The simple reflex, immediate response to a stimulus, has only a limited field in human life or adult life. Sherrington points out in his notable book, "The Integrative Action of the Nervous System," that there is a play of the entire organism on each responding element, and there is also a competition throughout each pathway to action. Let us examine this a little closer. A man is hungry, let us say; i. e., there arise from his gastro-intestinal tract and from the tissues stimuli which arouse motor mechanisms to action and the man seeks food. The need of the body arouses desire in the form of an organic sensation and this arouses mechanisms whose function is to satisfy that desire. Let us assume that he finds something that looks good and he is about to seize it when an odor, called disagreeable, assails his nostrils from the food, which stops him. Then there arises a competition for action between the desire for food and the visual stimulus, associated memories, etc., on the one hand, and the odor, the awakened fear, memories, disgust, etc., on the other hand. This struggle for action, for use of the mechanisms of action, is the struggling of choosing, one of the fundamental phenomena of life. In order for a choice to become manifest, what is known as inhibition must come into play; an impulse to action must be checked in order that an opposing action can be effective. The movement of rejection uses muscles that oppose the movement of acquirement; e. g., one uses the triceps and the other the biceps, muscles situated in opposite sides of the upper arm and having antagonistic action. In order for triceps to act, biceps must be inhibited from action, and in that inhibition is a fundamental function of the organism. In every function of the body there are opposing groups of forces; for every dilator there is a contractor, for every accelerator of action there is inhibition. Nature drives by two reins, and one is a checkrein.