We fear not in our hearts alone, not in our brains alone, not in our viscera alone--fear influences every organ and tissue. Each organ or tissue is stimulated or inhibited according to its use or hindrance in the physical struggle for existence. By thus concentrating all or most of the nerve force on the nerve-muscular mechanism for defense, a greater physical power is developed. Hence it is that under the stimulus of fear animals are able to perform preternatural feats of strength. For the same reason, the exhaustion following fear will be increased as the powerful stimulus of fear drains the cup of nervous energy even though no visible action may result.... Perhaps the most striking difference between man and animals lies in the greater control which man has gained over his primitive instinctive reactions. As compared with the entire duration of organic evolution, man came down from his arboreal abode and assumed his new rôle of increased domination over the physical world but a moment ago. And now, though sitting at his desk in command of the complicated machinery of civilization, when he fears a business catastrophe his fear is manifested in the terms of his ancestral physical battle in the struggle for existence. He cannot fear intellectually, he cannot fear dispassionately, he fears with all his organs, and the same organs are stimulated and inhibited as if, instead of its being a battle of credit, or position, or of honor, it were a physical battle with teeth and claws.... Nature has but one means of response to fear, and whatever its cause the phenomena are always the same--always physical.[9] [Footnote 9: Crile: _Origin and Nature of the Emotions_, p. 60 ff.] * * * * * The moral is as plain as day: Learn to call up fear only when speedy legs are needed, not a cool head or a comfortable digestion. Fear is a costly proceeding, an emergency measure like a fire-alarm, to be used only when the occasion is urgent enough to demand it. How often it is misused and how large a part it plays in nervous symptoms, both mental and physical, will appear more clearly in later chapters.