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 role 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.

=Repulsion and Disgust.= Akin to the instinct of flight is that of repulsion, which impels us, instead of fleeing, to thrust the object away.  It leads us to reject from the mouth noxious and disgusting objects and to shrink from slimy, creepy creatures, and has of course been highly useful in protecting the race from poisons and snakes.  It still operates in the tendency to put away from us those things, mental or physical, toward which we feel aversion or disgust.  Recent psychological discoveries have revealed how largely a neurosis consists in putting away from us—­out of consciousness,—­whatever we do not wish to recognize, and so it happens that disgust plays an unexpected part in nervous disorders.

=Curiosity and Wonder.= Fortunately for the race, it has not had to wait until different features of the environment prove to be helpful or harmful.  There is an instinct which urges forward to exploration and discovery and which enables the creature not only to adapt itself to the environment but to learn how to adapt the environment to itself.  This is the instinct of curiosity.  It is the impulse back of all advance in science, religion, and intellectual achievement of every kind, and is sometimes called “intellectual feeling.”