Fear : Psychological Study of the Causes and Effects

What are the causes and effects of fear among human and all beings capable of feeling it? What are the signs of fear and the physical phenomena that accompany it?
Fear acts in two ways. At times it paralyzes and makes motionless; at other times it excites and gives extraordinary strength.
Fear is, finally, a protection against death. But salutary as it is, and inspired by nature, the feeling is one that must be energetically contended against, because it is an emotion of the lower class which it is necessary to try to dominate and make submissive to the moral conditions of our existence. We should try to conquer ourselves, and replace the notions of terror by the higher ideas which will perhaps triumph over fear, of self-forgetfulness, abnegation, duty.