Hunger. Hunger is the most pressing desire of the egoistic or self-preserving impulse. The yearning for food and the impulse to seek and eat it are aroused organically within the body and are behind much of the activity of every type of life. As the impulse is so familiar, and its promptings are so little subject to psychic control, it seems unnecessary to do more than mention its importance.
Flight and Fear. All through the ages the race has been subject to injury. Species has been pitted against species, individual against individual. He who could fight hardest or run fastest has survived and passed his abilities on to his offspring. Not all could be strongest for fight, and many species have owed their existence to their ability to run and to know when to run. Thus it is that one of the strongest and most
universal tendencies is the instinct for flight, and its emotion, fear. "Fear is the representation of injury and is born of the innumerable injuries which have been inflicted in the course of evolution." [8] Some babies are frightened if they are held too loosely, even though they have never known a fall. Some persons have an instinctive fear of cats, a left-over from the time when the race needed to flee from the tiger and others of the cat family. Almost every one, no matter in what state of culture, fears the unknown because the race before him has had to be afraid of that which was not familiar.
[8] ] Crile: Origin and Nature of the Emotions.
The emotion of fear is well known, but its purpose is not so often recognized. An emotion brings about internal changes, visceral changes they are called, which enable the organism to act on the emotion,—to accomplish its object. There is only so much energy available at a given moment, stored up in the brain cells, ready for use. In such an emergency as flight every ounce of energy is needed. The large muscles used in running must have a great supply of extra energy. The heart and lungs must be speeded up in order to provide oxygen and take care of extra waste products. The special senses of sight and hearing must be sensitized. Digestion and intestinal peristalsis must be stopped in order to save energy. No person could by
conscious thought accomplish all these things. How, then, are they brought about?
Internal Laboratories. In the wonderful internal laboratory of the body there are little glands whose business it is to secrete chemicals for just these emergencies. When an object is sighted which arouses fear, the brain cells flash instantaneous messages over the body, among others to the supra-renal glands or adrenals, just over the kidneys, and to the thyroid gland in the neck. Instantly these glands pour forth adrenalin and thyroid secretion into the blood, and the body responds. Blood pressure rises; brain cells speed up; the liver pours forth glycogen, its ready-to-burn fuel; sweat-glands send forth cold perspiration in order to regulate temperature; blood is pumped out from stomach and intestines to the external muscles. As we have seen, the body as a whole can respond to just one stimulus at a time. The response to this stimulus has the right of way. The whole body is integrated, set for this one thing. When fear holds the switchboard no other messages are allowed on the line, and the creature is ready for flight.
But after flight comes concealment with the opposite bodily need, the need for absolute silence. This is why we sometimes get the opposite result. The heart seems to stop beating, the breath ceases, the limbs refuse to move, all because our ancestors needed to
hide after they had run, and because we are in a very real way a part of them.
Old-Fashioned Fear. There is one passage from Dr. Crile's book which so admirably sums up these points that it seems worth while to insert it at length.