The fear instinct in its course of development passes through three stages:
I.    The Stimulating Stage
II.    The Arrestive, or Inhibitory Stage
III.    The Paralyzing Stage.

In its milder forms when the fear instinct is but nascent, it serves as a sort of trigger to the activities of the organism. The animal may for a moment stop whatever activities and pursuits in which it happens to be engaged, and have its interest turn in the direction of the particular new stimulus, whether it be of an auditory, visual, or olfactory character. The fear instinct is just strong enough to suspend present interests, and direct its activities to the new source of the unknown stimulus.

When the source is unfamiliar, the animal becomes prepared for action. The energies are aroused for attack, or for hiding, freezing, or running, according to the mode of defense to which the animal has[28] been adapted in its adjustments to the stimulations of its environment. The lion, the tiger, the skunk, the snake, the bird, the rabbit, the squirrel will act differently, according to their natural disposition in response to external objects and stimuli.

While the motor system may react differently in various animals, the fear instinct is alike in all of them. This stage of the fear instinct should be regarded as the healthy physiological reaction to strange and new stimuli, and is essentially protective, inasmuch as it serves for the arousal of energy and proper reactions of self-defense, characteristic of the particular individual.

In its milder forms the fear instinct is normal, physiological, and healthy in its reactions. In fact, the absence of it is rather pathological. It is quite natural that under the influence of some danger, the organism may feel the urging of this vital instinct, the consequent of the fundamental life impulse, and feel it as a stimulus rather than as a deterrent experience, feel fear as the key for the unlocking of energies in defense or attack. Such a reaction is healthy and strictly requisite in the total economy of life.

When I advanced the theory that the fear instinct is at the bottom of functional psychosis, or of psychopathic maladies, some jumped to the conclusion that I regarded the fear instinct as abnormal, giving rise to pathological states under all[29] conditions and circumstances. This is not correct. The fear instinct in its initial stages is perfectly normal, and is as indispensable to life as hunger and thirst. It is only in the more advanced and extreme stages that the fear instinct becomes pathological, and is apt to give rise to psychopathic states.

In the arrestive or inhibitory state, the innervation of the voluntary and the involuntary muscular systems is arrested, or weakened. There is tremor and even convulsive contractions, the voluntary reactions are affected, and are carried out with some difficulty; there is cardiac arrhythmia, the respiration is irregular; there may be chattering of the teeth; the various bodily secretions are interfered with, and the vaso-motor nerves as well as the general vascular structures are thrown into disorder. Peristalsis, intestinal secretions, and the innervation of the sympathetic nervous system may become affected, first by inhibition, and then by irregular functioning. Associative mental or cerebral activity becomes arrested, confused; memory is disturbed, and the whole personality or individuality appears in a state of dissociation, accompanied by a lack of precision and lack of exactness of neuromuscular adaptations. The delicate reactions and adaptations are specially affected.

If this stage of fear instinct does not become intensified, the organism recovers its control,—many[30] of the disturbances pass away, and the following reaction may come with a greater release of energy, developing a greater output of activity than under normal conditions. In short, the fear instinct may still serve as a stimulation to greater effort, but the chances of such a result are far smaller than in the first stage, which is essentially of a stimulating, useful, and healthful character.

The second stage of the fear instinct is the possibility of a pathological state, and, if persistent, leads directly to the third stage with consequent paralysis and danger of destruction. The first stage of fear is fully normal, helpful, and self-defensive. The second stage is harmful, but with the possibility of recovery and restitution of normal function. The third stage leads to destruction and death.

In the third stage there is paralysis of function of most of the muscular, secretory, excretory, circulatory, intestinal, and nervous systems. The animal is petrified with fear, and falls into a state of paralysis, rigidity, cataplexy, or in a state simulating death. This last stage of the effects of the fear instinct is pathological, and instead of conducing to the good of the individual, really leads to his destruction and death. The fear instinct in its extreme cases is not a help to the organism, but is distinctly a hindrance, and is felt as such by the organism which experiences it.

The fear instinct, which originally is a stimulating[31] agent for self-defense, when in excess becomes a danger hastening the dissolution of the animal organism into its constituent parts. The intensity of the fear instinct is the expression of the fact that the organism is in imminent danger of destruction. The fear instinct in its extreme state is decidedly to the disadvantage of the animal.

Of course, it may be claimed that the paralysis and inhibition stages might have been of service or of protective value in the lower forms of life, when mimicking death or freezing prevented the animal from being noticed. This may possibly hold true in the cases of lower forms, but in the higher forms the fear instinct in its third stage, by bringing about inhibitions and paralysis of the vital functions, is decidedly of disservice to the organism, and leads to its destruction and death.