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licable manner in which perspiration immediately exudes from it。 This exudation is all the more remarkable as the surface is then cold； and hence the term； ‘a cold sweat'； whereas the sudorific glands are properly excited into action when the surface is heated。 The hairs also on the skin stand erect； and the superficial muscles shiver。 In connection with the disturbed action of the heart； the breathing is hurried。 The salivary glands act imperfectly； the mouth becomes dry； and is often opened and shut。 I have also noticed that under slight fear there is a strong tendency to yawn。 One of the best…marked symptoms is the trembling of all the muscles of the body； and this is often first seen in the lips。 From this cause； and from the dryness of the mouth； the voice becomes husky and indistinct； or may altogether fail。 * * * As fear increases into agony of terror； we behold； as under all violent emotions； diversified results。 The heart beats wildly； or may fail to act and faintness ensues； there is death…like pallor； the breathing is labored； the wings of the nostrils are widely dilated； ‘there is a gasping and convulsive motion of the lips； a tremor on the hollow cheek； a gulping and catching of the throat'； the uncovered and protruding eyeballs are fixed on the object of terror； or they may roll restlessly from side to side。 * * * The pupils are said to be enormously dilated。 All the muscles of the body may become rigid； or may be thrown into convulsive movements。 The hands are alternately clenched and opened； often with a twitching movement。 The arms may be protruded； as if to avert some dreadful danger； or may be thrown wildly over the head。 * * * In other cases there is a sudden and uncontrollable tendency to headlong flight； and so strong is this that the boldest soldiers may be seized with a sudden panic。 As fear rises to an extreme pitch； the dreadful scream of terror is heard。 Great beads of sweat stand on the skin。 All the muscles of the body are relaxed。 Utter prostration soon follows； and the mental powers fail。 The intestines are affected。 The sphincter muscles cease to act and no longer retain the contents of the body。 * * * Men； during numberless generations； have endeavored to escape from their enemies or danger by headlong flight； or by violently struggling with them； and such great exertions will have caused the heart to beat rapidly； the breathing to be hurried； the chest to heave； and the nostrils to be dilated。 As these exertions have often been prolonged to the last extremity； the final result will have been utter prostration； pallor； perspiration； trembling of all the muscles； or their complete relaxation。 And now； whenever the emotion of fear is strongly felt； though it may not lead to any exertion； the same results tend to reappear； through the force of inheritance and association〃＇*＇ （Fig。 12）。
＇*＇ Darwin： Expression of the Emotions in Man and Animals。
In an experimental research； we found evidence that the physiologic phenomena of fear have a physical basis。 This evidence is found in the morphologic alterations in the brain…cells； which are similar to those observed in certain stages of surgical shock and in fatigue from muscular exertion （Figs。 2； 4； 5； and 13）。 For the present； we shall assume that fear is a REPRESENTATION of trauma。 Because fear was created by trauma； fear causes a discharge of the energy of the nervous system by the law of phylogenetic association。 The almost universal fear of snakes； of blood； and of death and dead bodies may have such a phylogenetic origin。 It was previously stated that under the stimulus of fear animals show preternatural strength。 An analysis of the phenomena of fear shows that； as far as can be determined； all the functions of the body requiring the expenditure of energy； and which are of no direct assistance in the effort toward self…preservation； are suspended。 In the voluntary expenditure of muscular energy； as in the chase； the suspension of other functions is by no means so complete。 Fear and trauma may drain to the last dreg the dischargeable nervous energy； and； therefore； the greatest possible exhaustion may be produced by fear and trauma。
Summation
In the discharge of energy； summation plays an important role。 Summation is attained by the repetition of stimuli at such a rate that each succeeding stimulus is applied before the nerve…cells have returned to the resting stage from the preceding stimulus。 If drops of water fall upon the skin from a sufficient height to cause the slightest unpleasant sensation； and at such a rate that before the effect of the stimulus of one drop has passed another drop falls in precisely the same spot； there will be felt a gradually increasing painful sensation which finally becomes unbearable。 This is summation of stimuli。 When； for a long time； a patient requires frequent painful wound dressings； there is a gradual increase in the acuteness of the pain of the receptors。 This is caused by summation。 In a larger sense； the entire behavior of the individual gives considerable evidence of summation； _e。 g_。； in the training of athletes； the rhythmic discharge of muscular energy at such intervals that the resting stage is not reached before a new exercise is given results in a gradual ascent in efficiency until the maximum is reached。 This is summation； and summation plays a large role in the development of both normal and pathologic phenomena。
We have now pointed out the manner in which at least a part of the nervous energy of man may be discharged。 The integrative action of the nervous system and the discharge of nervous energy by phylogenetic association may be illustrated by their analogy to the action of an electric automobile。 The electric automobile is composed of four principal parts： The motor and the wheels （the muscular system and the skeleton）； the cells of the battery containing stored electricity （brain…cells； nervous energy）； the controller； which is connected with the cells by wiring （the receptors and the nerve…fibers）； and an accelerator for increasing the electric discharge （thyroid gland？）。 The machine is so constructed that it acts as a whole for the accomplishment of a single purpose。 When the controller is adjusted for going ahead （adequate stimulus of a receptor）； then the conducting paths （the final common path） for the accomplishment of that purpose are all open to the flow of the current from the battery； and the vehicle is integrated to go ahead。 It spends its energy to that end and is closed to all other impulses。 When the controller is set for reverse； by this adequate stimulus the machine is integrated to back； and the battery is closed to all other impulses。 Whether integrated for going forward or backward； if the battery be discharged at a proper rate until exhausted； the cells； though possessing no more power （fatigue）； have sustained no further impairment of their elements than that of normal wear and tear。 Furthermore； they may be restored to normal activity by recharging （rest）。 If the vehicle be placed against a stone wall； and the controller be placed at high…speed （trauma and fear）； and if the accelerator be used as well （thyroid secretion？）； though the