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een hope and despair； it explains some of the phenomena of Graves' disease； of sexual neurasthenia； possibly of hay…fever and of the common cold。 The principle is probably equally applicable to the acute infections； in each of which chemical noci…association gives rise to many of the phenomena of the disease and it explains their cure by natural immunity and by vaccines。 This hypothesis should teach us to view our patients as a whole； and especially should it teach the surgeon gentleness。 It should teach us that there is something more in surgery than mechanics； and something more in medicine than physical diagnosis and drugs。
Conclusion
The brain…cells have existed for eons and； amid the vicissitudes of change； they have persisted with perhaps less alteration than has the crust of the earth。 Whether in man or in the lower animals； they are related to and obey the same general biologic laws； thus being bound to the entire past and performing their function in accordance with the law of phylogenetic association。
For so long a time have we directed our attention to tumors； infections； and injuries that we have not sufficiently considered the vital force itself。 We have viewed each anatomic and pathologic part as an entity and man as an isolated phenomenon in nature。 May we not find in the laws of adaptation under natural selection； and of phylogenetic association； the master key that will disclose to us the explanation of many pathologic phenomena as they have already explained many normal phenomena？
And may medicine not correlate the pathologic phenomena of the sick man with the forces of evolution； as the naturalists have correlated the phenomena of the sound man； and thus may not disease； as well as health； be given its evolutionary setting？
PHYLOGENETIC ASSOCIATION IN RELATION TO THE EMOTIONS＇*＇
＇*＇ Address before the American Philosophical Society； Philadelphia； April 22； 1911。
The surgeon is familiar with the manifestations of every variety of the human emotions in the various stations of life； from infancy to senility； in health and in disease。 Not only does he come into intimate contact with the emotions displayed by the victims of disease and of accidents； but he also observes those manifested by the relatives and friends of the families of his patients。 Moreover； he is unhappily forced to notice the emotional effect upon himself when he is waging an unequal battle against death the strain and worry at a crisis； when a life is in the balance and a single false move may be fatal； is an experience known only to the operating surgeon。
For the data for this paper； therefore； in which I shall for the most part limit my discussion to the strongest of all emotionsFEARI have drawn largely from my personal experience as a surgeon； as well as from an experimental research in which I have had the valuable assistance of my associates； Dr。 H。 G。 Sloan； Dr。 J。 B。 Austin； and Dr。 M。 L。 Menten。
I believe it can be shown that it is possible to elicit the emotion of fear only in those animals that utilize a motor mechanism in defense against danger or in escape from it。 For example； the defense of the skunk is a diabolic odor which repels its enemies； the skunk has no adequate equipment for defense or escape by muscular exertion； and the skunk therefore shows little or no fear。 Again； certain species of snakes are protected by venom； they possess no other means of defense nor have they adequate motor mechanisms for escape and they show no fear。 Because of their strength other animals； such as the lion； the grizzly bear； and the elephant； show but little fear （Fig。 6）。 Animals which have an armored protection； such as the turtle； show little fear。 It is； therefore； obvious that fear is not universal and that the emotion of fear is felt only by those animals whose self…preservation is dependent upon an uncertain adequacy of their power of muscular exertion either for defense or for flight （Fig。 7）。
What are the principal phenomena of fear？ They are palpitation of the heart； acceleration of the rate and alteration of the rhythm of the respiration； cold sweat； rise in body temperature； tremor； pallor； erection of the hair； suspension of the principal functions of digestion； muscular relaxation； and staring of the eyes （Fig。 12）。 The functions of the brain are wholly suspended except those which relate to the self…protective response against the feared object。 Neither the brain nor any other organ of the body can respond to any other lesser stimulus during the dominance of fear。
From these premises it would appear that under the influence of fear； most； perhaps all； of the organs of the body are divided sharply into two classes： First； those that are stimulated； and； second； those that are inhibited。 Those that are stimulated are the entire muscular system； the vasomotor and locomotor systems； the senses of perception； the respiration； the mechanism for erecting the hair； the sweat…glands； the thyroid gland； the adrenal gland （Cannon）； and the special senses。 On the other hand； all the digestive and procreative functions are inhibited。 What is the significance of this stimulation of some and inhibition of other organs？ As far as we know； the stimulated organs increase the efficiency of the animal for fight or for flight。 It is through skeletal muscles that the physical attack or escape is effected； these muscles alone energize the claws； the teeth； the hoofs； and the means for flight。 The increased action of the muscles of the heart and the blood…vessels increases the efficiency of the circulation； the secretion of the adrenal gland causes a rise in the blood…pressure； the increased action of the thyroid gland causes an increased metabolic activity； there is evidence that glycogen is actively called out； this being the most immediately available substance for the production of energy； the increased activity of the respiration is needed to supply the greater need of oxygen and the elimination of the increased amount of waste products； the dilatation of the nostrils affords a freer intake of air； the increased activity of the sweat…glands is needed to regulate the temperature of the body which the increased metabolism causes to rise。 The activity of all the organs of perceptionsight； hearing； smell is increased in order that the danger may be more accurately perceived。 It cannot be a mere coincidence that the organs and the tissues that are stimulated in the emotion of fear are precisely those that are actually utilized in a physical struggle for self…preservation。
Are any other organs stimulated by fear except those that can or that do assist in making a defensive struggle？ I know of none。 On the other hand； if an animal could dispense with his bulky digestive organs； whose functions are suspended by fear； if he could； so to speak； clear his decks for battle； it would be to his advantage。 Although the marvelous versatility of natural selection apparently could devise no means of affording this advantage； it nevertheless shut off the nervous current and saved the vital force which is ordinarily consumed by these non…combatants in the performance of their functions。 Whatever may be the origin of fear； its phenomena are due to a stimulation of all the organs and tissues that add to the efficiency of the physical struggle for self…preservation and an inhibition of the func…
｛illust。 caption = FIG。 19THE BROAD JUMP。 Note the similarity of the expression to the facial expression of fear and of anger （Figs。 12 and 21）。 （Wm。 J。 Brownlow； drawn from photo。） tions of the leading organs that do not participate in that struggle the non…combatants； so to speak。 Fear arose from injury； and is one of the oldest and surely the strongest emotion。 By the slow process of vast empiricism nature has evolved the wonderful defensive motor me…chanism of many animals and of man。 The stimulation of this mechanism leading to a physical struggle is action； and the stimulation of this mechanism without action is emotion。 We may say； therefore； that fear is a PHYLOGENETIC FIGHT OR FLIGHT （Fig。 18）。 On this hypothesis all the organs and parts ｛illust。 caption = FIG。 20。…FINISH OF RELAY RACE。
Compare the facial expression of the runners with those in Figs。 12； 19； 22。 These pictures illustrate the fact that the same mechanism is stimulated in emotion as in physical action。 （Photo by Underwood and Underwood； N。 Y。）｝
of the body are integrated； connected； or correlated for the self…preservation of the individual by the activity of his motor mechanism （Figs。 12； 19； and 20）。 We fear not in our hearts alone； not in our brains alone； not in our viscera alonefear influences every organ and tissue； each organ or tissue is stimulated or inhibited according to its use or hindrance in the physical struggle for existence。 By thus concentrating all or most of the nerve force on the nerve…muscular mechanism for defense； a greater physical power is developed。 Hence it is that under the stimulus of fear animals are able to perform preternatural feats of strength。 For the same reason； the exhaustion following fear will be increased as the powerful stimulus of fear drains the cup of nervous energy even though no visible act