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fear itself is an injury which when recognized is instinctively avoided。 In a similar manner anger may be softened or banished by an appeal to the stronger self…preserving instinct aroused by the fear of physical damage； such as the physical injury of brain…cells。 This playing of one primitive instinct against another is comparable to the effect produced upon two men who are quarreling when a more powerful enemy of both comes threateningly on the scene。
The acute fear of a surgical operation may be banished by the use of certain drugs that depress the associational power of the brain and so minimize the effect of the preparations that usually inspire fear。 If； in addition； the entire field of operation is blocked by local anesthesia so that the associational centers are not awakened； the patient will pass through the operation unscathed。
The phylogenetic origin of fear is injury； hence injury and fear cause the same phenomena。 In their quality and in their phenomena psychic shock and traumatic shock are the same。 The perception of danger by the special senses in the sound of the opening gun of a battle； or in the sight of a venomous snake； is phylogenetically the same and causes the same effects upon the entire body as an operation under anesthesia or a physical combat in that each drives the motor mechanism。 The use of local anesthetics in the operative field prevents nerve…currents from the seat of injury from reaching the brain and there integrating the entire body for a self…defensive struggle。 The result； even though a part of the brain is asleep and the muscles paralyzed； is the same as that produced by the interception of the terrifying sound of the gun； or of the sight of the dangerous reptile； since the stimulation of the motor mechanism is prevented。
By both the positive and the negative evidence we are forced to believe that the emotions are primitive instinctive reactions which represent ancestral acts； and that they therefore utilize the complicated motor mechanism which has been developed by the forces of evolution as that best adapted to fit the individual for his struggle with his environment or for procreation。
The mechanism by which the motor acts are performed and the mechanism by which the emotions are expressed are one and the same。 These acts in their infinite complexity are suggested by association phylogenetic association。 When our progenitors came in contact with any exciting element in their environment； action ensued then and there。 There was much actionlittle restraint or emotion。 Civilized man is really in auto…captivity。 He is subjected to innumerable stimulations； but custom and convention frequently prevent physical action。 When these stimulations are sufficiently strong but no action ensues； the reaction constitutes an emotion。 A phylogenetic fight is anger； a phylogenetic flight is fear； a phylogenetic copulation is sexual love； and so one finds in this conception an underlying principle which may be the key to an understanding of the emotions and of certain diseases。
PAIN； LAUGHTER； AND CRYING＇*＇
＇*＇ Address delivered before the John Ashhurst； Jr。。 Surgical Society of the University of Pennsylvania； May 3； 1912。
PAIN
Pain； like other phenomena； was probably evolved for a particular purpose surely for the good of the individual； like fear and worry； it frequently is injurious。 What then may be its purpose？
We postulate that pain is one of the phenomena which result from a stimulation to motor action。 When a barefoot boy steps on a sharp stone it is important that the injuring contact be released as quickly as possible； and therefore physical injury pain results and impels the required action。 Anemia of the soft parts at the points of pressure results from prolonged sitting or lying in one position； and as a result pain compels a muscular action that shifts the damaging pressurethis is the pain of anemia； when the rays of the blazing sun shine directly upon the retina； pain immediately causes a protective muscular actionthe lid is closed； the head turns awaythis is light pain； when standing too close to a blazing fire the excessive heat causes a pain which results in the protective muscular action of moving awaythis is heat pain； when the urinary bladder is acutely overdistended the resultant pain induces voluntary as well as involuntary muscular contraction this is evacuation pain； associated with defecation is a characteristic warning pain； and an active pain which induces the required muscular actionthis； like the pain accompanying micturition； is an evacuation pain； in obstruction of the urinary passages and of the large and the small intestine the pain is exaggerated； as is the accompanying muscular contractionthis is a pathologic evacuation pain； when the fetus reaches full term and labor is to begin； it is heralded by pain which is associated with rhythmic contractions of the uterine muscle； later； many other muscles take part in the birth and pain is associated with all these muscular contractionsthese are labor pains； when a foreign body； be it ever so small； falls upon the conjunctiva or cornea there results what is perhaps the acutest pain known； and quick and active muscular action followsthis is special contact pain。 Special pain receptors are placed in certain parts of the nose； the pharynx； and the larynx； the stimulation of which causes special motor acts； such as sneezing； hawking； coughing。 Curiously vague pains are associated with the protective motor act of vomiting and with the sexual motor actsthese may be termed nausea pains and pleasure pains。 We now see； therefore； that against the injurious physical contacts of environment； against heat and cold； against damaging sunlight； against local anemia when resting or sleeping； the body is protected by virtue of the muscular action which results from pain。 Then； too； for the emptying of the pregnant uterus； for the evacuation of the intestine and of the urinary bladder as normal acts； and for the overcoming of obstructions in these tracts； pain compels the required muscular actions； For passing gall…stones and urinary calculi； urgent motor stimuli are awakened by pain。 For each of these diversified pains the consequent muscular action is specific in type； distribution； and intensity。 This statement is so commonplace that we are apt to miss the significance and the wonder of it。 It is probable that every nerve…ending in the skin and every type of stimulation represents a separate motor pattern； the adequate stimulation of which causes always the same response。
Let us pass on to the discussion of another and perhaps even more interesting type of pain； that associated with infection。 Not all kinds of infection are painful； and in those infections that may be associated with pain there is pain only when certain regions of the body are involved。 Among the infections that are not associated with pain are scarlet fever； typhoid fever； measles； malaria； whooping…cough； typhus fever； and syphilis in its early stages。 The infections that are usually； though not always； associated with pain are the pyogenic infections。 The pyogenic infections and the exanthemata constitute the great majority