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sponse and occurs only as a result of contact ceptor stimulation by physical injury； infection； anemia； or obstruction； we may well inquire which part of the nerve mechanism is the site of the phenomenon of pain。 Is it the nerve…ending； the nerve…trunk； or the brain？ That is； is pain associated with the physical contact with the nerve…ending； or with the physical act of transmission along the nerve…trunk； or with the change of brain…cell substance by means of which the motor…producing energy is released？
We postulate that the pain is associated with the discharge of energy from the brain…cells。 If this be true； then if every nociceptor in the body were equally stimulated in such a manner that all the stimuli should reach the brain…cells simultaneously； then the cells would find themselves in equilibrium and no motor act would be performed。 But if all the pain nerve ceptors but one were equally stimulated； and this one more strongly stimulated than the rest； then this one would gain possession of the final common pathwould cause a muscular action and the sensation of pain。
It is well known that when a greater pain or stimulus is thrown into competition with a lesser one； the lesser is submerged。 Of this fact the school…boy makes use when he initiates the novice into the mystery of the painless pulling of hair。 The simultaneous but severe application of the boot to the blindfolded victim takes complete but exclusive possession of the final common path and the hair is painlessly plucked as a result of the triumph of the boot stimulus over the pull on the hair in the struggle for the final common path。
Persons who have survived a sudden； complete exposure to superheated steam； or whose bodies have been enwrapped in flame； testify that they have felt no pain。 As this absence of pain may be due to the fact that the emotion of fear gained the final common path； to the exclusion of all other stimuli； we are trying by experimentation to discover the effects of simultaneous painful stimulation of all parts of the body。 The data already in hand； and the experiments now in progress； in which anesthetized animals are subjected to powerful stimuli applied to certain parts of the body only； or simultaneously to all parts of the body； lead us to believe that in the former case the brain…cells become stimulated or hyperchromatic； while in the latter case no brain…cell changes occur。 We believe that our experiments will prove that an equal and simultaneous stimulation of all parts of the body leaves the brain…cells in a state of equilibrium。 Our theory of pain will then be well sustained； not only by common observation； but by experimental proof； and so the mechanistic view will be found in complete harmony with another important reaction。
We have stated that when a number of contact stimuli act simultaneously； the strongest stimulus will gain possession of the final common path the path of action。 When； however； stimuli of the distance ceptors compete with stimuli of the contact ceptors； the contact…ceptor stimuli often secure the common path； not because they are stronger or more important； but because they are immediate and urgent。 In many instances； however； the distance…ceptor stimuli are strong； have the advantage of a lowered threshold； and therefore compete successfully with the immediate and present stimuli of the contact ceptors。 In such cases we have the interesting phenomenon of physical injury without resultant pain or muscular response。 The distance…ceptor stimuli which may thus triumph over even powerful contact…ceptor stimuli are those causing strong emotionsas great anger in fighting； great fear in a battle； intense sexual excitement。 Dr。 Livingstone has testified to his complete unconsciousness to pain during his struggle with a lion； although he was torn by teeth and claws； his fear overcame all other impressions。 By frequently repeated stimulation the Dervish secures a low threshold to the emotions caused by the thought of God or the devil； and his emotional excitement is increased by the presence of others under the same stimulation； emotion； therefore； secures the final common path and he is unconscious of pain when he lashes； cuts； and bruises his body。 The phenomena of hysteria may be explained on this basis； as may the unconsciousness of passing events in a person in the midst of a great and overwhelming grief。 By constant practice the student may secure the final common path for such impressions as are derived from the stimuli offered by the subject of his study； and so he will be oblivious of his surroundings。 Concentration is but another name for a final common path secured by the repetition and summation of certain stimuli。
If our premises are sustained； then we can recognize in man no will； no ego； no possibility for spontaneous action； for every action must be a response to the stimuli of contact or distance ceptors； or to their recall through associative memory。 Memory is awakened by symbols which represent any of the objects or forces associated with the act recalled。 Spoken and written words； pictures； sounds； may stimulate the brain patterns formed by previous stimulation of the distance ceptors； while touch； pain； temperature； pressure； may recall previous contact…ceptor stimuli。 Memory depends in part upon the adequacy of the symbol； and in part upon the state of the threshold。 If one has ever been attacked by a snake； the threshold to any symbol which could recall that attack would be low； the later recall of anything associated with the bite or its results would produce in memory a recapitulation of the whole scene； while even harmless snakes would thereafter be greeted with a shudder。 On the other hand； in a child the threshold is low to the desire for the possession of any new and strange object； in a child； therefore； to whom a snake is merely an unusual and fascinating object； there is aroused only curiosity and the desire for the possession of a new plaything。
If we are to attribute to man the possession of a governing attribute not possessed by other parts of the animal creation； where are we to draw the boundary line； and say 〃here the ego the willthe reasonemerges〃？ What attribute； after all； has man which in its ultimate analysis is not possessed by the lowest animals or by the vegetable creation； even？ From the ameba； on through all the stages of animal existence； every action is but a response to an adequate stimulus； and as a result of adequate stimuli each step has been taken toward the higher and more intricate mechanisms which play the higher and more intricate parts in the great scheme of nature。
The Venus fly…trap responds to as delicate a stimulus as do any of the contact ceptors of animals； and the motor activity resulting from the stimulus is as complex。 To an insect…like touch the plant responds； to a rough contact there is no response； that is； the motor mechanism of the plant has become attuned to only such stimuli as simulate the contact of those insects which form its diet。 It catches flies； eats and digests them； and ejects the refuse （Fig。 47）。 The ameba does no less。 The frog does no more； excepting that in its place in creation a few more reactions are required for its sustenance and for the propagation of its species。 Man does no more； excepting that in man's manifold relations there are innumerable stimuli； for meeting which adequately； innumerable mechanisms have been evolved。 The motor mechanism of the fly…trap is perfectly adapted to its purpose。 The motor mechanism of man is adapted to its manifold uses； and as new environmental influences surround him； we must believe that new adaptations of the mechanism will be evolved to meet the new conditions。
Is not this conception of man's activities infinitely more wonderful； and infinitely more comprehensible than is the conception that his activities may be accounted for by the existence of an unknown； unimaginable； and intangible force called 〃mind〃 or 〃soul〃？
We have already shown how the nerve mechanism is so well adapted to the innumerable stimuli of environment that it can accurately transmit and distinguish between the infinite variations of speed in the ether waves producing light； and the air waves producing sound。 Each rate of vibration energizes only the mechanism which has been attuned to it。 With marvelous accuracy the light and sound waves gain access to the nerve tissue and are finally interpreted in terms of motor responses； each by the brain pattern attuned to that particular speed and intensity。 So stimuli and resultant actions multiplied by the total number of the motor patterns in the brain of man give us the sum total of his life's activities they constitute his life。
As in evolutionary history the permanence of an adaptation of the body mechanism depends upon its value in the preservation of the life of the individual and upon its power to increase the value of the individual to the race； so the importance and truth of these postulates and theories may well be judged on the same basis。
The fundamental instincts of all living matter are self…preservation and the propagation of the species。 The instinct for self…preservation causes a plant to turn away from cold and damagin