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ch as the exanthemata； typhoid fever； and auto…intoxication； which have no dominating local disturbances to act as policemen to put the individual to bed and to make him refuse food that he may be in the most favorable position to combat the oncoming disease； in such cases in which these masterful and beneficent local influences are absent we postulate that headache has been evolved to perform this important service。
On the hypothesis that it is good for the individual who is acutely stricken by a disease or who is poisoned by autointoxication to rest and fast； and that the muscular system obeys the imperial command of pain； and in view of the fact that the brain is not only in constant touch with the conditions of every part of the body but that it is also the controlling organ of the body； one would expect that in these diseases the major pain whose purpose it is to govern general muscular action would be located in the head and there we find it。 How curious and yet how intelligible is the fact that； though a headache may be induced by even a slight auto…intoxication； an abscess may exist within the brain without causing pain。 When an obliterative endarteritis is threatening a leg with anemic gangrene； or when one lies too long in the same position on a hard bed； there is threatening injury from local anemia； and as a result there is acute pain； but when the obliterative endarteritis threatens anemia of the brain； or when an embolism or thrombosis has produced anemia of the brain； there may be no accompanying pain。 The probable explanation of the pain which results in the first instance and the lack of pain in the second is that in the former muscular action constitutes a self…protective response； but in the other it does not。 Diseases and injuries of the brain are notoriously difficult to diagnosticate。 This may well be because it has always been so well protected by the skull that there have been evolved within it few tell…tale self…protective responses； so that in the presence of injury and disease within itself the brain remains remarkably silent。 It should occasion no surprise that there are in the brain no receptors； the mechanical stimulation of which can cause pain； because its bony covering has always prevented the adaptive implantation within it of contact pain receptors。 Dr。 Frazier tells me that in the course of his operations on the brains of unanesthetized patients he is able to explore the entire brain freely and without pain。 From my own experience I am able to confirm Dr。 Frazier's observation。 In addition； the two…stage operation for the excision of the Gasserian ganglion provides an observation of extraordinary interest。 If at the first seance the ganglion is exposed； but is not disturbed except by the iodoform gauze packing； then on the following day the gauze may be removed； the ganglion picked up； and its branches and root excised without anesthesia and without pain。 The same statement and explanation may be made regarding the distribution of pain receptors for physical contact within the parenchyma of the liver； the gall…bladder； the abdominal viscera； the spleen； the heart； the lungs； the retroperitoneal tissue； the deep tissue of the back； the vertebrae； and in certain portions of the spinal cord。 Just what is the distribution of the receptors for heat and for cold I am unable to state； but this much we do know； that without anesthesia the intestines may be cauterized freely without the least pain resulting； and in animals the cauterization of the brain causes no demonstrable change in the circulatory or respiratory reactions。 It is probable therefore that the distribution of the pain receptors for physical contact and for heat are limited to those parts of the body that have been exposed to injurious contacts with environment。
Of special significance is the pain which is due to cold； which increases muscular tone and produces shivering。 The general increase in muscular tone produces an interesting postural phenomenon： the limbs are flexed and the body bent forward； a position which probably is due to the fact that the flexors are stronger than the extensors。 As muscular action is always accompanied by heat production； the purpose of the muscular contraction and the shivering is quite certainly caused by cold to assist in the maintenance of the normal body temperature。
We have now discussed many of the causes of pain and in each instance we have found an associated muscular action which apparently serves some adaptive purpose （Figs。 24 and 25）。 If we assume that pain exists for the purpose of stimulating muscular reactions； we may well inquire what part of the nervous are is the site of the sensation of painthe nerve…endings； the trunk； or the brain？ Does pain result from physical contact with the nerve…endings； with the physical act of transmitting an impression along the nerve trunk； or with the process within the brain…cells by which energy is released to cause a motor act？
It seems most probable that the site of the pain is in the brain…cells。 If this be so； then what is the physical process by which the phenomena of pain are produced？ The one hypothesis that can be tested experimentally is that pain is a phenomenon resulting from the rapid discharge of energy in the brain…cells。 If this be true； then if every pain receptor of the body were equally stimulated in such a manner that
｛illust。 caption = FIG。 25。FEAR AND AGONY。 〃Amid this dread exuberance of woe ran naked spirits wing'd with horrid fear。〃 Dante's 〃Inferno；〃 Canto XXIV； lines 89； 90。 all the stimuli reached the brain…cells simultaneously； the cells would find themselves in equilibrium and no motor act would be performed。 But if all the pain receptors of the body but one were equally stimulated； and this one stimu…lated harder than the rest； then the latter would gain possession of the final common path； the sensation of pain would be felt； and a muscular contraction would result。 It is well known that when a greater pain is thrown into competition with a lesser one； the lesser is completely submerged。 In this manner the school…boy initiates the novice into the mystery of the painless plucking of hair。 The simultaneous； but severe application of the boot to the blindfolded victim takes complete and exclusive possession of the final common path and the hair is painlessly plucked through the triumph of the boot stimulus over the hair stimulus in the struggle for the possession of the final common path。 Another argument in favor of this hypothesis that pain is an accompaniment of the release of energy in the brain… cells is found in the fact that painless stimuli received through the special senses may completely submerge the painful stimuli of physical injury； for although the stimuli to motor action； which are received through the senses of sight； hearing； and smell； cause even more powerful motor action than those caused by physical contact stimuli； yet they are not accompanied by pain。 Examples of this triumph of stimulation of the special senses over contact stimulation are frequently seen in persons obsessed by anger or fear； and to a less degree in those obsessed by sexual emotion。 In the fury of battle the soldier may not perceive his wound until the emotional excitation is wearing away； when the sensation of warm blood on the skin may first attract his attention。 Religious fanatics are said to feel no pain when they subject themselves to self…injury。 Now； since both psychic and mechanical stimuli cause motor action by the excitation ofprecisely the same mechanism in the brain； and since the more rapid release of energy from psychic stimuli submerges the physical stimuli and prevents pain； it would seem that pain must be a phenomenon which is associated with the process of releasing energy by the brain…cells。 Were physical injury inflicted in a quiescent state equal to that inflicted in the emotional state； great pain and intense muscular action would be experienced。 Now the emotions are as purely motor excitants as is pain。 The dynamic result is the same the principal difference being the greater suddenness and the absolute specificity of the pain stimuli as compared with the more complex and less peremptory stimuli of the emotions。 A further evidence that pain is a product of the release of brain…cell energy is the probability that if one could pierce the skin at many points on a limb in such a manner that antagonistic points only were equally and simultaneously stimulated； then an equilibrium in the governing brain… cells would be established and neither pain nor motion would follow。 An absolute test of this assumption cannot be made but it is supported by the obtainable evidence。 We will now turn to a new viewpoint； a practical as well as a fascinating one； which can best be illustrated by two case histories： A man； seventy…eight years old； whose chief complaint was obstinate constipation； was admitted to the medical ward of the Lakeside Hospital several years ago。 The abdomen was but slightly distended； there was no fever； no increased leukocytosis； no muscular rigidity； and but slight general tenderness。 He claimed to have lost in weight and strength during the several months previous to his admission。 A tent