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imed to have lost in weight and strength during the several months previous to his admission。 A tentative diagnosis of malignant tumor of the large intestine was made； but free movements weresecured rather easily； and we abandoned the idea of an exploratory operation。 The patient gradually failed and died without a definite diagnosis having been made by either the medical or the surgical service。 At autopsy there was found a wide…spread peritonitis arising from a perforated appendix。 A child； several years old； was taken ill with some indefinite disease。 A number of the ablest medical and surgical consultants of a leading medical center thoroughly and repeatedly investigated the case。 Although they could make no definite diagnosis they all agreed that the trouble surely could not be appendicitis because there was neither muscular rigidity nor tenderness。 The autopsy showed a gangrenous appendix and general peritonitis。 How can these apparently anomalous cases be explained？ These two cases are illustrations of the same principle that underlies the freedom from pain which results from the use of narcotics and anesthetics； the same principle that explains the fact that cholecystitis may occur in the aged without any other local symptoms than the presence of a mass and perhaps very slight tenderness； and that accounts in general for the lack of well…expressed disease phenomena in senility and in infancy。 The reason why the aged； the very young； and the subjects of general paresis show but few symptoms of disease is that in senility the brain is deteriorated； while in infancy the brain is so undeveloped that the mechanism of association is inactive； hence pain and tenderness； which are among the oldest of the associations； are wanting。 Senility and infancy are by nature normally narcotized。 The senile are passing through the twilight into the night； while infants are traversing through the dawn into the day。 Hence it is that the diagnosis of injury and disease in the extremes oflife is beset by especial difficulties； since the entire body is as silent as are the brain； the pericardium； the mediastinum； and other symptomless areas。 For the same reason； when a patient who is seriously ill with a painful disease turns upon the physician a glowing eye and an eager face； and remarks how comfortable he feels； then the end is near。 This is a brilliant and fateful clinical mirage。 When one reflects on the vast amount of evidence as to the origin and the purpose of pain； he is forced to conclude that pain is a phenomenon of motor stimulation； and that its principal role is the protection of the individual against the gross and the microscopic enemies in his environment。 The benefits of pain are especially manifested in the urgent muscular actions by means of which the body moves away from physical injury； obstructions of the hollow viscera are overcome； rest is compelled in the acute infections the infected points are held rigidly quiet； the muscles of the abdomen are fixed； and harmful peristalsis is arrested in peritonitis； while there is absolutely no pain in the diseases or injuries which affect those regions of the body in which in the course of evolution no pain receptors were placed； or in those diseases in which muscular inhibition or contraction is of no help。 In a biologic sense pain is closely associated with the emotional stimuli； for both pain and the emotions incite motor activity for the good of the individual。 The frequent occurrence of post…operative and post… traumatic pain is accounted for by the fact that the operation or the injury has lowered the threshold of the brain… cells to trauma； the brain and not the local sensitive field is the site of the pain。 I have found that； by blockingthe field of operation with local anesthesia； post…operative pain is diminished； that is； since the local anesthesia prevents the strong stimuli of the trauma from reaching the brain； its threshold is not lowered。 There is a close resemblance between the phenomena of pain habit； of education； of physical training； of love and of hate。 In education； in pain habit； in all emotional relations； a low brain… cell threshold is established which facilitates the reception of specific stimuli； all these processes are motor acts； or are symbolic of motor acts； and we may be trained to perceive misfortune and pain as readily as we are trained to perceive mathematical formulae or moral precepts。 In each and every case； readiness of perception depends； as it seems to me； upon a modified state of the brain…cells； their threshold especially； the final degree of perception possible in any individual being perhaps based on the type of potential molecules of which the brain is built。 We must believe also that every impression is permanent； as only thus could an individual animal or a man be fitted by his own experience for life's battles。 LAUGHTER AND CRYING What is laughter？ What is its probable origin； its distribution； and its purpose？ Laughter is an involuntary rhythmic contraction of certain respiratory muscles； usually accompanied by certain vocal sounds。 It is a motor act of the respiratory apparatus primarily； although if intense it may involve not only the extraordinary muscles of respiration； but most of the muscles of the body。 There are many degrees of laughter； from the mere brightening of the eyes； a fleeting smile； tittering andgiggling； to hysteric and convulsive laughter。 Under certain circumstances； laughter may be so intense and so long continued that it leads to considerable exhaustion。 The formation of tears is sometimes associated with laughter。 When integrated with laughter； the nervous system can perform no other function。 Crying is closely associated with laughter； and in children especially laughter and crying are readily interchanged。 We postulate that laughter and weeping serve a useful purpose。 According to Darwin； only man and monkeys laugh （Fig。 26）； other animals exhibit certain types of facial expression accompanying various emotions； but laughter in the sense in which that word is commonly used is probably an attribute of the primates only； although it is probable that many animals find substitutes for laughter。 The proneness of man to laughter is modified by age； sex； training； mental state； health； and by many other factors。 Healthy； happy children are especially prone to laughter； while disease； strong emotions； fatigue； and age diminish laughter。 Women laugh more than do men。 The healthy； happy maturing young woman perhaps laughs most； especially when she is slightly embarrassed。 What causes laughter？ Good news； high spirits； tickling； hearing and seeing others laugh； droll stories； flashes of wit； passages of humor； averted injury； threatened breach of the conventions； and numerous other causes might be added。 It is obvious that laughter may be produced by diverse influences； many of which are so unlike each other that it would at first sight seem improbable that a single general principle underlies all。 Before presenting a hypothesis which harmonizes most of the facts； and which mayoffer an explanation of the origin and purpose of laughter； let us return for a moment to some previous considerations that man is essentially a motor being； that all his responses to the physical forces of his environment are motor； ｛illust。 caption = FIG。 26。LAUGHING CHIMPANZEE。 〃Mike；〃 the clever chimpanzee in the London Zoo； evidently enjoys a joke as well as any one else。 （Photo by Underwood and Underwood； N。 Y。）｝
that thoughts and words even are symbolic of motor acts； that in the emotions of fear； of anger； and of sexual love the whole body is integrated for acts which are not performed。 These integrations stimulate the brain…cells； the ductless glands； and other parts； and the energizing secretions； among which are epinephrin； thyroid and hypophyseal secretions； are thrown into the blood…stream； while that most available fuel； glycogen； is also mobilized in the blood。 This body…wide preparation for action may be designated kinetic reaction。 The fact that emotion is more injurious to the body than is muscular action is well known； the difference being probably caused by the fact that when there is action the above…mentioned products of stimulation are consumed； while in stimulation without action they are not consumed and must be eliminated as waste products。 Now these activating substances and the fuel glycogen may be consumed by any muscular action as well as by the particular muscular action for which the integration and consequent stimulation were made； that is； if one were provoked to such anger that he felt impelled to attack the object of his anger； one of three things might happen： First； he might perform no physical act but give expression to the emotion of anger； second； he might engage in a physical struggle and completely satisfy his anger； third； he might immediately engage in violent gymnastic exercises and thus consume all the motor…producing elements mobilized by the anger and thus clarify his body。
In these premises we find our explanation of the origin and purpose of laughter and crying； for since they consist almost wholly of muscular exertion； they serve precisely such clarifying purposes as would be