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Natural Selection and Chemical Noci…association in the Infections
Thus far we have considered the behavior of the individual as a whole in his response to a certain type of noci…influences。 We have been voicing our argument in terms of physical escape from GROSS physical dangers； or of grappling with GROSS NERVE…MUSCULAR enemies of the same or of other species。 To explain these phenomena we have invoked the aid of the laws of natural selection and phylogenetic association。 If our conclusions be correct； then it should follow that in the same laws we may find the explanation of immunity； which； of course； means a defensive response to our MICROSCOPIC enemies。 There should be no more difficulty in evolving an efficient army of phagocytes by natural selection； or in developing specific chemical reactions against _*microscopic enemies_； than there was in evolving the various nociceptors for our nerve…muscular defense against our _*gross enemies_。 That immunity is a chemical reaction is no argument against the application of the law of natural selection or of association。 What essential difference is there between the chemical defense of the skunk against its NERVE…MUSCULAR enemies and its chemical defense （immunity） against its MICROSCOPIC ENEMIES？
The administration of vaccines becomes the adequate stimulus which awakens phylogenetic association of a chemical nature as a result of which immune bodies are produced。
In discussing this subject I will raise only the question whether or not the specific character of the inaugural symptoms of some infectious diseases may be due to phylogenetic association。 These inaugural symptoms are measurably a recapitulation of the leading phenomena of the disease in its completed clinical picture。 Thus； the furious initiative symptoms of pneumonia； of peritonitis； or erysipelas； of the exanthemata； are exaggerations of phenomena which are analogous to the phenomena accompanying physical injury and fear of physical violence。 Just as the acute phenomena of fear； or those which accompany the adequate stimulation of nociceptors； are recapitulations of phylogenetic struggles； so may the inaugural symptoms of an infection be a similar phylogenetic recapitulation of the course of the disease。 A certain amount of negative evidence is supplied by a comparison of the response to a dose of toxins with the response to a dose of a standard drug。 No drug in therapeutic dosage except the iodin compounds causes a febrile response； no drug causes a chill； on the other hand； all specific toxins cause febrile responses and many cause chills。 If a species of animal had been poisoned by a drug during vast periods of time； and if natural selection had successfully established a self…defensive response； then the administration of that drug would cause a noci…association （chemical）； and a specific reaction analogous to that following the administration of Coley's toxins might be expected。 Bacterial noci…association probably operates through the same law as that through which physical noci…association operates。 Natural selection is impartial； however。 It must be supposed that it acts impartially upon the microscopic invader and upon the host。 On this ground one must infer that； in accordance with the same law of natural selection； the bacteria of acute infections have met by natural selection each advance in the struggle of the host for immunity。 Hence the fast and furious struggle between man and his microscopic enemies merely indicates to what extent natural selection has developed the ATTACK and the DEFENSE respectively。 This struggle is analogous to the quick and decisive battles of the carnivora when fighting among themselves or when contending against their ancient enemies。 But when phylogenetically strange animals meet each other； they do not understand how to conduct a fight： natural selection has not had the opportunity of teaching them。 The acute infections have the characteristics of being ancient enemies。 On this hypothesis one can understand the high mortality of measles when it is introduced into a new country。 By natural selection； measles has become a powerful enemy of the human race； and a race to which this infection is newly introduced has not had the advantage of building up a defense against it by the law of natural selection。 May not the phenomena of anaphylaxis be studied on associational lines？ Then； too； there may be chemical noci…associations with enemies now extinct； which； like the ticklish points； may still be active on adequate stimulation。 This brief reference to the possible relation of the phenomena of the acute infections to the laws of natural selection and of specific chemical noci…association has been made as a suggestion。 Since the doctrine of evolution explains all or nothing； I have included many phenomena to see how reasonable or unreasonable such an explanation might be。
Recapitulation
The following are the principal points presented： In operations under inhalation anesthesia the nerve impulses from the trauma reach every part of the brainthe cerebrum that is apparently anesthetized as well as the medulla that is known to remain awake the proof being the PHYSIOLOGIC exhaustion of and the PATHOLOGIC change in the nerve…cells。 Under ether anesthesia the damage to the nerve…cells is at least four times greater than under nitrous oxid。 Inhalation anesthesia is； therefore； but a veneer a mask that 〃covers the deep suffering of the patient。〃 The cause of the exhaustion of the brain is the discharge of nervous energy in a futile effort to energize the paralyzed muscles in an attempt to escape from the injury just as if no anesthetic had been given。 The exhaustion is； therefore； of the same nature as that from overexertion； but if the nerve…paths connecting the field of operation and the brain be blocked； then there is no discharge of nervous energy from the trauma； and consequently there is no exhaustion； however severe or prolonged the operation may be。
Fear is a factor in many injuries and operations。 The phenomena of fear probably are exhibited only by animals whose natural defense is nerve…muscular。 The skunk； the porcupine； the turtle； have little or no fear。 Fear is born of the innumerable injuries which have been inflicted in the course of evolution。 Fear； like trauma； may cause physiologic exhaustion of and morphologic changes in the brain…cells。 The representation of injury； which is fear； being elicited by phylogenetic association； may be prevented by the exclusion of the noci…association or by the administration of drugs like morphin and scopolamin； which so impair the associational function of the brain…cells that immunity to fear is established。 Animals whose natural defense is in muscular exertion； among which is man； may have their dischargeable nervous energy exhausted by fear alone； or by trauma alone； but most effectively by the combination of both。 What is the mechanism of this discharge of energy？ It is the adequate stimulation of the nociceptors and the physiologic response for the purpose of self…preservation。 According to Sherrington； the nervous system responds in action as a whole and to but one stimulus at a time。 The int