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uct in health and disease could be predicted。 Reaction to environment is the basis of conduct； of moral standards； of manners and conventions； of work and play； of love and hate； of protection and murder； of governing and being governed； in fact； of all the reactions between human beingsof the entire web of life。 As Sherrington has stated； 〃Environment drives the brain； the brain drives the various organs of the body；〃 and here we believe we find the key to a mechanistic interpretation of all body processes。
On this basis we may see that the activities of life depend upon the ability of the parts of the body mechanism to respond adequately to adequate stimulation。 This postulate applies not only to stimuli from visible forces； but to those received by the invasion of the micro…bodies which cause pyogenic or non…pyogenic infections。 In the case of dangerous assaults by visible or invisible enemies； the brain； through the nerves and all parts of the motor mechanism； meets the attack by attempts at adaptation。 Recovery； invalidism； and death depend upon the degree of success with which the attacking or invading enemies are met。 Questions regarding disease become； therefore； questions in adaptation； and it is possible that； when studied in the light of this conception； the key to many hitherto unsolved physical problems may be found。
Perhaps no more convincing proof of our thesis may be secured than by a study of that ever…present phenomenonpain。 In whatever part of the body and by whatever apparent cause pain is produced； we find that it is invariably a stimulation to motor activity whose ultimate object is protection。 Thus by the muscular action resulting from pain we are protected against heat and cold； against too powerful light； against local anemia caused by prolonged pressure upon any portion of the body。 So； too； pain of greater or less intensity compels the required emptying of the pregnant uterus and the evacuation of the intestine and the urinary bladder。
It should be noted that in every instance the muscular activity resulting from pain is specific in its type； its distribution； and its intensity； this specificity being true not only of pain which is the result of external stimulation； but also of the pain associated with certain types of infection。
Pain； however； is not the only symptom of the invasion of the body by pyogenic or parasitic organisms。 Fever； invariably； and chills； often； accompany the course of the infections。 Can these phenomena also be explained as adaptations of the motor mechanism for the good of the individual？
As the phenomena of chills and fever are most strikingly exhibited in malaria； let us study the course of events in that disease。 It is known that the malarial parasite develops in the red blood…corpuscles； and that the chills and fever appear when the cycle of parasitic development is complete and the adults are ready to escape from the corpuscles of the blood plasma。 Bass； of New Orleans； has proved that the favorable temperature for the growth of the malarial organism is 98'0； and that at 102'0 the adult organisms will be killed； though the latter temperature is not fatal to the spores。 The adult life of the malarial parasite begins after its escape into the blood plasma； and it is there that the organism is most susceptible to high temperature。 We must infer； therefore； that the fever is an adaptation on the part of the host for despatching the enemy。
What； then； may be the protective part played by the chill？ A chill is made up of intermittent contractions of all the external muscles of the body。 This activity results in an increase of the body heat and in an anemia of the superficial parts of the body； so that less heat can be lost by radiation。 By this means； therefore； the external portions of the body contribute measurably to the production of the beneficent and saving fever。
It must be remembered that this power of adaptation is not peculiar to man alone； but that it is a quality shared by all living creatures。 While the human body has been adapting itself for self…protection by producing a febrile reaction whereby to kill the invading organisms； the invaders on their side have been adapting themselves for a life struggle within the body of the host。 In these mortal conflicts between invaders and host； therefore； the issue is often in doubt； and sometimes one and sometimes the other will emerge victorious。
We must believe that a similar adaptive response exists in all parasitic infectionsthe cycles varying according to the stages in the development of the invaders。 If the bacteria develop continuously； the fever is constant instead of intermittent； since the adequate stimulus is constantly present。
Bacteriology has taught us that both heat and cold are fatal to pathogenic infections； for this reason either of the apparently contradictory methods of treatment may help； _i。 e_。； either hot or cold applications。 It should be borne in mind； however； that we have to deal not only with the adult organisms； but with the spores also。 The application of cold may keep the spores from developing； while heat may promote their development； and the course of the disease may vary； therefore； according to our choice of treatment。
From this viewpoint； we can understand the intermittent temperature in a patient who is convalescing from an extreme infection； as peritonitis； pylephlebitis； multiple abscess of the liver； etc。 In these conditions there may occur days of normal temperature； followed by an abrupt rise which will last for several days this in turn succeeded by another remittance。 This cycle may be repeated several times； and on our hypothesis we may believe it is caused by the successive development to maturity of spores of varying ages。
If these premises are sound； the wisdom of reducing the temperature in case of infection may well be questioned。
On this mechanistic basis the emotions also may be explained as activations of the entire motor mechanism for fighting； for escaping； for copulating。 * * * * * * * * * * * * * * * * * * * *
The emotions； then； are the preparation for phylogenetic activities （Fig。 48）。 If the activities were consummated； the fuelglycogen and the activating secretions from the thyroid； the adrenals； the hypophysis； would be consumed。 In the activation without action these products must be eliminated as waste products and so a heavy strain is put upon the organs of elimination。 It is obvious that the body under emotion might be clarified by active muscular exercise； but the subject of the emotion is so strongly integrated thereby that it is difficult for him to engage in diverting； clarifying exertion。 * * * * * * * * * * * * * * * * * * * *
So； as we have indicated already； certain deleterious effects are produced when the body mechanism is activated without resultant action。 For example； the output of adrenalin is increased； and； as a consequence； arteriosclerosis and cardiovascular disease may occur in persons who have been subjected to prolonged emotional strain； since it has been proved that the prolo