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tor only when physical force of a certain intensity and rate of motion is applied。 This is true both of the visible contacts affecting the nociceptors and of the invisible contacts by those intangible forces which affect the distance ceptors。 For example； each variation in speed of the light…producing waves of ether causes a specific reaction in the brain。 For one speed of ether waves the reaction is the perception of the color blue； for another； yellow； for another； violet。 Changes in the speed of air waves meet with specific response in the brain patterns tuned to receive impressions through the aural nerves； and so we distinguish differences in sound pitch。 If we can realize the infinite delicacy of the mechanisms adapted to these infinitesimal variations in the speed and intensity of invisible and intangible stimuli； it will not be difficult to conceive the variations of brain patterns which render possible the specific responses to the coarser contacts of visible environment。
Each brain pattern is adapted for but one type of motion； and so the specific stimuli of the innumerable ceptors play each upon its own brain pattern only。 In addition； each brain pattern can react to stimuli applied only within certain limits。 Too bright a light blinds； too loud a sound deafens。 No mechanism is adapted for waves of light above or below a certain rate of speed； although this range varies in different individuals and in different species according to the training of the individual and the need of the species。
We have already referred to the fact that there is no receptive mechanism adapted to the stimuli from the _x_…ray； from the high…speed bullet； from electricity。 So； too； there are innumerable forces in nature which can excite in man no adaptive response； since there exist in man no brain patterns tuned to their waves； as in the case of certain ethereal and radioactive forces。
On this mechanistic basis the emotions may be explained as activations of the entire motor mechanism for fighting； for escaping； for copulating。 The sight of an enemy stimulates in the brain those patterns formed by the previous experiences of the individual with that enemy； and also the experiences of the race whenever an enemy had to be met and overcome。 Each of these many brain patterns in turn activates that part of the body through which lies the path of its own adaptive response those parts including the special energizing or activating organs。 Laboratory experiments show that in an animal driven strongly by emotion the following changes may be seen： （1） A mobilization of the energy…giving compound in the brain…cells； evidenced by a primary increase of the Nissl substance and a later disappearance of this substance and the deterioration of the cells （Figs。 5 and 13）； （2） increased output of adrenalin （Cannon）； of thyroid secretion； of glycogen； and an increase of the power of oxidation in the muscles； （3） accelerated circulation and respiration with increased body temperature； （4） altered metabolism。 All these are adaptations to increase the motor efficiency of the mechanism。 In addition； we find an inhibition of the functions of every organ and tissue that consumes energy； but does not contribute directly to motor efficiency。 The mouth becomes dry； the gastric and pancreatic secretions are lessened or are completely inhibited； peristaltic action stops。 The obvious purpose of all these activations and inhibitions is to mass every atom of energy upon the muscles that are conducting the defense or attack。
So strong is the influence of phylogenetic experience that though an enemy to…day may not be met by actual physical attack； yet the decks are cleared for action； as it were； and the weapons made ready； the body as a result being shaken and exhausted。 The type of emotion is plainly declared by the activation of the muscles which would be used if the appropriate physical action were consummated。 In anger the teeth are set； the fists are clenched； the posture is rigid； in fear the muscles collapse； the joints tremble； and the running mechanism is activated for flight； in sexual excitement the mimicry is as obvious。 The emotions； then； are the preparations for phylogenetic activities。 If the activities are consummated； the fuelglycogenand the activating secretions from the thyroid； the adrenals； the hypophysis are 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。 The person in anger does not want to be saved from the ill effects of his own emotion； he wants only to fight； the person in fear wants only to escape； the person under sexual excitement wants only possession。
All the lesser emotionsworry； jealousy； envy； grief； disappointment； expectationall these influence the body in this manner； the consequences depending upon the intensity of the emotion and its protraction。 Chronic emotional stimulation； therefore； may fatigue or exhaust the brain and may cause cardiovascular disease； indigestion； Graves' disease； diabetes； and insanity even。
The effect of the emotions upon the body mechanism may be compared to that produced upon the mechanism of an automobile if its engines are kept running at full speed while the machine is stationary。 The whole machine will be shaken and weakened； the batteries and weakest parts being the first to become impaired and destroyed； the length of usefulness of the automobile being correspondingly limited。
We have shown that the effects upon the body mechanism of the action of the various ceptors is in relation to the response made by the brain to the stimuli received。 What is this power of response on the part of the brain but CONSCIOUSNESS？ If this is so； then consciousness itself is a reaction to environment； and its intensity must vary with the state of the brain and with the environmental stimuli。 If the brain…cells are in the state of highest efficiency； if their energy has not been drawn upon； then consciousness is at its height； if the brain is fatigued； that is； if the energy stored in the cells has been exhausted to any degree； then the intensity of consciousness is diminished。 So degrees of consciousness vary from the height maintained by cells in full vigor through the stages of fatigue to sleep； to the deeper unconsciousness secured by the administration of inhalation anesthetics； to that complete unconsciousness of the environment which is secured by blocking the advent to the brain of all impressions from both distance and contact ceptors； by the use of both local and inhalation anestheticsthe state of anoci…association （Fig。 14）。
Animals and man may be so exhausted as to be only semi…conscious。 While a brain perfectly refreshed by a long sleep cannot immediately sleep again； the exhausted brain and the refreshed brain when subjected to equal stimuli will rise to unequal heights of consciousness。 The nature of the physical basis of consciousness has be