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ure be low； there will be a permanent loss of some of the brain…cells。 This explains why an individual who has suffered from a prolonged hemorrhage will never again be restored to his original powers。
Drugs。According to their effect upon the brain…cells； drugs may be divided into three classes： First； those that stimulate the brain…cells to increased activity； as strychnin （Fig。 37）； second； those that chemically destroy the brain…cells； as alcohol and iodoform （Figs。 38 and 39）； third； those that suspend the functions of the cells without damaging them； as nitrous oxid； ether； morphin。 Our experiments have shown that the brain…cell changes induced by drugs of the first class are precisely the same as the cycle of changes produced by the emotions and by physical activity。 We have found that strychnin； according to the dosage； causes convulsions ending in exhaustion and death； excitation followed by lassitude； stimulation without notable after…results； or
｛illust。 caption = A； Section of Cerebellum of Normal Dog。 C； Section of Cerebellum of Dog after Repeated Doses of Strychnin。 FIG。 37。 BRAIN…CELLS SHOWING STAGE OF HYPERCHROMATISM FOLLOWED BY CHROMATOLYSIS RESULTING FROM THE CONTINUATION OF THE STIMULUS。 （Camera lucida drawings。）increased mental tone； while the brain…cells accurately display these physiologic alterations in proportional hyperchromatism in the active stages； and proportional chromatolysis in the stages of reaction。 The biologic and therapeutic application of this fact is as obvious as it is important。
In our experiments； alcohol in large and repeated dosage caused marked morphologic changes in the brain…cells which went as far even as the destruction of some of the cells （Fig。 39）。 Ether； on the other hand； even after five hours of administration； produced no observable destructive changes in the brain…cells。
The effect of iodoform was peculiarly interesting； as it was the only drug that produced a rise of temperature。 Its observed effect upon the brain…cells was that of wide…spread destruction。
Infections。In every observation regarding the effect of pyogenic infections on dogs and on man we found that they caused definite and demonstrable lesions in certain cells of the nervous system； the most marked changes being in the cortex and the cerebellum （Fig。 40）。 For example； in fatal infections resulting from bowel obstruction； in peritonitis； and in osteomyelitis； the real lesion is in the brain…cells。 We may； therefore； reasonably conclude that the lassitude； the diminished mental power； the excitability； irritability； restlessness； delirium； and unconsciousness which may be associated with acute infections； are due to physical changes in the brain…cells。
Graves' Disease。In Graves' disease the brain…cells show marked changes which are apparently the same as those produced by overwork； by the emotions； and by strychnin。 In the postmortem examination of one advanced case it was found that a large number of brain…cells were disintegrated beyond the power of recuperation； even had the patient lived。 This is undoubtedly the reason why a severe case of exophthalmic goiter sustains a permanent loss of brain power。
Insomnia。The brains of rabbits which had been kept awake for one hundred hours showed precisely the same changes as those shown in physical fatigue； strychnin poisoning； and exhaustion from emotional stimulation。 Eight hours of continuous sleep restored all the cells except those that had been completely exhausted。 This will explain the permanent ill effect of long…continued insomnia； that is； long…continued insomnia permanently destroys a part of the brain…cells just as do too great physical exertion； certain drugs； emotional strain； exophthalmic goiter； and hemorrhage。 We found； however； that if； instead of natural sleep； the rabbits were placed for the same number of hours under nitrous oxid anesthesia； not only did the brain…cells recover from the physical deterioration； but that 90 per cent。 of them became hyperchromatic。 This gives us a possible clue to the actual chemical effect of sleep。 For since nitrous oxid owes its anesthetic effect to its influence upon oxidation； we may infer that sleep also retards the oxidation of the cell contents。 If this be true； then it is probable that inhalation anesthetics exert their peculiar influence upon that portion of the brain through which sleep itself is produced。 If nitrous oxid anesthesia and sleep are chemically identical； then we have a further clue to one of the primary mechanisms of life itself； and as a practical corollary one might be able to produce artificial sleep which would closely resemble normal sleep； but which would have this advantage； that by using an anesthetic which interferes with oxidation the brain…cells might be reconstructed after physical fatigue； after emotional strain； or after the depression of disease。
In the case of the rabbit in which nitrous oxid was substituted for sleep； the appearance of the brain…cells resembled that in but one other group experimentally examinedthe brain…cells of hibernating woodchucks。
Insanity。Our researches have shown that in the course of a fatal disease and in fatal exhaustion； however produced； death does not ensue until there is marked disorganization of the brain tissue。 In the progress of disease or exhaustion one may see in different patients every outward manifestation of mental deterioration； manifestations which； in a person who does not show any other sign of physical disease； mark him as insane。 Take； for example； the progressive mental state of a brilliant scholar suffering from typhoid fever。 On the first day of the gradual onset of the disease he would notice that his mental power was below its maximum efficiency； on the second he would notice a further deterioration； and so the mental effect of his disease would progress until he would find it impossible to express a thought or to make a deduction。 No one can be philanthropic with jaundice； no one suffering from Graves' disease can be generous； no mental process is possible in the course of the acute infectious diseases。 Just prior to death from any cause every one is in a mental state which； if it could be continued； would cause that individual to be judged insane。 If the delirium that occurs in the course of certain diseases should be continued； the patient would be judged insane。 In severe cases of Graves' disease the patient is insane。 Individuals under overwhelming emotion may be temporarily insane。 Every clinician has seen great numbers of cases in which insanity is a phase of a disease； of an injury； or of an emotion。 The stage of excitation in anesthesia is insanity。 The only difference between what is conventionally called insanity and the fleeting insanity of the sick and the injured is that of time。 We may conclude； therefore； what must be the brain…picture of the person who is permanently insane。 This _a priori_ reasoning is all that is possible； since the study of the brain in the insane has thus far been confined to the brains of those who have died of some disease。 And it is impossible to say which changes have been produced by the fatal disease； and which by the condition which produced the insanity。 The only logical way by which to investigate the physical basis of insanity would be to make use of the very rare opportunities of studying the brains of insane persons who have died in accidents。
Our experiments have proved conclusively that whether we call a person fatigued or diseased； the brain…cells undergo physical deterioration； accompanied by loss of mental power （Figs。 40 to 43）。 Even to the minutest detail we can show a direct relationship between the physical state of the brain…cells and the mental power of the individual； that is； the physical power of a person goes _pari passu_ with his mental power。 Indeed； it is impossible to conceive how any mental action； however subtle； can occur without a corresponding change in the brain…cells。 It is possible now to measure only the evidences of the effects on the brain…cells of gross and violent mental activity。 At some future time it will doubtless be possible so to refine the technic of brain…cell examinations that more subtle changes may be measured。 Nevertheless； with the means at our disposal we have shown already that in all the conditions which we have studied the cells of the cortex show the greatest changes； and that loss of the higher mental functions invariably accompanies the cell deterioration。
A MECHANISTIC VIEW OF PSYCHOLOGY＇*＇
＇*＇ Address delivered before Sigma Xi； Case School of Science； Cleveland； Ohio； May 27； 1913； and published in _Science_； August 29； 1913。
Traditional religion； traditional medicine； and traditional psychology have insisted upon the existence in man of a triune nature。 Three 〃ologies〃 have been developed for the study of each nature as a separate entitybody； soul； and spiritphysiology； psychology； theology； physician； psychologist； priest。 To the great minds of each class； from the days of Aristotle and Hippocrates on； there have come glimmerings of the truth that the phenomena studied under these divisions were interrelated。 Always； however； the conflict between votaries of th