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Functional Study of the Adrenals。Our method of applying the Cannon test for adrenalin was as follows： （_a_） The blood of the animals was tested before the application of the stimulus。 If this test was negative； then （_b_） the stimulus was applied and the blood again tested。 If this second test was negative； a small amount of adrenalin was added。 If a positive reaction was then given； the negative result was accepted as conclusive。 （_c_） If the control test was negative； then the stimulus was given。 If the blood after stimulation gave a positive result for adrenalin； a second test of the same animal's blood was made twenty…five minutes or more later。 If the second test was negative； then the positive result of the first test was accepted as conclusive。
We have recorded 66 clear…cut experiments on dogs； which show that after fear and rage； after anaphylaxis； after injections of indol and skatol； of leucin and creatin； of the toxins of diphtheria and colon bacilli； of streptococci and staphylococci； of foreign proteins； and of strychnin； the Cannon test for adrenalin was positive。 The test was negative after trauma under anesthesia； and after intravenous injections of thyroid extract； of thyroglobin； and of the juices of various organs injected into the same animal from which the organs were taken。 Placental extract gave a positive test。 The test was sometimes positive after electric stimulation of the splanchnic nerves。 On the other hand； if the nerve supply to the adrenals had been previously divided； or if the adrenals had been previously excised； then the Cannon test was negative after the administration of each of the foregoing adequate stimuli。 Blood taken directly from the adrenal vein gave a positive result； but under deep morphinization the blood from the adrenal vein was negative； and under deep morphinization the foregoing adequate stimuli were negative。
In brief； the agencies that in our brain…cell studies were found to cause hyperchromatism followed by chromatolysis gave positive results in the Cannon test for adrenalin （Fig。 62）。 The one agent which was found to protect the brain against changes in the Nissl substance morphingave a negative result in the Cannon test for adrenalin。 After excision of the adrenals； or after division of their nerve supply； all Cannon tests for adrenalin were negative。
Histologic Study of the Adrenals。Histologic studies of the adrenals after the application of the adequate stimuli which gave positive results to the Cannon test for adrenalin are now in progress； and thus far the histologic studies corroborate the functional tests。
In hibernating woodchucks； the cells of the adrenal cortex were found to be vacuolated and shrunken。 In one hundred hours of insomnia； in surgical shock； in strong fear； in exhaustion from fighting； after peptone injections； in acute infections； the adrenals undergo histologic changes characteristic of exhaustion （Figs。 66 to 67）。
We have shown that brain and adrenal activity go hand in hand； that is； that the adrenal secretion activates the brain； and that the brain activates the adrenals。 The fundamental question which now arises is this： Are the brain and the adrenals interdependent？ A positive answer may be given to this question； for the evidence of the dependence of the brain upon the adrenals is as clear as is the evidence of the dependence of the adrenals upon the brain。 （1） After excision of the adrenals； the brain…cells undergo continuous histologic and functional deterioration until death。 During this time the brain progressively loses its power to respond to stimuli and there is also a progressive loss of muscular power and a diminution of body temperature。 （2） ｛illust。 caption = FIG。 66。In our crossed circulation experiments we found that adrenalin alone could cause increased brain activity； while histologically we know that adrenalin alone causes an increase of the Nissl substance。 An animal； both of whose adrenals had been excised； showed no hyperchromatism in the brain…cells after the injection of strychnin； toxins； foreign proteins； etc。 （3） When the adrenal nerve supply is divided （Cannon…Elliott）； then there is no increased adrenal activity in response to adequate stimuli。
From these studies we are forced to conclude not only that the brain and adrenals are interdependent； but that the brain is actually more dependent upon the adrenals than the adrenals upon the brain； since the brain deteriorates progressively to death without the adrenals； while the adrenal whose connection with the brain has been broken by the division of its nerve supply will still produce sufficient adrenalin to support life。
From the strong affinity of the brain…cells for adrenalin which was manifested in our experiments we may strongly suspect that the Nissl substance is a volatile； extremely unstable combination of certain elements of the brain…cells and adrenalin； because the adrenals alone do not take the Nissl stain and the brain deprived of adrenalin also does not take Nissl stain。 The consumption of the Nissl substance in the brain…cells is lessened or prevented by morphin； as is the output of adrenalin； and the consumption of the Nissl substance is also lessened or prevented by nitrous oxid。 But morphin does not prevent the action of adrenalin injected into the circulation； hence the control of morphin over energy expenditure is exerted directly on the brain…cells。 Apparently morphin and nitrous oxid both act through this interference with oxidation in the brain。 We； therefore； conclude that within a certain range of acidity of the blood adrenalin can unite with the brain…cells only through the mediation of oxygen； and that the combination of adrenalin； oxygen； and certain brain…cell constituents causes the electric discharge that produces heat and motion。 In this interrelation of the brain and the adrenals we have what is； perhaps； the master key to the automatic action of the body。 Through the special senses environmental stimuli reach the brain and cause it to liberate energy； which in turn activates certain other organs and tissues； among which are the adrenals。 The increased output of adrenalin activates the brain to still greater activity； as a result of which again the entire sympathetic nervous system is further activated； as is manifested by increased heart action； more rapid respiration； raised blood…pressure； increased output of glycogen； increased power of the muscles to metabolize glucose； etc。
If this conclusion be well founded； we should find corroborative evidence in histologic changes in that great storehouse of potential energy； the liver； as a result of the application of each of the adequate stimuli which produced brain…cell and adrenal changes。
The Liver
Prolonged insomnia； prolonged physical exertion； infections； injections of toxins and of strychnin； rage and fear； physical injury under anesthesia； in fact； all the adequate stimuli which affected the brain and the adrenals； produced constant and identical histologic changes in the liverthe cells stained poorly； the cytoplasm was vacuolated； the nuclei were crenated； the cell membranes were irregular； the most marked changes occurring in the cells