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Unfortunately, the thyroid cannot be studied to advantage either functionally or histologically, for there is as yet no available test for thyroid secretion in the blood as there is for adrenalin, and thyroid activity is not attended by striking histologic changes.
But intelligence does not depend on the whole body; its superior or inferior development is related to a certain corresponding complexity in the surface, volume, and histologic structure of the nervous centres. It happens with the cerebral as with the other functions.
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 In prolonged insomnia the striking changes in the liver were repaired by one seance of sleep.
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.
To prove this relation, we administered the above-mentioned stimuli to animals and studied their effects upon the adrenals by functional, histologic, and surgical methods, the functional tests being made by Cannon's method. Functional Study of the Adrenals. If this second test was negative, a small amount of adrenalin was added.
Whether or not the consequent functional depression and the morphologic alterations seen in the brain-cells may be due to the low blood-pressure which follows excessive trauma is shown by the following experiments: The circulation of animals was first rendered STATIC by over-transfusion, and was controlled by a continuous blood-pressure record on a drum, the factor of anemia being thereby wholly excluded during the application of the trauma and during the removal of a specimen of brain tissue for histologic study.
Histologic examinations of the brains of both dogs showed marked hyperchromatism in the brain receiving adrenalin, while the brain receiving no adrenalin showed no change. Here is a clear-cut observation on the action of adrenalin on the brain, for both the functional and the histologic tests showed that adrenalin causes increased brain action.
That in fear and in injury the thyroid, in cases of Graves' disease, is probably stimulated to increased activity is indicated by the increased activity of the thyroid circulation, by an increase in the size of the gland, by the histologic appearance of activity in the nuclei of the cells, and by an increase of the toxic symptoms.
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. After excision of the adrenals, the brain-cells undergo continuous histologic and functional deterioration until death.
We have seen that adrenalin causes activation of the body connected with its brain by the nervous system, and histologic changes in the brain acted on directly by the adrenalin, but we found no notable brain-cell changes in the other brain through which the products of metabolism have circulated.
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