to stimuli, especially to trauma and to fear and to the administration
of thyroid extract. It has been shown that the various causes
of the discharge of nervous energy produce alterations in the nervous
system and probably in the thyroid gland. This is especially
true of the fear stimulus, and has been clearly demonstrated
in the brains of rabbits which had been subjected to fear alone
(Fig. 13). Of special interest was the effect of daily fright.
In this case the brain-cells showed a distinct change, although the animal
had been subjected to no fear for twenty-four hours before it was killed
(Fig. 13 C. Now, a great distinction between man and the lower
animals is the greater control man has acquired over his actions.
This quality of control, having been phylogenetically most recently
acquired, is the most vulnerable to various NOCUOUS influences.
The result of a constant noci-integration may be a wearing-out
of the control cells of the brain. In a typical case of Graves'
disease a marked morphologic change in the brain-cells has
been demonstrated (Fig. 15). As has been previously stated,
the origin of many cases of Graves' disease is associated
with some noci-influence. If this influence causes stimulation
of both the brain and the thyroid, its excessive action may cause
impairment of the brain and also hyperplasia of the thyroid.
As self-control is impaired, fear obtains an ascendency and,
_pari passu_, stimulates the thyroid still more actively (Fig. 16).
Finally, the fear of the disease itself becomes a noci-stimulus.
As the thyroid secretion causes an increase in the facility
with which nervous energy is discharged, a pathologic reciprocal
interaction is established between the brain and the thyroid.
The effect of the constantly recurring stimulus of the noci-influence
is heightened by summation. This reciprocal goading may
continue until either the brain or the thyroid is destroyed.