the adrenals, sympathy and curiosity in relation to the
pituitaries, suggests that a similar explanation will hold for the
dynamics of the other instincts. In the closest relation to the
thyroid appear the instincts first isolated, so to speak, by McDougall
as the instincts of self-display and self-effacement, accompanied
by emotions of pride and shame respectively. In certain states of
excessive thyroid activity there is an extra stimulation of the
instinctive display of the person which may go on to boasting,
mania and exhibitionism. On the other hand, in states of thyroid
insufficiency, depression is produced, which may go on to melancholia,
a desire to be alone, to hide, to sit apart and even a tendency to
accuse the self of various uncommitted crimes and sins. In the form
of cyclic insanity known as the manic-depressive psychosis, mania
alternates with depression, as if the personality were dominated
wholly in turn by one or the other of these two instincts of the ego.
There is a good deal of evidence that behind them is a corresponding
fluctuation in the amount the thyroid secretes into the blood. Among
the thyroid-centered attitudes toward the self gyrate more than in
any other type. Egomania and megalomania occur most often in thyroid
unstable individuals.

ENERGY AND SENSITIVITY

In his classic Inquiries into Human Faculty, Francis Galton laid down
some fundamental considerations concerning energy and sensitivity
as mental traits. Energy he defined as the capacity for labor, and
declared it to be the measure of the fullness of life or vitality.
Statistical study by him of men of genius and their ancestors showed
them to be endowed with a large amount of energy. It has been said to
be the absolute prerequisite of genius. Now if there is a single fact
that has been well established by investigations of the internal
secretions, it is that the energy quantum of an individual is a
function of and determined by his thyroid. The more thyroid he has,
the more energetic will he be--the less thyroid the less energetic,
and the lazier. The thyroid-centered individual, of the excess thyroid
type, actually burns up more food and produces more heat than the
ordinary organism. He burns himself up faster in general.

When the thyroid sends more secretion into the blood, more thyroxin,
it accelerates all the functions and activities of the organs. Tea and
coffee produce loquacity because they stimulate the thyroid. People