s may be thus
obtained. After a time, the electric shocks cannot cause a greater
contraction, but only a lesser. And if continued, the muscle will
cease to function because of fatigue. If now, when the muscle begins
to lag in its response, and its contractions to decrease, one injects
into a vein extracts of thyroid, parathyroid, or adrenal glands, they
will immediately reinvigorate the failing contractions. The injections
must be made before the fatigue is carried to the point of absolute
exhaustion. It follows that these glands normally pour into the
circulation substances which counteract the effect of fatigue
substances, and in fact make possible muscular recuperation from
fatigue throughout the day as well as in emergencies and crises.

Fatigue, conventionally recognized, is something acute and urgent. As
such it means a violent draining of the endocrine wells. But there
is also a chronic fatigue, which has been dignified with the name of
Fatigue Disease. Bernard Shaw once asked for someone to tell him
the name of the germ causing the symptoms of overwork. That being
impossible, he will have to be satisfied with the answer that it is
not a germ, but an internal secretion, or rather a defect of internal
secretion that is the cause.

Whether or not the adrenals have been damaged by past experiences,
and upon their capacity to respond to the necessities of an occasion,
fatigue reactions primarily depend. A quotation from Sir James
MacKenzie, most distinguished of modern English students of medicine,
summarizes the matter neatly. "Abelous, and Langlois and Albanese have
studied the relation of the adrenal bodies to fatigue.... They infer
that the muscular weakness following removal of the adrenals is due
to toxic substances. In view of our present knowledge of the
physiological action of adrenaline in its various forms, it seems more
probable that the weakness is to be explained by the absence of the
normal tone producing internal secretions of the bodies in question."
In other words, the adrenals regulate muscle tone. They produce
nature's tonics for weary tissues. The chronic lassitude of thousands
of our generation, suffering from "that tired feeling," may be put
down to chronic adrenal insufficiency.

It requires no superlative imagination to see that an adrenal poor
subject does not belong upon a job that involves muscle stress over a
long period, or indeed fatiguing conditions of any sort. Nor that a
thyroid