he
fatigue-obstacle usually obeyed. There may be layer after layer of
this experience. A third and a fourth "wind" may supervene. Mental
activity shows the phenomenon as well as physical, and in exceptional
cases we may find, beyond the very extremity of fatigue-distress,
amounts of ease and power that we never dreamed ourselves to
own,--sources of strength habitually not taxed at all, because
habitually we never push through the obstruction, never pass those
early critical points.

For many years I have mused on the phenomenon of second wind, trying to
find a physiological theory. It is evident that our organism has
stored-up reserves of energy that are ordinarily not called upon, but
that may be called upon: deeper and deeper strata of combustible or
explosible material, discontinuously arranged, but ready for use by
anyone who probes so deep, and repairing themselves by rest as well as
do the superficial strata. Most of us continue living unnecessarily
near our surface. Our energy-budget is like our nutritive budget.
Physiologists say that a man is in "nutritive equilibrium" when day
after day he neither gains nor loses weight. But the odd thing is that
this condition may obtain on astonishingly different amounts of food.
Take a man in nutritive equilibrium, and systematically increase or
lessen his rations. In the first case he will begin to gain weight, in
the second case to lose it. The change will be greatest on the first
day, less on the second, less still on the third; and so on, till he
has gained all that he will gain, or lost all that he will lose, on
that altered diet. He is now in nutritive equilibrium again, but with
a new weight; and this neither lessens nor increases because his
various combustion-processes have adjusted themselves to the changed
dietary. He gets rid, in one way or another, of just as much N, C, H,
etc., as he takes in _per diem_.

Just so one can be in what I might call "efficiency-equilibrium"
(neither gaining nor losing power when once the equilibrium is reached)
on astonishingly different quantities of work, no matter in what
direction the work may be measured. It may be physical work,
intellectual work, moral work, or spiritual work.

Of course there are limits: the trees don't grow into the sky. But the
plain fact remains that men the world over possess amounts of resource
which only very exceptional individuals push to their extremes of use.
But the very same ind