ergy possessed by the organism is used in its
relation with the ordinary stimuli of its environment."[50] These
men--Professor James and Dr. Sidis--represent not young enthusiasts
who ignorantly fancy that every one shares their own abundant
strength, but careful men of science who have repeatedly been able to
unearth unsuspected supplies of energy in "worn out" men and women,
supposed to be at the end of their resources. Every successful
physician and every leader of men knows the truth of these statements.
What would have happened in the great war if Marshal Foch had not
known that his men possessed powers far beyond their ken, and had not
had sublime faith in the "second wind"?

[Footnote 50: Sidis: P. 112 of the composite volume
_Pychotherapeutics_.]

=What about Being Tired?= If all these things are true, why do people
need to be told? If man's equipment is so adequate and his reserves
are so ample, why after all these centuries of living does the human
race need to learn from science the truth about its own powers? The
average man is very likely to say that it is all very well for a
scientist sitting in his laboratory to tell him about hidden
resources, but that he knows what it is to be tired. Is not the crux
of the whole question summed up in that word "tired"? If we do not
need to rest, why should fatigue exist? If the purpose of fatigue
seems to be to slow down our efforts, why should we disregard it or
seek to evade its warnings? The whole question resolves itself into
this: What is fatigue? In view of the hampering effect of
misconception on this point, it is evident that the question is not
academic, but intensely practical. We shall find that fatigue is of
two kinds,--true and false, or physical and moral, or physiological
and nervous,--and that while the two kinds feel very much alike,
their origin and behavior are quite different.

PHYSIOLOGICAL FATIGUE

=Fatigue, not Exhaustion.= In the first place, then, fatigue very
seldom means a lack of strength or an exhaustion of energy. The
average man in the course of a lifetime probably never knows what it
is to be truly exhausted. If he should become so tired that he could
in no circumstances run for his life, no matter how many wild beasts
were after him, then it might seem that he had drained himself of all
his store of energy. But even in that case, a large part of his
fatigue would be the result of another cause.

=A Matter of Chemistry.= True fat