trigonometry will,
though in the same condition, stay up studying football
strategy, rehearsing for a varsity show, or getting out the
next morning's edition of his college paper. "If each man
did the mental work for which he was fit, and which he
enjoyed, men would work willingly much longer than they now
do."[1*] The effects of mental fatigue are, when analyzed, due
chiefly to the physically injurious effects that do, but do not
necessarily, accompany mental work.

[Footnote 1: T. Arai: _Mental Fatigue_.]

[Footnote 2: Thorndike: _Educational Psychology_, Briefer Course, p. 322.]

[Footnote 1*: Thorndike: _Educational Psychology_, Briefer Course, p. 326.]

Proper air and light, proper posture and physical exercise, enough
food and sleep, and work whose purpose is rational, whose difficulty
is adapted to one's powers, and whose rewards are just, should be
tried before recourse to the abandonment of work itself. It is indeed
doubtful if sheer rest is the appropriate remedy for a hundredth part
of the injuries that result from mental work in our present irrational
conduct of it.[2]

[Footnote 2: _Ibid_., p. 328.]

The study of the conditions of mental work seems to reveal,
in brief, that the conditions of fatigue are essentially physical
in character. Given adequate physical conditions, in particular
guarding against eye-strain, over-excitement (which means
distraction from the work in hand), and loss of sleep, mental
work is itself peculiarly unaffected by fatigue conditions. The
degree in which mental work can be persisted in depends,
therefore, other things being equal, on the individual's own
interests, the number and intensity of rival interests which
persist during a given piece of mental work, and the habits of
mind with which the individual approaches his work.

The experimental demonstration that so-called mental
fatigue is largely physical in its conditions has thus a dual
significance. It indicates how arduous and persistent mental
endeavor may be and how wide are the possibilities of intellectual
accomplishment. It is an important fact for human life
that the brain is possibly the most tireless part of the human
machine. What seems to be mental fatigue can be materially
reduced if the physical conditions under which studying,
writing, and all other kinds of mental work are performed are
carefully regulated. Another large part of what passes for
mental fatigue will be removed if the individual becom