tissue and functions. Experimental studies do show
that "nervous fatigue is an undoubted fact"[2] and that "we
cannot deny fatigue to the psychic centers"[3] which, like any
other part of the organism are subject to deterioration by
fatigue toxins. Most students report, however, a higher degree
of resistance to fatigue in the nerve fibers than in the
muscles, and a like high resistance to fatigue in the brain
centers.[4]

[Footnote 2:
Frederick S. Lee: "Physical Exercise from the Standpoint of Physiology,"
_Science_, N.S., vol. XXIX, no. 744, p. 525.]

[Footnote 3: Lee: _Fatigue_. Harvey Lectures, 1905-06, p. 180.]

[Footnote 4:
For a summary of nervous fatigue and extensive bibliography, see Goldmark:
_loc. cit._, p. 32.]

The conditions of mental fatigue, however, can be by no
means as simply described as those of physical fatigue. Elaborate
experiments by Professor Thorndike and others tend to
show that, in the strictest sense of the term, there is no such
thing as mental fatigue. That is, any mental function may
be performed for several hours with the most negligible decrease
in the efficiency of the results attained. The subject of
one experiment kept continuously for seven hours performing
mental multiplications of four-place numbers by four-place
numbers with scarcely any perceptible decrease in speed or
accuracy in results.[1] Professor Thorndike draws from this
and similar experiments the conclusion that it is practically
impossible to impair the efficiency of any mental function as
such. What happens when we say our mental efficiency is
being impaired is rather that we _will not_ than that we _cannot_
perform any given mental function. The causes of loss of
efficiency are rather competing impulses[2] than fatigue in
specific mental functions. We are tired _of_ the work, not _by_
it. Continuous mental work of any given kind, writing a
book, solving problems in calculus, translating French, etc.,
involves our being withheld from other activities, games,
music, or companionship, to which by force of habit or
instinct, we are diverted, and diverted more acutely the more
we remain at a fixed task. That it is not mental "fatigue" so
much as distraction that prevents us from persisting at work
is evidenced in the longer time we can stick to work that
really interests us than to tasks in which we have only a
perfunctory or compulsory interest. The college student who is
"too dead tired" to stay up studying