It is apt, like a well-bred creature, to get into a
sort of exalted state under the stimulus of need, so that its owner
feels amazed at the ease of its processes and at the sense of
_wide-awakefulness_ and power that accompanies them. It is only after
very long misuse that the brain begins to have means of saying, "I have
done enough;" and at this stage the warning comes too often in the shape
of some one of the many symptoms which indicate that the organ is
already talking with the tongue of disease.

I do not know how these views will be generally received, but I am sure
that the personal experience of many scholars will decide them to be
correct; and they serve to make clear why it is that men may not know
they are abusing the organ of thought until it is already suffering
deeply, and also wherefore the mind may not be as ruthlessly overworked
as the legs or arms.

Whenever I have closely questioned patients or men of studious habits as
to this matter, I have found that most of them, when in health,
recognized no such thing as fatigue in mental action, or else I learned
that what they took for this was merely that physical sense of being
tired, which arises from prolonged writing or constrained positions. The
more, I fancy, any healthy student reflects on this matter the more
clearly will he recognize this fact, that very often when his brain is
at its clearest, he pauses only because his back is weary, his eyes
aching, or his fingers tired.

This most important question, as to how a man shall know when he has
sufficiently tasked his brain, demands a longer answer than I can give
it here; and, unfortunately, there is no popular book since Ray's clever
and useful "Mental Hygiene," and Feuchtersleben's "Dietetics of the
Soul," both out of print, which deals in a readable fashion with this or
kindred topics.[1] Many men are warned by some sense of want of
clearness or ease in their intellectual processes. Others are checked by
a feeling of surfeit or disgust, which they obey or not as they are
wise or unwise. Here, for example, is in substance the evidence of a
very attentive student of his own mental mechanism, whom we have to
thank for many charming products of his brain. Like most scholars, he
can scarcely say that he ever has a sense of "brain-tire," because cold
hands and feet and a certain restlessness of the muscular system drive
him to take exercise. Especially when working at night, he gets after a
time a s