ages of a
dictionary. Sir Walter Scott is said to have been troubled in a similar
way. A great lawyer, whom I questioned lately as to this matter, told me
that his cure was a chapter or two of a novel, with a cold bath before
going to bed; for, said he, quaintly, "You never take out of a cold bath
the thoughts you take into it." It would be easy to multiply such
examples.

Looking broadly at the question of the influence of excessive and
prolonged use of the brain upon the health of the nervous system, we
learn, first, that cases of cerebral exhaustion in people who live
wisely are rare. Eat regularly and exercise freely, and there is scarce
a limit to the work you may get out of the thinking organs. But if into
the life of a man whose powers are fully taxed we bring the elements of
great anxiety or worry, or excessive haste, the whole machinery begins
at once to work, as it were, with a dangerous amount of friction. Add to
this such constant fatigue of body as some forms of business bring
about, and you have all the means needed to ruin the man's power of
useful labor.

I have been careful here to state that combined overwork of mind and
body is doubly mischievous, because nothing is now more sure in hygienic
science than that a proper alternation of physical and mental labor is
best fitted to insure a lifetime of wholesome and vigorous intellectual
exertion. This is probably due to several causes, but principally to the
fact that during active exertion of the body the brain cannot be
employed intensely, and therefore has secured to it a state of repose
which even sleep is not always competent to supply. There is a Turkish
proverb which occurs to me here, like most proverbs, more or less true:
"Dreaming goes afoot, but who can think on horseback?" Perhaps, too,
there is concerned a physiological law, which, though somewhat
mysterious, I may again have to summon to my aid in the way of
explanation. It is known as the law of Treviranus, its discoverer, and
may thus be briefly stated: Each organ is to every other as an excreting
organ. In other words, to insure perfect health, every tissue, bone,
nerve, tendon, or muscle should take from the blood certain materials
and return to it certain others. To do this every organ must or ought to
have its period of activity and of rest, so as to keep the vital fluid
in a proper state to nourish every other part. This process in perfect
health is a system of mutual assurance, and