consciousness _because the livelier environment brings about a more
rapid reproduction of memory pictures_.

And here comes a particularly striking fact. One would naturally
suppose that the more energy a man consumed, and the faster he lived,
the more quickly his vitality would be exhausted and the shorter his
life would be.

As a matter of fact, by the divine beneficence of Providence, _your
organism is so ordered as to adapt itself within certain wide limits
to the demands made upon it_.

[Sidenote: _Fast Living and Long Living_]

You may call into play all the stored-up resources of your being and
still not stake everything upon a single throw. For the supply of
mental energy is as inexhaustible as the reservoir of all past
experience, while the supply of physical energy involved in brain and
nerve activity is, like the immortal liver of Prometheus, renewed as
fast as depleted.

Two sets of facts that have been established by elaborate scientific
experiment will convince you of the truth of these propositions.

[Sidenote: _Professor Patrick's Experiments_]

Professor Patrick, of the State University of Iowa, conducted some of
these experiments. He caused three young men to remain awake for four
successive days and nights. They were then allowed to go to sleep, the
purpose of the experiment being to determine just how much time Nature