the
action of external powers on the excitability; without excitability
these stimulants would produce no effect, and whatever may be the
nature of the excitability, or however abundant it may be, still,
without the action of external powers, no life is produced.

From what has been said, we may see the reason why life is in a
languid state in the morning: It acquires vigour by the gradual and
successive application of stimuli in the forenoon: It is in its most
perfect state about midday, and remains stationary for some hours:
From the diminution or exhaustion of the excitability, it lessens in
the evening, and becomes more languid at bed time; when, from defect
of excitability, the usual exciting powers will no longer produce
their effect, a torpid state ensues, which we call sleep, during
which, the exciting powers cannot act upon us; and this diminution of
their action allows the excitability to accumulate; and, to use the
words of Dr. Armstrong,

"Ere morn the tonic, irritable nerves
Feel the fresh impulse, and awake the soul."

LECTURE X.
THE LAWS OF ANIMAL LIFE, CONTINUED.

In the last lecture I began to investigate the laws by which living
bodies are governed, and the effects produced by the different
exciting powers, which support life, upon the excitability, or vital
principle. The facts which we examined led us to two conclusions,
which, when properly applied, we shall find will explain most of the
phenomena of life, both in health, and in disease. The conclusions
alluded to, are these: when the exciting powers have acted more
feebly, or weakly, than usual, for some time; or when their action is
withdrawn, the excitability accumulates, and becomes more powerfully
affected by their subsequent action. And, on the contrary, when the
action of these powers has been exerted with violence, or for a
considerable time, the excitability becomes exhausted, and less fit
to receive their actions.

A number of facts were mentioned in proof of these conclusions, and a
great number more might have been brought forwards, could it have
served any other purpose than to have taken up our time, which I hope
may be better employed.

This exhaustion of the excitability, by stimulants, may either be
final, or temporary. We see animals, while the exciting powers
continue to act, at first appear in their greatest vigour, then
gradually decay, and at last come into that state, in which, from the
long continued action of