time, the excitability is exhausted, or becomes less fit
to receive their actions. There are therefore three states in which
living bodies exist. First, a state of accumulated excitability.
Secondly, a state of exhausted excitability. Thirdly, when the
excitability is in such a state as to produce the strongest and most
healthy actions, when acted upon by the external powers.

From what has been said, it must be evident that life depends
continually on the action of external powers on the excitability, and
that by their continued action, if they be properly regulated, the
excitability will be gradually, and insensibly exhausted, and life
will be resigned into the hands of him who gave it, without a
struggle, and without a groan.

We see then that nature operates in supporting the living part of the
creation, by laws as simple and beautiful as those by which the
animated world is governed. In the latter we see the order and
harmony which is observed by the planets, and their satellites, in
their revolution round the great source of heat and light;

"---------- all combin'd
And ruled unerring, by that Single Power,
Which draws the stone projected, to the ground.

In the animated part of the creation, we observe those beautiful
phenomena which are exhibited by an almost infinite variety of
individuals; all depending upon, and produced by one simple law; the
acting of external powers upon their excitability.

I cannot express my admiration of the wisdom of the Creator better
than in the words of Thomson.

"O unprofuse magnificence divine!
O wisdom truly perfect! thus to call
From a few causes such a scheme of life;
Effects so various, beautiful, and great."

Life then, or those functions which we call living, are the effects
of certain exciting powers acting on the excitability, or property
distinguishing living from dead matter. When these effects, viz. the
functions, flow easily, pleasantly, and completely, from the action
of these powers, they indicate that state which we call health.

We may therefore, as we before hinted, distinguish three states of
the irritable fibre, or three different degrees of excitability, of
which the living body is susceptible.

1. The state of health which is peculiar to each individual, and
which has been called by Haller, and other physiologists, the tone of
the fibre. This is produced by a middle degree of stimulus acting
upon a middle degree of excitabili