h black and coagulated blood: this organ, and most of
the muscles had nearly lost the whole of their irritability, for they
contracted but very weakly, on the application of the strongest
stimulants.

A quantity of carbonic acid gas was injected into the jugular vein of
a dog: the animal became sleepy, and died in about a quarter of an
hour: the heart was found filled with black and coagulated blood, and
had lost the whole of its irritability; neither it, nor any of the
muscles producing any contractions, upon the application of
stimulants.

Humboldt likewise mentions a curious fact, which tends strongly to
confirm this idea. When the excitability of the limb of a frog had
been so far exhausted, by the application of zinc and silver, that it
would produce no more contractions, on moistening it with oxygenated
muriatic acid, the contractions were renewed.

After the excitability of the sensitive plant (mimosa pudica) had
been so far exhausted, by irritation, that it ceased to contract,
when further irritated, I restored this excitability, and brought it
to a very high degree of irritability, by moistening the earth in
which it grew with oxygenated muriatic acid. Seeds likewise vegetate
more quickly when moistened with this acid, than when they are not.

In short, we shall find, first, that every thing which increases the
quantity of oxygen in organized bodies, increases at the same time
their excitability.

Secondly, That whatever diminishes the quantity of oxygen, diminishes
the excitability.

The excitability of animals, made to breathe oxygen gas, or to take
the oxygenated muriate of potash, or acid fruits, is very much
increased.

On the contrary, when persons have inspired carbonic acid, or azotic
gas, or have taken into the system substances which have a strong
affinity for oxygen, and therefore tend to abstract it, such as
hydrogen, and spirits, the excitability becomes very much diminished.

When we sleep, in consequence of the excitability being exhausted,
the breathing becomes free, and a great quantity of oxygen is
received by the lungs, and combined with the blood, while very little
of it becomes exhausted by the actions of the body, for none,
excepting those which are called involuntary motions, are carried on
during sound sleep: so that in a few hours the body recovers the
excitability which it had lost: it is again sensible of the
impressions of external objects, and with the return of light we