wake.

These facts afford satisfactory proofs that the excitability of the
body is proportioned to the oxygen which it receives: but in what
manner it produces this state of susceptibility, and how it is
exhausted by stimulants, we have yet to learn.

The following theory may perhaps throw some light upon the subject. I
propose it, however, merely as an hypothesis, for we have no direct
proofs of it, but it seems to account for many phenomena.

It is now well known, that while the limb of an animal possesses
excitability, the smallest quantity of electricity sent along the
principal nerve leading to it, produces contractions similar to those
produced by the will. This is instanced in the common galvanic
experiment with the limb of a frog, which I had formerly occasion to
show.

From the effects produced, when a stream of electricity is sent
through water, I think it not improbable that hydrogen and
electricity may be identical. When a piece of zinc and silver are
connected together, and the zinc is put in a situation to decompose
water, and oxidate, a current of hydrogen gas will separate from the
silver wire, provided this be immersed under water; but when it is
not, a current of electricity passes, which is sensible to the
electrometer.

Now there appears no greater improbability in the supposition that
hydrogen, in a certain state, may be capable of passing through
metals, and animal substances, in the form of electricity, and that
when it comes in contact with water, which is not so good a
conductor, it may combine with caloric, and form hydrogen gas, in
which state it becomes incapable of passing through the conductors of
electricity: I say there appears no greater improbability in this,
than that caloric should sometimes be in such a state, that it will
pass through metals, and animal substances, which conduct it, and at
other times, as when combined with oxygen or hydrogen, it should form
gases, and be then incapable of passing through these conductors of
heat. Galvanic effects may be produced by the oxidation of fresh
muscular fibre without the aid of metals, and contractions have been
thus produced in the limb of an animal; and we have already noticed,
that when this contraction ceases, it may be restored, by moistening
the limb with oxygenated muriatic acid.

The excitability of the body may, most probably, be conveyed by
respiration, and the circulation of the blood, which tend continually
to oxidat