e the different parts: and hydrogen or electricity may be
secreted by the brain, and sent along the nerves, which are such good
conductors of it, and by uniting with the oxygen of the muscle, may
cause it to contract; but as the oxygen will, by this union, be
diminished, if the contractions be often repeated, the excitability
will thus be expended faster than it can be supplied by the
circulation, and will become exhausted. But will facts bear us out in
this explanation? To see this, we must examine the chemical nature of
the substances which produce the greatest action, and the greatest
exhaustion of the vital principle: namely, those which produce
intoxication.

Fermented liquors differ from water, in containing carbon and more
hydrogen: these produce intoxication: but pure spirits, which contain
still more hydrogen, produce a still higher degree of intoxication,
and consequent exhaustion of the excitability. Ether, which appears
to be little more than condensed hydrogen, probably kept in a liquid
state by union with a small quantity of carbon, and which easily
expands by caloric into a gas, which very much resembles hydrogen
gas, produces a still greater degree of intoxication: so that we see
the action produced by different substances, as well as the
exhaustion of excitability which follows, is proportioned to the
quantity of hydrogen they contain.

There is another circumstance which seems to strengthen this idea.
The intoxicating powers of spirits are diminished by the addition of
vegetable acids, or substances which contain oxygen, which will
counteract the effects of the hydrogen. Thus it is known that the
same quantity of spirit, made into punch, will not produce either the
same ebriety, or the same subsequent exhaustion, as when simply mixed
with water.

Recollect however that I propose this only as a hypothesis: its truth
may be confirmed by future observations and experiments, or it may be
refuted by them: but it is certainly capable of explaining many of
the phenomena, which is one of the conditions required by Newton's
first rule of philosophizing.

Heat, and light, and other stimuli, may perhaps exhaust the
excitability, by facilitating the combination of oxygen in the fibres
with the hydrogen and carbon in the blood.

There are several substances which cause a diminution or exhaustion
of the excitability, without producing any previous increased
excitement. These substances have by physicians been