alth,
seldom known to any but savages, and brute animals not under the
dominion of man, who regulate these powers merely by the necessities
of nature.

When air is applied in too great quantity, and especially if some of
the tubes convey oxygen gas, then a violent combustion and flame is
excited, which will, in all probability, consume or burn out the
furnace or grate, or if it do not, it will burn out the fuel, and
thus exhaust itself.

In like manner, if the stimulants which support life be made to act
too powerfully, and particularly if any powerful stimulus, not
natural to the body, such as wine or spirits, be taken in too great
quantity, a violent inflammatory action will be the consequence,
which may destroy the human machine: but if it do not, it will
exhaust the excitability, and thus bring on great debility.

This analogy might be pursued further, but my intention was solely to
illustrate some of the outlines of our theory, by a comparison which
may facilitate the conception of the manner in which external powers
act on living bodies. The different powers which support life, and
without whose action we are unable to exist, such as heat, food, air,
&c. have been very improperly called nonnaturals, a term which is
much more applicable to those substances which we are daily in the
habit of receiving into the system, which excite it to undue actions,
and which nature never intended we should receive; such as spirituous
and fermented liquors, and high seasoned foods. In the preceding
illustration, I have spoken of a tube, as constantly pouring in fresh
fuel, because it was not easy otherwise to convey a familiar idea of
the power which all living systems possess of renewing their
excitability, when exhausted. The excitability is an unknown
somewhat, subject to peculiar laws, some of which we have examined,
but whose different states we are obliged to describe, though,
perhaps, inaccurately, by terms borrowed from the qualities of
material substances.

Though Dr. Brown very properly declined entering into the
consideration of the nature of excitability, or the manner in which
it is produced, the discoveries which have been made in chemistry
since his time, have thrown great light on the subject, and it is now
rendered highly probable that the excitability or vital principle, is
communicated to the body by the circulation, and is intimately
connected with the process of oxidation.

Many circumstances would ten