.

The first observation which strikes us, is that of the very different
effects that are produced when inanimate bodies act on each other,
and when they exert their action on living matter.

When dead matter acts upon dead or inanimate matter, the only effects
we perceive are mechanical, or chemical; that is, either motion, or
the decomposition and new combination of their parts. If one ball
strikes another, it communicates to it a certain quantity of motion,
this is called mechanical action; and if a quantity of salt, or
sugar, be put into water, the particles of salt, or sugar, will
separate from each other, and join themselves to the particles of the
water; these substances in these instances are said to act chemically
on each other, and in all cases whatever, in which inanimate or dead
bodies act on each other, the effects produced are motion, or
chemical attraction; for though there may appear to be other species
of action which sometimes take place, such as electric and magnetic
attraction and repulsion, yet these are usually referred to the head
of mechanical action or attraction.

But when dead matter acts upon those bodies we call living, the
effects produced are much different. There are many animals which
pass the winter in a torpid state which has all the appearance of
death; and they would continue in that state, if deprived of the
influence of heat; now heat if applied to dead matter, will only
produce motion, or chemical combination: in fluids it produces
motions by occasioning a change in their specific gravity; and we
know that it is one of the most powerful agents in chemical
combination and decomposition; but these are the only effects it
produces when it acts upon dead matter. But let us examine its
effects when applied to living organized bodies. Bring a snake or
other torpid animal into a moderately warm room, and observe what
will be the consequence. After a short time the animal begins to
move, to open its eyes and mouth; and when it has been subject to the
action of heat for a longer time, it crawls about in search of food,
and performs all the functions of life.

Here then, dead matter, when applied to the living body, produces the
living functions, sense and motion: for if the heat had not been
applied, the animal would have continued senseless, and apparently
lifeless.

In more perfect animals, the effects produced by the action of dead
matter upon them, are more numerous, and are dif