therefore, naturally
concerns us all. In this lecture, I shall not attempt to teach you
to become your own physicians, for when the barriers of health are
once broken down, and disease has established itself, it requires
the deepest attention, and an accurate acquaintance with the
extensive science of medicine, to combat it; to attain this
knowledge demands the labour of years. But, a majority of the
diseases to which we are subject, are the effects of our own
ignorance or imprudence, and it is often very easy to prevent them;
mere precepts however, have seldom much effect, unless the reasoning
upon them be rendered evident; on this account, I shall first
endeavour, in as plain and easy a manner as possible, to explain to
you the laws by which life is governed; and when we see in what
health consists, we shall be better enabled to take such methods as
may preserve it. Health is the easy and pleasant exercise of all the
functions of the body and mind; and disease consists in the uneasy
and disproportioned exercise of all, or some of the functions.

When dead matter acts upon dead matter, the only effects we perceive
are mechanical, or chemical; for though there may appear to be other
kinds of attraction, or repulsion, such as electric and magnetic,
yet these come under the head of mechanical attraction, as producing
motion; we may therefore lay it down as a law, that when dead, or
inanimate bodies act upon each other, no other than mechanical, or
chemical effects are produced; that is, either motion, or the
decomposition, and new combination of their parts. If one ball
strike 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 the salt or sugar will
separate from each other, and join themselves to the particles of
the water; the salt and water in these instances, are said to act on
each other chemically; and in all cases whatever, in which
inanimate, or dead bodies act on each other, the effects produced
are, motion, or chemical attraction.

But, when dead matter acts on those bodies which we call living, the
effects are much different; let us take for example a very simple
instance.--Snakes, at least some species of them, pass the winter in
a torpid state, which has all the appearance of death; now heat, if
applied to dead matter, will only produce motion, or chemical
combination; but if it be applied t