njurious to it.

We shall afterwards see, that the nerves are not only instruments
of sensation, but the origin of motion; it being immediately by
their means that the muscles are moved. A certain degree of heat
is necessary to keep the blood fluid, and also to the action of
the nerves; without either of which, no motion could be performed.
Respiration or breathing is so necessary to life, that it cannot
exist, even a few minutes, without the exercise of that function;
and yet we shall afterwards see, that the ultimate end of
respiration is to keep the body in a proper state, for the
purposes of muscular motion and sensation.

The skin serves like a sheath to defend the body from injuries;
the skull serves the same purpose to the brain, which is the
origin of the nerves. The different membranes separate the fibres,
muscles, nerves, and various organs of the body, from each other.
Hence we see that there is no impropriety, in calling the human
body a machine composed of bones and muscles, with their proper
appendages, for the purpose of motion, at the instance of its
intelligent principle.

In order to show more clearly how each part is subservient to
these ends, I shall give a short account of the structure of the
human body, but I must premise, that the nature of this course
will prevent my entering minutely into anatomical detail. All that
can be done is, to give such a general outline of anatomy and
physiology, as will furnish individuals with so much knowledge of
themselves, as may enable them to guard against habitual sickness.

Among the solid parts of the human frame the bones stand
conspicuous. Their use is, to give firmness and shape to the body.
Some of them likewise serve as armour, or defense, to guard
important parts; thus the skull is admirably contrived to defend
the brain; and the spine or backbone is designed, not only to
strengthen the body, but to shield that continuation of the brain,
called the spinal marrow, from whence originate great numbers of
nerves, which pass through convenient openings of this bone, and
are distributed to various parts of the body. In the structure of
this, as well as every other part, the wisdom of the Creator is
manifest. Had it been a single bone, the loins must have been
inflexible; to avoid which, it consists of a number of small
bones, articulated or joined together with great exactness, which
are strengthened by compact ligaments. Hence it becomes capable of
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