oth in a few minutes fell into a
profound sleep, and after five minutes Sir Joseph Banks happily
succeeded in waking Dr. Solander, who had almost lost the use of his
limbs; the muscles were so shrunk, that his shoes fell from his feet;
but every attempt to recal the unfortunate black to life proved
unsuccessful.

As the circulation of the blood is the means by which the heat
produced is conveyed to all parts of the body; and as it is a
function of the highest importance, I shall, in the next lecture,
proceed to the consideration of it.

LECTURE III.
CIRCULATION OF THE BLOOD.

Two kinds of motion may be distinguished in the animal economy; the
one voluntary, or under the command of the will, which takes place at
certain intervals, but may be stopped at pleasure. The other kind of
motion is called involuntary, as not depending on the will, but going
on constantly, without interruption, both when we sleep and when we
wake.

Of the first kind is the motion of the limbs, of which I have already
spoken in general terms; the object of which is, to change the
situation of the animal, and carry it where the will directs.

Among the involuntary motions, the most remarkable is the circulation
of the blood, which I shall proceed to consider in this lecture.

There is one motion, however, which claims a middle place between the
voluntary and involuntary; I mean respiration. This action is so far
under the command of the will, that it may be suspended, increased,
or diminished in strength and frequency: but we can only suspend it
for a very short time; and it goes on regularly during sleep, and in
general, even when we are awake, without the intervention of the
will; its continuation being always necessary, as we have already
seen, to support life.

The motion of the fluids in the living body is regulated by very
different laws, from those which govern the motion of ordinary
fluids, that depend upon their gravity and fluidity: these last have
a general centre of gravitation to which they incessantly tend. Their
motion is from above downwards, when not prevented by any obstacles;
and when they meet with obstruction, they either stop till the
obstacle is removed, or escape where they find the least resistance.
When they have reached the lowest situations, they remain at rest,
unless acted upon by some internal impulse, which again puts them in
motion.

But the motion of the fluids in an animal body, is less uniform,
consta