through the lungs, becomes combined with oxygen; that this oxidated
blood, on its return to the heart, is circulated by the arteries to
all parts of the body; and that, during this circulation, its oxygen
combines with the hydrogen and carbon of the blood, and perhaps with
those parts of the body with which it comes into contact; it is
therefore brought back to the heart, by the veins, of a dark colour,
and deprived of the greatest part of its oxygen.

This is the most probable theory, in the present state of our
knowledge; it was proposed by Lavoisier, who imagines the focus of
heat, or fireplace to warm the body, to be in the lungs: others,
however, have thought it more consonant to facts, to suppose, that,
instead of the oxygen uniting with carbon and hydrogen in the lungs,
and there giving out its heat, the oxygen is absorbed by the blood,
and unites with these substances during the circulation, so that heat
is produced in every part of the body; and this doctrine seems
certainly supported by several facts and experiments.

The circulation of the blood, though so simple and beautiful a
function, was unknown to the ancient physicians, and was first
demonstrated by our countryman, Harvey; when he first published his
account of this discovery, he met with the treatment which is
generally experienced by those who enlighten and improve the comfort
of their fellow creatures, by valuable discoveries. The novelty and
merit of this discovery drew upon him the envy of most of his
contemporaries in Europe, who accordingly opposed him with all their
power; and some universities even went so far, as to refuse the
honours of medicine to those students, who had the audacity to defend
this doctrine; but afterwards, when they could not argue against
truth and conviction, they attempted to rob him of the discovery, and
asserted that many of the ancient physicians, and particularly
Hippocrates, were acquainted with it. Posterity, however, who can
alone review subjects of controversy without prejudice, have done
ample justice to his memory.

LECTURE IV.
DIGESTION, NUTRITION, &c.

The human body, by the various actions to which it is subject, and
the various functions which it performs, becomes, in a short time,
exhausted; the fluids become dissipated, the solids wasted, while
both are continually tending towards putrefaction. Notwithstanding
which, the body still continues to perform its proper functions,
often for a considerabl