uscular power, and throws
the blood through a large vessel into the lungs, which are contiguous,
and through which it circulates by millions of small ramifications. Here
it comes in contact with the air which we breathe. The action of the air
on the blood in the lungs is, indeed, concealed, from our immediate
observation; but we are able to form a tolerably accurate judgment of it
from the changes which it effects not only in the blood, but also on the
air expired.

The air, after passing through the lungs, is found to contain all the
nitrogen inspired, but to have lost part of its oxygen, and to have
acquired a portion of watery vapour and of carbonic acid gas. Hence it
is inferred, that when the air comes in contact with the venous blood in
the lungs, the oxygen attracts from it the superabundant quantity of
carbon with which it has impregnated itself during the circulation, and
converts it into carbonic acid. This gaseous acid, together with the
redundant moisture from the lungs*, being then expired, the blood is
restored to its former purity, that is, to the state of arterial blood,
and is thus again enabled to perform its various functions.

[Footnote *: The quantity of moisture discharged by the lungs in
24 hours, may be computed at eight or nine ounces.]

CAROLINE.

This is truly wonderful! Of all that we have yet learned, I do not
recollect any thing that has appeared to me so curious and interesting.
I almost believe that I should like to study anatomy now, though I have
hitherto had so disgusting an idea of it. Pray, to whom are we indebted
for these beautiful discoveries?

MRS. B.

Priestley and Crawford, in this country, and Lavoisier, in France, are
the principal inventors of the theory of respiration. Of late years the
subject has been farther illustrated and simplified by the accurate
experiments of Messrs. Allen and Pepys. But the still more important and
more admirable discovery of the circulation of the blood was made long
before by our immortal countryman Harvey.

EMILY.

Indeed I never heard any thing that delighted me so much as this theory
of respiration. But I hope, Mrs. B., that you will enter a little more
into particulars before you dismiss so interesting a subject. We left
the blood in the lungs to undergo the salutary change: but how does it
thence spread to all the parts of the body?

MRS. B.

After circulating through the lungs, the blood is collected into four
large v