veins. The pulmonary artery receives the blood from the right chamber of
the heart, and carries it to the minute extensive ramifications of the
lungs, where it is exposed to the action of the air on a surface equal to
that of the whole external skin, through the thin moist coats of those
vessels, which are spread on the air-cells, which constitute the minute
terminal ramifications of the wind-pipe. Here the blood changes its colour
from a dark red to a bright scarlet. It is then collected by the branches
of the pulmonary vein, and conveyed to the left chamber of the heart.

6. The aorta is another large artery, which receives the blood from the
left chamber of the heart, after it has been thus aerated in the lungs, and
conveys it by ascending and descending branches to every other part of the
system; the extremities of this artery terminate either in glands, as the
salivary glands, lacrymal glands, &c. or in capillary vessels, which are
probably less involuted glands; in these some fluid, as saliva, tears,
perspiration, are separated from the blood; and the remainder of the blood
is absorbed or drank up by branches of veins correspondent to the branches
of the artery; which are furnished with valves to prevent its return; and
is thus carried back, after having again changed its colour to a dark red,
to the right chamber of the heart. The circulation of the blood in the
liver differs from this general system; for the veins which drink up the
refluent blood from those arteries, which are spread on the bowels and
mesentery, unite into a trunk in the liver, and form a kind of artery,
which is branched into the whole substance of the liver, and is called the
vena portarum; and from which the bile is separated by the numerous hepatic
glands, which constitute that viscus.

7. The glands may be divided into three systems, the convoluted glands,
such as those above described, which separate bile, tears, saliva, &c.
Secondly, the glands without convolution, as the capillary vessels, which