( 274, )

dergoes a change, and passes into the veins, which bring it
by four trunks into the left auricle of the heart. It is pre-
vented returning from the pulmonary arteiy into the right
ventricle, by the three semilunar valves which are placed at
its origin. The blood having thus passed through the lungs,
and become of a florid colour, distends the left auricle, which
is then stimulated to contract, and pours the blood into the
left ventricle. The left ventricle next contracts, and propels
the blood through the aorta, to be crmveyed by its branches
to every part of the body. The mitral valves, which are
placed at the auricular opening into the left ventricle, prevent
the blood from returning, when the ventricle contracts, into
the auricle : and, should the blood be prevented by any im-
pediment passing immediately along the aorta, the three
semilunar valves placed at its origin prevent its regurgi-
tating into the ventricle. From the numerous arteries of
the aorta the blood is conveyed into the veins, where it
loses its florid colour, becomes darker, and is conveyed by
the two vena; cavoe, the superior and inferior, into the right
auricle.

Since the blood loses its florid hue as it passes from the
arteries into the veins, and again acquires it only in the longs,
it fellows that the blood of the right auricle and ventricle,
and also the pulmonary ai tery, is of a dark venal colour ; and
that of the pulmonary veins, left auricle and ventricle, and
aortal system, of a Jiorid hue.

The above circumstance naturally induces the following
observation : that when blood is expectorated of a florid
"hue, it comes from a ruptured vein; and when dark and
prumoiis, from the pulmonary artery. As the bron-
chial artery ramifies through the parenchyma of the
Inngs, when it ruptures, an eccbymosis of the lung is the
consequence.