The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
John Stuart Mill · en
F F. The _great aorta_, the blood vessel which conveys arterial
blood from the heart, and gives off branches that supply every
part of the body.
G. Another large vein which returns the blood from the muscles of
the chest, &c.
H H. The _thoracic duct_, which receives the newly dissolved food
from the small absorbents, that collect it from the intestines. It
conveys this nutrition (called chyle) upward along the back, until
it reaches where the duct turns into the junction of two veins,
and pours its contents into the veins bringing blood back to the
heart. The nutrition, therefore, is at this moment mixed with the
venous blood, and is sent to the lungs to be oxygenised.
[Verse: "But now hath God set the members in the body, every one as
it pleased him."--1 CORINTHIANS XII.]
885. _How is the nutrition taken away from the bilious residue?_
The muscular threads (or hands, as we figuratively call them) continue
to push forward the digested matter through a long tube, called _the
alimentary canal_, or bowels. This canal is some thirty feet in length,
and is folded in various layers across the abdomen, and tied to the
edge of a sort of apron, which is gathered up and fastened to the
back-bone. All along this alimentary canal those muscular hands are
pushing the digested mass along. But upon the coat or surface of the
canal there are millions of little vessels called _lacteals_, which
look out for the minute globules of milk as they pass, and _absorb_
them, which means that they pick them up, and carry them away. There is
an immense number of these little vessels, all busily at work picking
up food for the system.
Then there is a large vessel, called the _thoracic duct_, which comes
down and communicates with those little vessels (it is a sort of
overseer, having a large number of workmen,) and collects the produce
of their toil, and carries it upwards to the part where it passes _from
the organs of digestion_ into the _vessels of circulation_.
886. _What becomes of the nutrition, when it has entered the vessels of
the circulation?_
It is sent through a large vein into _the heart_, entering that organ
on the right side, from which the heart propels it into the lungs,
mixed with _venous blood_; and the venous, or blue blood, is sent into
the lungs, _taking with it the milk_, the formation of which we have
traced.
887. _Why are the venous blood and the chyle sent to the lungs?_