te and form the hepatic vein,
which pours the blood into the vena cava, to be conducted to the
heart.

The reason of this deviation, is probably, to diminish the velocity
of the blood in the liver, for the secretion of the bile; which could
not have been effected by means of an artery.

The force which impels the blood, is, first, the contraction of the
heart, which propels the blood into the arteries with great velocity;
but this is not the only force concerned in keeping up the
circulation; this is evident, from the diminished heat, and weakened
pulse, in a paralytic limb, which ought not to take place, if the
blood were propelled merely by the action of the heart.

The arteries are possessed of an elastic and muscular power, by means
of which they contract when they are distended or stimulated. It is
however by the muscular power alone, that they assist in propelling
the blood; for the elasticity of their coats can serve no other
purpose than preserving the mean diameter of the vessel. If we
suppose the arteries to be dilated by the blood, poured into them by
the heart, they will, by their contraction, as elastic tubes,
undoubtedly propel the blood: but supposing them to be perfectly
elastic, the force of the heart will be just as much diminished in
dilating them as the force of the blood is increased by their
contraction. We are not however acquainted with any substance
perfectly elastic, or which restores itself with a force equal to
that with which it was distended: hence the elastic power of the
arteries will subtract from, instead of adding to, the power of the
heart. It is evident, therefore, that it must be by the muscular
power of the arteries, which causes them to contract like the heart,
that they propel the blood.

That such is the case, appears from the muscular structure of the
arteries observed by anatomists; as also from the effects of
mechanical irritation of their coats, which causes them to contract;
this is likewise evident from the inflammation produced by the
application of stimulating substances to particular parts; for
instance, cantharides and mustard. It appears likewise, from the
secretion in some parts being preternaturally increased, while the
motion of the general mass of the blood continues unaltered.

The contraction of the arteries always propels the blood towards the
extreme parts of the body: this must necessarily happen, because the
valves at the origin of the arteries preven