marked only in the neighborhood of the heart; and is not so evident in
parts more remote from it. In the next place, the consistency of the coats
of which the arterial vein and the great artery are composed,
sufficiently shows that the blood is impelled against them with more
force than against the veins. And why should the left cavity of the heart
and the great artery be wider and larger than the right cavity and the
arterial vein, were it not that the blood of the venous artery, having
only been in the lungs after it has passed through the heart, is thinner,
and rarefies more readily, and in a higher degree, than the blood which
proceeds immediately from the hollow vein? And what can physicians
conjecture from feeling the pulse unless they know that according as the
blood changes its nature it can be rarefied by the warmth of the heart, in
a higher or lower degree, and more or less quickly than before? And if it
be inquired how this heat is communicated to the other members, must it
not be admitted that this is effected by means of the blood, which,
passing through the heart, is there heated anew, and thence diffused over
all the body? Whence it happens, that if the blood be withdrawn from any
part, the heat is likewise withdrawn by the same means; and although the
heart were as-hot as glowing iron, it would not be capable of warming the
feet and hands as at present, unless it continually sent thither new
blood. We likewise perceive from this, that the true use of respiration is
to bring sufficient fresh air into the lungs, to cause the blood which
flows into them from the right ventricle of the heart, where it has been
rarefied and, as it were, changed into vapors, to become thick, and to
convert it anew into blood, before it flows into the left cavity, without
which process it would be unfit for the nourishment of the fire that is
there. This receives confirmation from the circumstance, that it is
observed of animals destitute of lungs that they have also but one cavity
in the heart, and that in children who cannot use them while in the womb,
there is a hole through which the blood flows from the hollow vein into