nsider what
happens in the dissection of living animals. The great artery need not
be divided, but a very small branch only (as Galen even proves in regard
to man), to have the whole of the blood in the body, as well that of the
veins as of the arteries, drained away in the course of no long
time--some half hour or less.

The second point is this. The blood, under the influence of the arterial
pulse, enters, and is impelled in a continuous, equable, and incessant
stream through every part and member of the body in much larger quantity
than were sufficient for nutrition, or than the whole mass of fluids
could supply.

I have here to cite certain experiments. Ligatures are either very tight
or of middling tightness. A ligature I designate as tight, or perfect,
when it is drawn so close about an extremity that no vessel can be felt
pulsating beyond it. Such ligatures are employed in the removal of
tumours; and in these cases, all afflux of nutriment and heat being
prevented by the ligature, we see the tumours dwindle and die, and
finally drop off. Now let anyone make an experiment upon the arm of a
man, either using such a fillet as is employed in bloodletting, or
grasping the limb tightly with his hand; let a ligature be thrown about
the extremity and drawn as tightly as can be borne. It will first be
perceived that beyond the ligature the arteries do not pulsate, while
above it the artery begins to rise higher at each diastole and to swell
with a kind of tide as it strove to break through and overcome the
obstacle to its current.

Then let the ligature be brought to that state of middling tightness
which is used in bleeding, and it will be seen that the hand and arm
will instantly become deeply suffused and extended, and the veins show
themselves tumid and knotted. Which is as much as to say that when the
arteries pulsate the blood is flowing through them, but where they do
not pulsate they cease from transmitting anything. The veins again being
compressed, nothing can flow through them; the certain indication of
which is that below the ligature they are much more tumid than above it.

Whence is this blood? It must needs arrive by the arteries. For that it
cannot flow in by the veins appears from the fact that the blood cannot
be forced towards the heart unless the ligature be removed. Further,
when we see the veins below the ligature instantly swell up and become
gorged when from extreme tightness it is somewhat rel