mpelled 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;

(3) The veins in like manner return this blood incessantly to the heart
from all parts and members of the body.

As to the first proposition Harvey says, "Did the heart eject but two
drachms of blood on each contraction, and the beats in half an hour were
a thousand, the quantity expelled in that time would amount to twenty
pounds and ten ounces; and were the quantity an ounce, it would be as
much as eighty pounds and four ounces. Such quantities, it is certain,
could not be supplied by any possible amount of meat and drink consumed
within the time specified. It is the same blood, consequently, that is
now flowing out by the arteries, now returning by the veins; and it is
simply matter of necessity that the blood should perform a circuit, or
return to the place from whence it went forth."

Demonstration of the second proposition--that the blood enters a limb by
the arteries and returns from it by the veins--is afforded by the
effects of a ligature. For if the upper part of the arm be _tightly_
bound, the arteries below will not pulsate, while those above will throb
violently. The hand under such circumstances will retain its natural
colour and appearance, although, if the bandage be kept on for a minute
or two, it will begin to look livid and to fall in temperature. But if
the bandage be now slackened a little, the hand and the arm will
immediately become suffused, and the superficial veins show themselves
tumid and knotted, the pulse at the wrist in the same instant beginning
to beat as it did before the application of the bandage. The tight
bandage not only compresses the veins, but the arteries also, so that
blood cannot flow through either. The slacker ligature obstructs the
veins only, for the arteries lie deeper and have firmer coats. "Seeing,
then," says Harvey, "that the moderately tight ligature renders the
veins turgid, and the whole hand full of blood, I ask, Whence is this?
Does the blood accumulate below the ligature coming through the veins,
or through the arteries, or passing by certain secret pores? Through the
veins it cannot come; still less can it come by any system of invisible
pores; it must needs, then, arrive by the arteries."

The third position to be proved is t