Harvey
CHAPTER
IX THAT
THERE IS A CIRCULATION OF THE BLOOD But lest anyone should
say that we give them words only, and make mere specious assertions
without any foundation, and desire to innovate without sufficient cause,
three points present themselves for confirmation, which being stated, I
conceive that the truth I contend for will follow necessarily, and appear
as a thing obvious to all. First,-the blood is incessantly transmitted by
the action of the heart from the vena cava to the arteries in such
quantity that it cannot be supplied from the ingesta, and in such a manner
that the whole must very quickly pass through the organ; Second, 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; Third,—the veins in like
manner return this blood incessantly to the heart from parts and members
of the body. These points proved, I conceive it will be manifest that the
blood circulates, revolves, propelled and then returning, from the heart
to the extremities, from the extremities to the heart, and thus that it
performs a kind of circular motion. Let us assume either arbitrarily or from experiment, the quantity of blood which the left ventricle of the heart will contain when distended, to be, say two ounces, three ounces, or one ounce and a half-ill the dead body I have found it to hold upwards of two ounces. Let us assume further, how much less the heart will hold in the contracted than in the dilated state; and how much blood it will project into the aorta upon each contraction;-and all the world allows that with the systole something is always projected, a necessary consequence demonstrated in the third chapter.
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