William Harvey's
On the Motion of the Heart and Blood in Animals.
Upon closer examination and after much thought on the anatomy
of the different structures of the circulatory system and the volume
of blood circulating, Harvey began to formulate another idea:
I began to think whether there might not be a MOTION, AS IT WERE, IN A CIRCLE. Now, this I afterwards found to be true; and I finally saw that the blood, forced by the action of the left ventricle into the arteries, was distributed to the body at large, and its several parts, in the same manner as it is sent through the lungs, impelled by the right ventricle into the pulmonary artery, and that it then passed through the veins and along the vena cava, and so round to the left ventricle in the manner already indicated.
Harvey then speculates on the purpose of this circular motion
of the blood:
And similarly does it come to pass in the body,
through the motion of the blood, that the various parts are nourished,
cherished, quickened by the warmer, more perfect, vaporous, spirituous,
and, as I may say, alimentive blood; which, on the other hand, owing
to its contact with these parts, becomes cooled, coagulated, and so
to speak effete. It then returns to its sovereign, the heart, as if
to its source, or to the inmost home of the body, there to recover its
state of excellence or perfection. Here it renews its fluidity, natural
heat, and becomes powerful, fervid, a kind of treasury of life, and
impregnated with spirits, it might be said with balsam. Thence it is
again dispersed. All this depends on the motion and action of the heart.
The heart, consequently, is the beginning of life; the sun of the microcosm,
even as the sun in his turn might well be designated the heart of the
world; for it is the heart by whose virtue and pulse the blood is moved,
perfected, and made nutrient, and is preserved from corruption and coagulation;
it is the household divinity which, discharging its function, nourishes,
cherishes, quickens the whole body, and is indeed the foundation of
life, the source of all action.