SECT. IV.
Of the Circulation of the Blood.
We shall now consider the circulation of the blood; the grand source of our existence. At the contemplation of which we must be lost in admiration, at the wonderful wisdom of its contrivance; and with uplifted eyes adore the cause of its motion!
The Heart, as I before observed, has two chambers or ventricles, distinguished by the right and left; each of these chambers have also a valvular cavity call’d auricle, or ear. Each ventricle opens itself into an artery and auricle; and each auricle opens itself into a ventricle and vein. These openings have valves, which open and shut alternately, and by this, prevent any confusion or hindrance in the influx and efflux of the blood.
The right ventricle is the longest and greatest, but weakest: From this ventricle springs forth the pulmonary artery, which spreads itself throughout the Lungs.
The right auricle is also the largest; in which opens itself the large vein, called vena cava; as the common trunk that receives the blood from all its branches spread over the whole human body.
The left ventricle is shorter, but the walls are considerably stronger than that of the right ventricle. Here begins the aorta, or the great artery, by which the blood is sent to all the parts of the human body.
The left auricle is also somewhat smaller than the right; and in that opens itself the pulmonary vein, which returns the blood from the lungs, after it has received its necessary assistance from the vesicles of air in the lungs.
This premised and understood, the circulation is performed in the following manner:
The right ventricle being full of blood, contracts itself. This contraction is called the systole, by which it forces the blood through the pulmonary artery into every part of the lungs, even into every vesicle; where it receives a portion of the air, drawn in by the wind-pipe.