"Since I see that many are embarrassed and doubt the circulation, and that some attack it, because they have not understood me thoroughly; for their sake I will recapitulate briefly what I meant to say in my little book on the motion of the heart and blood. The blood contained in the veins, where its deeps are, as it were, where it is most abundant, that is, in the vena cava close to the base of the heart and to the right auricle, gradually grows warm and thin by reason of its own internal heat, and swells and rises up like matters in fermentation; whereby the auricle is dilated, contracts itself by reason of its own pulsific faculty, and propels the blood promptly and frequently into the right ventricle of the heart. This, when filled, frees itself of blood at its succeeding systole by the impulsion thereof and, as the tricuspid valve is a bar to the egress of the blood, drives it where an open door is offered, into the arterial vein, and thereby brings about the expansion of the latter. The blood within the arterial vessels cannot now go back in opposition to the sigmoid valve, while at the same time the lungs are widened and enlarged and then narrowed by inspiration and expiration--and with the lungs their vessels also--and offer to the blood aforesaid a path and transit into the venous artery. The left auricle accomplishes its movement, its rhythm, its order [of events], its function, at the same time and in the same way as the right auricle, and in like manner sends on into the left ventricle out of the vessels aforesaid the same blood which the right auricle had sent on into the right ventricle. As a result the left ventricle, at the same time and in the same way as the right, impels the blood into the cavity of the aorta and consequently into all the branches of the artery, the return of the blood whence it had come being prevented in the same way as before by the barrier of an opposing valve. The arteries are filled by this sudden impulsion and, as they cannot unload themselves as suddenly, are expanded, receive an impulse, and undergo their diastole."[230]