48 MOTION OF THE 



CHAPTER IX. 



THAT THERE IS A CIRCULATION OF THE BLOOD IS CONFIRMED 

 FROM THE FIRST PROPOSITION. 



BUT lest any one 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 wise that the whole mass 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 inces- 

 sant 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 man- 

 ner return this blood incessantly to the heart from all 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 extre- 

 mities to the heart, and thus that it performs a kind of circular 

 motion. 



Let us assume either arbitrarily or from experiment, the quan- 

 tity of blood which the left ventricle of the heart will contain 

 when distended to be, say two ounces, three ounces, one ounce 

 and a half in 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, and obvious from the structure of the valves ; 

 and let us suppose as approaching the truth that the fourth, 

 or fifth, or sixth, or even but the eighth part of its charge is 

 thrown into the artery at each contraction ; this would give either 

 half an ounce, or three drachms, or one drachm of blood as 



