100 CIRCULATION OF THE BLOOD. 



lation, the lungs are most readily depleted by opening a vein ; 

 but rejecting it, 1 do not see how any revulsion of the blood 

 can be accomplished by this means ; for did it flow back by the 

 pulmonary artery upon the right ventricle, the sigmoid valves 

 would oppose its entrance, and any escape from the right ven- 

 tricle into the vena cava is prevented by the tricuspid valves. 

 The blood, therefore, is soon exhausted when a vein is opened 

 in the arm or foot, if we admit the circulation; and the opinion 

 of Fernelius is at the same time upset by this admission, viz. 

 that in affections of the lungs it is better to bleed from the 

 right than the left arm; because the blood cannot flow back- 

 wards into the vena cava unless the two barriers situated in 

 the heart be first broken down." 



He adds yet further in the same place : 2 " If the circulation 

 of the blood be admitted, and it be acknowledged that this fluid 

 generally passes through the lungs, not through the middle par- 

 tition of the heart, a double circulation becomes requisite; one 

 effected through the lungs, in the course of which the blood 

 quitting the right ventricle of the heart passes through the 

 lungs in order that it may arrive at the left ventricle; leaving 

 the heart on the one hand, therefore, the blood speedily returns 

 to it again; another and longer circulation proceeding from the 

 left ventricle of the heart performs the circuit of the whole body 

 by the arteries, and by the veins returns to the right side of 

 the heart." 



The learned anatomist might here have added a third and 

 extremely short circulation, viz. from the left to the right 

 ventricle of the heart, with that blood which courses through 

 the coronary arteries and veins, and by their ramifications is 

 distributed to the body, walls, and septum of the heart. 



" He who admits one circulation," proceeds our author, "can- 

 not repudiate the other;" and he might, as it appears, have 

 added, " the third." For why should the coronary arteries of 

 the heart pulsate, if it were not to force on the blood by their 

 pulsations ? and why should there be coronary veins, the end 

 and office of all veins being to receive the blood brought by the 

 arteries, were it not to deliver and discharge the blood sent 

 into the substance of the heart ? In this consideration let it 



Lib. iii, cap. 6. 



