16 ON THE HEART AND BLOOD. 



any obstacle to its passage from the mitral valves, when they 

 have previously asserted that the air entered by the same vessel 

 from the lungs into the left ventricle, and have brought forward 

 these same mitral valves as obstacles to its retrogression? Good 

 God ! how should the mitral valves prevent regurgitation of air 

 and not of blood ? 



Further, when they dedicate the vena arteriosa (or pulmonary 

 artery), a vessel of great size, and having the tunics of an artery, 

 to none but a kind of private and single purpose, that, namely, 

 of nourishing the lungs, why should the arteria venalis (or 

 pulmonary vein), which is scarcely of similar size, which has 

 the coats of a vein, and is soft and lax, be presumed to be made 

 for many three or four, different uses ? For they will have it 

 that air passes through this vessel from the lungs into the left 

 ventricle ; that fuliginous vapours escape by it from the heart 

 into the lungs ; and that a portion of the spirituous or spiritual- 

 ized blood is distributed by it to the lungs for their refreshment. 



If they will have it that fumes and air fumes flowing from, 

 air proceeding towards the heart are transmitted by the same 

 conduit, I reply, that nature is not wont to institute but one 

 vessel, to contrive but one way for such contrary motions and 

 purposes, nor is anything of the kind seen elsewhere. 



If fumes or fuliginous vapours and air permeate this vessel, 

 as they do the pulmonary bronchia, wherefore do we find neither 

 air nor fuliginous vapours when we divide the arteria venosa ? 

 why do we always find this vessel full of sluggish blood, never 

 of air ? whilst in the lungs we find abundance of air remaining. 



If any one will perform Galen's experiment of dividing the 

 trachea of a living dog, forcibly distending the lungs with a 

 pair of bellows, and then tying the trachea securely, he will find, 

 when he has laid open the thorax, abundance of air in the lungs, 

 even to their extreme investing tunic, but none in either the pul- 

 monary veins, or left ventricle of the heart. But did the heart 

 either attract air from the lungs, or did the lungs transmit any 

 air to the heart, in the living dog, by so much the more ought 

 this to be the case in the experiment just referred to. Who, 

 indeed, doubts that, did he inflate the lungs of a subject in the 

 dissecting-room, he would instantly see the air making its way 

 by this route, were there actually any such passage for it ? But 

 this office of the pulmonary veins, namely, the transference of 

 air from the lungs to the heart, is held of such importance, that 



