INTRODUCTION 75 



Moreover, when they appoint the pulmonary artery, a vessel 

 of great size, with the coverings of an artery, to none but a 

 kind of private and single purpose, that, namely, of nourishing 

 the lungs, why should the pulmonary vein, which is scarcely 

 so large, 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 blood is distributed 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 construct 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 pulmonary vein? 

 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 

 pulmonary veins or the 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, much 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 trans- 

 ference of air from the lungs of the heart, is held of such im- 

 portance, that Hieronymus Fabricius of Aquapendente, con- 

 tends that the lungs were made for the sake of this vessel, and 

 that it constitutes the principal element in their structure. 



But I should like to be informed why, if the pulmonary vein 

 were destined for the conveyance of air, it has the structure 

 of a blood-vessel here. Nature had rather need of annular 



