INTRODUCTION. 17 



Hieronymus Fabricius, of Aquapendente, maintains 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 wherefore, if the pulmo- 

 nary vein were destined for the conveyance of air, it has the 

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

 annular tubes, such as those of the bronchia, in order that they 

 might always remain open, not have been liable to collapse ; and 

 that they might continue entirely free from blood, lest the 

 liquid should interfere with the passage of the air, as it so ob- 

 viously does when the lungs labour from being either greatly 

 oppressed or loaded in a less degree with phlegm, as they are 

 when the breathing is performed with a sibilous or rattling noise. 



Still less is that opinion to be tolerated which (as a two-fold 

 matter, one aereal, one sanguineous, is required for the compo- 

 sition of vital spirits,) supposes the blood to ooze through the 

 septum of the heart from the right to the left ventricle by certain 

 secret pores, and the air to be attracted from the lungs through 

 the great vessel, the pulmonary vein; and which will have it, 

 consequently, that there are numerous pores in the septum cordis 

 adapted for the transmission of the blood. But, in faith, no such 

 pores can be demonstrated, neither in fact do any such exist. For 

 the septum of the heart is of a denser and more compact struc- 

 ture than any portion of the body, except the bones and sinews. 

 But even supposing that there were foramina or pores in this 

 situation, how could one of the ventricles extract anything 

 from the other the left, e. g. obtain blood from the right, when 

 we see that both ventricles contract and dilate simultane- 

 ously ? Wherefore should we not rather believe that the right 

 took spirits from the left, than that the left obtained blood from 

 the right ventricle, through these foramina ? But it is certainly 

 mysterious and incongruous that blood should be supposed to 

 be most commodiously drawn through a set of obscure or in- 

 visible pores, and air through perfectly open passages, at one 

 and the same moment. And why, I ask, is recourse had to 

 secret and invisible porosities, to uncertain and obscure chan- 

 nels, to explain the passage of the blood into the left ven- 

 tricle, when there is so open a way through the pulmonary veins? 

 I own it has always appeared extraordinary to me that they 

 should have chosen to make, or rather to imagine, a way through 



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