Introduction 19 



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 obviously 

 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 

 twofold matter, one ae'real, one sanguineous, is required 

 for the composition 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, conse- 

 quently, 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 structure 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 simultaneously ? 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 

 invisible 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 channels, to explain the passage 

 of the blood into the left ventricle, when there is so 



