44 MOTION OF THE 



can use it with still greater propriety, merely changing the terms, 

 for the passage of the blood from the veins through the heart 

 into the arteries. From Galen, however, that great man, that 

 father of physicians, it clearly appears that the blood passes 

 through the lungs from the pulmonary artery into the minute 

 branches of the pulmonary veins, urged to this both by the 

 pulses of the heart and by the motions of the lungs and thorax ; 

 that the heart, moreover, is incessantly receiving and expelling 

 the blood by and from its ventricles, as from a magazine or 

 cistern, and for this end is furnished with four sets of valves, 

 two serving for the induction and two for the eduction of the 

 blood, lest, like the Euripus, it should be incommodiously sent 

 hither and thither, or flow back into the cavity which it should 

 have quitted, or quit the part where its presence was required, 

 and so the heart be oppressed with labour in vain, and the office 

 of the lungs be interfered with. 1 Finally, our position that the 

 blood is continually passing from the right to the left ventricle, 

 from the vena cava into the aorta, through the porous structure 

 of the lungs, plainly appears from this, that since the blood is 

 incessantly sent from the right ventricle into the lungs by the 

 pulmonary artery, and in like manner is incessantly drawn from 

 the lungs into the left ventricle, as appears from what precedes 

 and the position of the valves, it cannot do otherwise than 

 pass through continuously. And then, as the blood is inces- 

 santly flowing into the right ventricle of the heart, and is con- 

 tinually passed out from the left, as appears in like manner, and 

 as is obvious both to sense and reason, it is impossible that the 

 blood can do otherwise than pass continually from the vena cava 

 into the aorta. 



Dissection consequently shows distinctly what takes place [in 

 regard to the transit of the blood] in the greater number of 

 animals, and indeed in all, up to the period of their [foetal] 

 maturity ; and that the same thing occurs in adults is equally 

 certain, both from Galen's words, and what has already been 

 said on the subject, only that in the former the transit is 

 effected by open and obvious passages, in the latter by the 

 obscure porosities of the lungs and the minute inoscula- 



1 See the Commentary of the learned Hofmann upon the Sixth Book of Galen, 

 ' De Usu partium,' a work which I first saw after I had written what precedes. 



