i jo Circulation of the Blood 



observe correctly ; for, at the time the heart gathers 

 itself up, and becomes erect, it is certain that it is rather 

 lessened in every one of its dimensions ; that it is in its 

 systole, in short, not in its diastole. Neither, on the 

 contrary, when it collapses and sinks down, is it then 

 properly in its state of diastole and distension, by which 

 the ventricles become more capacious. But as we do 

 not say that the heart is in the state of diastole in the 

 dead body, as having sunk relaxed after the systole, 

 but is then collapsed, and without all motion in short 

 is in a state of rest, and not distended. It is only 

 truly distended, and in the proper state of diastole, 

 when it is filled by the charge of blood projected into 

 it by the contraction of the auricles ; a fact which 

 sufficiently appears in the course of vivisections. 

 Descartes therefore does not perceive how much the 

 relaxation and subsidence of the heart and arteries 

 differ from their distension or diastole ; and that the 

 cause of the distension, relaxation, and constriction, is 

 not one and the same ; as contrary effects so must they 

 rather acknowledge contrary causes ; as different move- 

 ments they must have different motors ; just as all 

 anatomists know that the flexion and extension of an 

 extremity are accomplished by opposite antagonist 

 muscles, and contrary or diverse motions are neces- 

 sarily performed by contrary and diverse organs 

 instituted by nature for the purpose. Neither do I 

 find the efficient cause of the pulse aptly explained by 

 this philosopher, when with Aristotle he assumes the 

 cause of the systole to be the same as that of the 

 diastole, viz. an effervescence of the blood due to a kind 

 of ebullition. For the pulse is a succession of sudden 

 strokes and quick percussions ; but we know of no kind 

 of fermentation or ebullition in which the matter rises 

 and falls in the twinkling of an eye ; the heaving is 

 always gradual where the subsidence is notable. 

 Besides, in the body of a living animal laid open, we 

 can with our eyes perceive the ventricles of the heart 



