140 CIRCULATION OF THE BLOOD. 



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 subsi- 

 dence 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 

 movements they must have different motors ; just as all ana- 

 tomists know that the flexion and extension of an extremity 

 are accomplished by opposite antagonist muscles, and contrary 

 or diverse motions are necessarily 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 per- 

 ceive the ventricles of the heart both charged and distended 

 by the contraction of the auricles, and more or less increased 

 in size according to the charge ; and farther, we can see that 

 the distension of the heart is rather a violent motion, the effect 

 of an impulsion, and not performed by any kind of attraction. 

 Some are of opinion that, as no kind of impulse of the 

 nutritive juices is required in vegetables, but that these are 

 attracted by the parts which require them, and flow in to take 

 the place of what has been lost ; so neither is there any neces- 

 sity for an impulse in animals, the vegetative faculty in both 

 working alike. But there is a difference between plants and 

 animals. In animals, a constant supply of warmth is required 

 to cherish the members, to maintain them in life by the vivi- 

 fying heat, and to restore parts injured from without. It is 

 not merely nutrition that has to be provided for. 



