88 FATHERS OF BIOLOGY. 



(4) That the pulse is not produced by the arteries 



enlarging and so filling, but by the arteries 



being filled with blood and so enlarging. 



We can now consider the method by which Harvey 



arrived at these results. The work, " De Motu Cordis 



et Sanguinis," after giving an account of the views of 



preceding physiologists, ancient and modern, commences 



with a description of the heart as seen in a living animal 



when the chest has been laid open and the pericardium 



removed. Three circumstances are noted 



(a) The heart becomes erect, strikes the chest, and 



gives a beat ; 



(b) It is constricted in every direction ; 



(c) Grasped by the hand, it is felt to become harder 



during the contraction. 

 From these circumstances it is inferred 



(1) That the action of the heart is essentially of the 



same nature as that of voluntary muscles, which 

 become hard and condensed when they act ; 



(2) That, as the effect of this, the capacity of the 



cavities is diminished, and the blood is ex- 

 pelled ; 



(3) That the intrinsic motion of the heart is the systole, 



and not the diastole, as previously imagined. 

 The motions of the arteries are next shown to be 

 dependent upon the action of the heart, because the 

 arteries are distended by the wave of blood that is thrown 



