(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 expelled;
(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 into them, being filled like sacs or bladders, and not expanding like bellows. These conclusions are confirmed by the jerking way in which blood flows from a cut artery.