CIRCULATION. THE HEART. 139 



made use indifferently of the words " right" or " left heart," 

 "aorta" or "pulmonary artery," because all that is said of 

 the right heart applies equally to the left, and there are no 

 more valves in the pulmonary veins than in the vena cava. 



The phenomena which we have examined in the two hearts 

 are manifested outwardly by particular sounds (first and 

 second sound of the heart) and by the impulse or shock of 

 the heart / there are one impulse and two sounds to every 

 cardiac revolution. 



The impulse of the heart (or shock) consists in a tremor 

 which we feel against the walls of the thorax : by placing 

 the hand upon the sixth rib, to the right of the nipple, we 

 feel that the heart seems, as it were, thrown at each contrac- 

 tion against the side, like a hammer upon an anvil. But 

 there is really no blow, in the proper sense of the word, 

 because the point of the heart always touches the wall of 

 the thorax, and there is never any separation between them. 

 Indeed, such a separation is inconceivable, there being noth- 

 ing to fill the void which it would occasion, nothing to inter- 

 pose between the heart and the thorax, not even the lung, 

 for there are, in general, four pulsations of the heart to one 

 expansion of the lung. There is thus, at each apparent 

 shock, only a more decided contact between the heart and 

 the corresponding part of the chest wall. Many theories 

 have been adduced to explain this phenomenon, the most 

 generally received of which is that of Hiffelsheim, theory of 

 recoil (du choc en retour). The shock, received by the heart 

 at the instant that the contents of the ventricle are expelled, 

 is compared to the recoil of a gun when it is fired. But this 

 shock is felt on whatever side the heart is touched, even at 

 its lowest part through the diaphragm ; this simple experi- 

 ment refutes the theory of recoil, as not being always appli- 

 cable ; and also overthrows that which is founded on the 

 straightening of the arch of the aorta, under the influence 

 of the flow of blood, the more so because this shock to the 

 heart takes place even in animals which have no arch to the 

 aorta. 



The movement of the heart may be best described by re- 

 membering the changes in form and consistency which the 

 ventricle undergoes at the moment when the systole takes 

 place : it passes from a state of relaxation into one of con- 

 traction, and presses strongly upon its contents in such a 

 manner as to force them into the arterial tree, which already 

 contains blood under tolerably strong tension. Even if the 



