CAUSE OF THE CARDIAC IMPULSE. 



63 



ab. Thus, the long diameter of the ellipse (FG) is diminished, the small diameter 

 dc is increased, while the base is brought nearer to the chest-wall e. This alone 



Curves from the apex-beat. A, normal curve (man) ; B, from a dog ; C, very rapid curve 

 (dog) ; D and E, normal curves (man) registered on a vibrating glass plate where each 

 indentation = "01613 sec. In all the curves ab means contraction of the auricles, and 

 be of the ventricles ; d, closure of the aortic, and e, of the pulmonary valves ; ef, diastole 

 of the ventricle. 



does not cause the impulse, but the basis of the heart, being hardened during the 

 systole and brought nearer to the chest-wall, allows the apex to execute the move- 

 ment which causes the impulse (p. 61). 



(2) During relaxation, the ventricle lies with its apex (fig. 40, II., i) obliquely 

 downwards, and with its long axis in an oblique direction so that the angles (bci, 

 uci) formed by the axis of the ventricles with the diameter of the base are unequal 

 during systole it represents a regular cone, with its axis at right angles to its 

 base. Hence, the apex (i) must be erected from below and behind (/>), forwards 

 and upwards (Harvey " cor sese erigere "), and when hardened during systole 

 presses itself into the intercostal space (fig. 40, II.). 



(3) The ventricles undergo during systole a slight spiral twisting on their long 

 axis (" lateralem inclinationem " Harvey), so that the apex is brought from 

 behind more forward, and thus a greater portion of the left ventricle is turned to 

 the front. This rotation is caused by the muscular fibres of the ventricles, which 

 proceed from that part of the fibrous rings between the auricles and ventricles 

 which lies next the anterior thoracic wall. The fibres pass from above obliquely 

 downwards, and to the left, and also run in part upon the posterior surface of the 

 ventricles. When they contract in the axis of their direction, they tend to raise 

 the apex, and also to bring more of the posterior surface of the heart in relation 

 with the anterior thoracic wall. It is favoured by the slightly spiral arrangement 

 of the aorta and pulmonary artery. 



These are the most important causes, but the minor causes are, 



(4) The " reaction impulse " or " recoil" or that movement which the ventricles 

 are said to undergo, (like an exploded gun or rocket), at the moment when the 



