VII 



MECHANICS OF THE HEART 



225 



It follows that the apex of the heart does not approach the base, 

 but on the contrary the base approaches the apex, so that the 

 latter is energetically thrust against the thoracic wall and produces 

 the cardiac beat. It may, however, be objected to this ingenious 

 experiment that the sharp lift produced by the cardiac impulse 

 takes place not during the period of efflux, but in that of 

 tension. 



The same reason invalidates the doctrine of the recoil (recul 

 balastique) supported particularly by Skoda (1842) and Htffelsheim 

 (1854), which in so far as it assumes locomotion of the heart 

 resembles the preceding. It is also contrary to the fact that the 

 cardiac pulse is not confined to the region of the apex in the fifth 

 intercostal space, but (as we have seen) is even more frequently 

 accentuated in the fourth intercostal space. 



FIG. 81. The upper tracing is an artificial cardiogram, obtained from a perfected model. The 

 lower tracing is a cardiogram taken on man. In both tracings the rise O represents the effect 

 of presystole ; the rise V, the effect of systole. (Marey.) 



Still more inadequate is the theory maintained by Senac 

 (1749), Bahr (1862) and others, which derives the cardiac pulse 

 from the downward impulse of the apex in consequence of the 

 distension of the arterial arches (aortic and pulmonary) determined 

 by the pressure produced in these by each wave of blood that 

 surges from the heart. We have seen that the apex is the least 

 mobile point of the heart in the longitudinal direction, because the 

 elongation of the arterial arches almost exactly compensates for 

 the systolic shortening. 



All these mechanical factors intervene as accessory and com- 

 plementary data in the production of the ictus, during the period 

 of systolic evacuation ; but the essential and fundamental cause of 

 the phenomenon is the tension and hardening of the heart during 

 the whole period of systole. The heart is in perpetual contact with 

 the internal wall of the thorax and the external parts of the lungs, 



VOL. I Q 



