272 MANUAL OF PHYSIOLOGY. 



cone becoming rounder. The great arteries are at the same time 

 distended with blood and elongated, their elastic walls being 

 drawn down over the liquid wedge on its exit from the ventricle. 

 The soft, elastic tissues are thus in turn made to slide, as it were, 

 over the incompressible fluid blood that forms the fulcrum, which 

 the power of the muscular walls uses as a firm purchase. During 

 the systole, when the thorax is open, the ventricles rotate slightly 

 on their long axis, so that the left comes a little forward, and 

 the apex also forward and toward the right. On the ventricular 

 systole ceasing the ventricles become flaccid and flattened, and 

 the gradual refilling of the cavities begins; the semiluuar valves 

 being closed, the large arteries grasp firmly the blood, and by their 

 steady resilient pressure force it onward toward the distal ves- 

 sels. During this pause the arteries seem to become shorter, 

 drawing the base of the heart up again and lengthening the flac- 

 cid ventricles. 



The part of the heart which changes its position most is the 

 line between the auricles and ventricles, while the apex remains 

 fixed in the one position, only making a very slight lateral and 

 forward motion, which probably does not take place during life. 

 If a needle with a light lever attached be made to enter the apex 

 through the wall of the chest, the lever does not move in any 

 definite direction during the systole, but simply shakes. If, on 

 the other hand, the needle be placed in the base of the ventricles, 

 the lever moves up and down with each systole and diastole. 



HEART'S IMPULSE. 



If the ventricles be gently held between the fingers during their 

 systole, a most striking sensation is given by the sudden harden- 

 ing of the muscle. The mass of the ventricles, from being quite 

 soft and compressible during diastole, suddenly acquires a wooden 

 hardness, owing to the tightness with which the muscle grasps the 

 fluid, and the greater firmness of the contracting tissue. 



This hardening gives the sensation of a sudden enlargement in 

 all directions. No matter on what surface the finger be placed, 

 the heart seems to move in that direction, so as to give a slight 

 knock or impulse. Thus, when grasped between the forefinger 



