266 MANUAL OF PHYSIOLOGY. 



and the ventricles become distended, their flaccid walls appear to 

 be drawn over the liquid mass by the contracting auricles, just as 

 a stocking is drawn over the foot by the hands, and their walls 

 seem to approach towards the base of the heart. The moment 

 the ventricles have received their full charge of blood from the 

 auricles, they contract, becoming shorter by the movement of the 

 base towards the apex, and thicker by the elongated ventricular 

 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 forwards, and 

 the apex also forwards and towards the right. On the ventricular 

 systole ceasing the gradual refilling of the auricles begins ; the 

 ventricles become flaccid and flattened ; the semilunar valves 

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

 steady resilient pressure force it onwards towards 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- 



