108 APPLIED PHYSIOLOGY 



former of these periods that the apex-beat is produced. 

 The greater the resistance offered to the escape of blood 

 from the ventricles, the more prolonged is the com- 

 pression period required, and the longer, therefore, the 

 systole.* Hence the slow systole of aortic stenosis and 

 high arterial pressure. It is now generally believed 

 that the systole never succeeds in expelling the whole of 

 the blood contained in the ventricles ; a fraction is 

 always left behind. If the systole is feeble, this fraction 

 is increased, and may be so great as to retard the whole 

 current of blood through the heart, in consequence of 

 which all the signs of back pressure may result even in 

 the absence of any valvular defect. To this condition 

 the term ' systole catalectic ' is sometimes applied.f 



After their contraction, the walls of the ventricles 

 rebound in diastole. Whether this is due merely to an 

 elastic recoil of the compressed columnse carnese and 

 musculi papillares, or whether there is an ' active ' 

 retraction of the muscle fibres, is disputed ; but, at all 

 events, the force of the recoil is sufficient to produce a 

 degree of negative pressure in the ventricular cavities. 

 It is still denied by some physiologists that this is of 

 sufficient degree to aid in the filling of the heart, but it 

 seems to play a larger part in some conditions of disease. 

 One cannot explain the diastolic murmur met with in 

 some cases of mitral stenosis, for instance, unless on the 



* Even when the aortic pressure is high, the compression time 

 does not seem to be much prolonged so long as the heart muscle is 

 healthy. As Hill points out, this is equivalent to saying that the 

 heart can meet great demands on its powers without any appreciable 

 loss of time (Schafer's ' Physiology,' ii. 20). 



f Graham SteelL 



