THE HEART 135 



Of alterations in rate due to augmentor impulses we 

 know nothing, but it seems not unreasonable to suppose 

 that the rapid and forcible beat of excitement may be 

 induced in that way.* Experiment, however, has shown 

 that stimulation of the accelerator does not raise the 

 heart rate above 120 per minute. 



2. In health, no matter how fast or how slowly the 

 heart may be beating, the relative duration of systole 

 and diastole remains unaltered. If the cardiac muscle 

 is diseased, however, or if nervous influences are at work, 

 the normal relative duration of the different phases of 

 the cardiac cycle is often disturbed. Such disturbance 

 can be recognized at the bedside by changes in the 

 spacing of the heart sounds. In early life irregularity of 

 rhythm is chiefly due to occasional prolongation of the 

 diastole. In later life the occurrence of premature 

 systoles is a more potent source of varying rhythm. 



The following alterations may occur : 



2 Normal. 



-2 Prolongation of systole (pen- 

 dulum rhythm). 

 Shortening of systole. 



Prolongation of diastole (brady- 

 cardia). 



1212121212 Shortening of systole and dia- 

 stole (tic-tac rhythm). 



1 2 1 2 1 2 1 Shortening of diastole (tachy- 

 cardia). 



(a) The systole may be unduly prolonged from in- 



* Determann, 'Ueber Herz-und Gefassneurosen,' Volkmanris 

 Samml. Klin. Vort., 1894, Inn. Med., Nr. 30, p. 1. 



