THE HEART 111 



pulse which it communicates is not synchronous with 

 the apex- beat, but is diastolic in time, and really due 

 to the filling of the chamber and not to its contrac- 

 tion. During systole in such a case the epigastrium 

 recedes. 



Tracings of the apex-beat will be found in any work 

 on physiology, but clinically they are of little interest. 



The Pericardium. 



The pericardium corresponds to the tunica adventitia 

 of the arteries, and is to some extent a protection to the 

 heart. It has been argued that it tends to prevent 

 dilatation of the heart under sudden strain (acting like 

 the outer case of a football or the netting round an 

 indiarubber spray bag), but this can only be true of 

 extreme emergencies.* Certainly a sudden paralytic 

 dilatation of the heart sufficient to cause its arrest does 

 not seem to be prevented by the pericardium. Nor does 

 free movement between the surface of the heart and the 

 inner aspect of the pericardium appear to be essential to 

 the unhampered action of the former, for clinical observa- 

 tion shows that, provided the heart muscle has escaped 

 damage in the process which leads to the pericardial 

 adhesion, little, if any, hypertrophy of the heart ensues. 

 As the space inside the pericardium is strictly limited, 

 it seems not unlikely that great enlargement of one side 

 of the heart must interfere with the action, and especially 

 with the filling, of the other. Thus, for example, the 



* See Theodore Fisher, 'Dilatation of the Heart,' Lancet, 1902, 

 i. 1594. 



