80 III I] APEX-BEAT. 



(2.) Hypertrophy of the Ivft auricle occurs in stenosis of the left auriculo-ven- 

 tricular orifice, or iu insufficiency of the mitral valve, and it occurs also as a result 

 of aortic insufficiency, because the auricle has to overcome the continual aortic 

 pressure within the ventricle. 



(3.) Hypertrophy of the riyht ventricle, occurs (a. ) when there is resistance to 

 the blood-stream through the pulmonary circuit. The resistance may be due to 

 (.) obliteration of large vascular areas in consequence of destruction, shrinking or 

 compression of the lungs, and the disappearance of numerous capillaries in emphy- 

 sematous lungs. (jS.) Overfilling of the pulmonary circuit with blood in conse- 

 quence of stenosis of the left auriculo-ventricular orifice or mitral insufficiency 

 consequent upon hypertrophy of the left auricle resulting from aortic insufficiency. 

 (b. ) Hypertrophy of the right ventricle will also occur when the valves of the 

 pulmonary artery are insufficient, thus permitting the blood to flow back into the 

 ventricle, so that the pressure within the pulmonary artery prevails within the 

 right ventricle (very rare). 



(4.) Hypertrophy of the rirjlit auricle occurs in consequence of the last-named 

 condition, and also from stenosis of the tricuspid orifice, or insufficiency of the 

 tricuspid valve (rare). If several lesions occur simultaneously, the result is 

 complex. 



Artificial Injury to the Valves. 0. Rosenbach has made experiments on 

 the action of the heart when its valves are injured artificially. If the aortic valves 

 are perforated, with or without simultaneous injury to the mitral or tricuspid 

 valves, the heart does more work ; thus the physical defect is overcome for a time, 

 so that the blood-pressure does not fall. The heart seems to have a store of 

 reserve energy, which is called into play. Soon, however, dilatation takes place, 

 on account of the regurgitatiou of the blood into the heart. Hypertrophy then 

 occurs, but the compensation meanwhile must be obtained through the reserve 

 energy of the heart. 



Impeded Diastole. Among causes which hinder the diastole of the heart are 

 copious effusions into the pericardium, or pressure of tumours upon the heart. The 

 systole is greatly interfered with when the heart is united to the pericardium and 

 to the connective tissue in the mediastinum. As a consequence the connective 

 tissue, and even the thoracic wall, are drawn in during contraction of the heart, 

 so that there is a retraction of the region of the apex-beat during systole, and a 

 protrusion of this part during the diastole. 



50. The Apex-Beat The Cardiogram. 



Cardiac Impulse. By the term " apex-beat" or cardiac impulse, is 

 understood under normal circumstances an elevation (perceptible to 

 touch and sight) in a circumscribed area of the fifth left intercostal 

 space, caused by the movement of the heart. [The apex-beat is felt in 

 the fifth left intercostal space, two inches below the nipple, and one 

 inch to its sternal side.] The impulse is more rarely felt in the fourth 

 intercostal space, and it is much less distinct when the heart beats 

 against the fifth rib itself. The position and force of the cardiac 

 impulse vary with changes in the position of the body. 



[Methods. To obtain a curve of the apex-beat or a cardiogram, we may 

 use one or other of the following cardiographs (Fig. 25). Fig. 25, A, is the 

 first form used by Marey, and it consists of an oval wooden capsule applied in an 



