332 DISEASES OF THE HEART. 



shown, the wall of the ventricle is subjected to an extreme pres- 

 sure. Bamberger found that the greatest degree of dilatation of the 

 left ventricle arose when the aortic valves were the seat of simultane- 

 ous contraction and insufficience, as then such a condition would natu 

 rally be the most favorable one for the occurrence of dilatation ; since 

 the stenosis prevents a complete emptying of the ventricle during 

 systole, while, owing to the insufficience, the blood regurgitates into the 

 ventricle during the diastole, with all the force which the pressure of 

 the aorta can impart. 



The occurrence of a slighter degree of dilatation in insufficience of 

 the mitral is likewise easy to account for. When the mitral valve is 

 not effectually closed, a considerable amount of blood regurgitates 

 from the ventricle during the systolic movement, so that the auricle and 

 pulmonary veins become overloaded and their walls tightly stretched. 

 Blood consequently pours into the left ventricle with unnatural 

 force during diastole. Perhaps the hypertrophy of the left auricle 

 and the increased energy of its contractile power also aid in causing 

 the left ventricle to yield to the abnormal pressure, when the mitral 

 valve is insufficient. 



In stricture of the left auriculo-ventricular orifice also, there is a con- 

 siderable degree of engorgement of the left auricle, and pulmonary 

 vein, and the auricle itself becomes hypertrophied, but the augmenta- 

 tion of propulsive power is neutralized by the obstacle to the 

 entrance of the blood. This i's plainly the reason why the left ventricle 

 is dilated when the mitral valve is insufficient, but does not dilate 

 where the valve is only contracted. 



Dilatation of the heart, when arising solely from an increase of the 

 pressure of the blood within the cardiac cavities, as a rule, is soon fol- 

 lowed by excentric hypertrophy, the continuous and abnormally active 

 contractions of the organ giving rise to a multiplication of its muscu- 

 lar fibres. When we come to treat of valvular disease, we shall ex- 

 plain more in detail that it is by this transition from dilatation into 

 excentric hypertrophy that the effect of obstruction to the circulation, 

 arising from derangement of the valves, is counteracted. 



2. Dilatation of the heart may arise from the loss of tone of tho 

 cardiac wall, owing to disease of its substance, in consequence of which 

 the wall gives way even before the normal internal pressure exerted 

 upon it during diastole. Even the simple serous infiltration to which 

 the heart is subject in the various forms of inflammation which affect 

 it, especially in pericarditis, diminishes the resisting power of the or- 

 gan and causes it to dilate. Sometimes its muscles seem to undergo 

 an atrophy, like that suffered by the muscles of the rest of the body 

 after severe and protracted illness, and in consequence of which the 



