DILATATION OF THE HEART. 



331 



ment as it should be when that movement is complete. Blood 

 continues to enter as long as the pressure of the afferent vessels upon 

 their contents exceeds the power of resistance of the walls of the 

 cardiac cavity. Let us, for instance, suppose an obstacle to exist at the 

 root of the pulmonary artery, or, what is more likely, an obstruction in 

 the current of the capillary system of the lungs. Such obstacle can- 

 not prevent a systolic contraction of the right ventricle^ although no 

 doubt it may have the effect of preventing the ventricle from expel- 

 ling the whole of its contents. Now, as long as the pressure upon the 

 blood within the vena cava is greater than the resisting power of the 

 thin walls of the right ventricle, the ventricle will be distended by 

 an abnormal influx of blood. Moreover the diastolic relaxation is ter- 

 minated by a contraction of the right auricle, whose contents are forci- 

 bly propelled into the right ventricle. As the blood enters the heart 

 by the veins, and enters it under quite a moderate pressure, it is mani- 

 fest that the right auricle and ventricle, the thickness of whose walls 

 is only one and two lines, respectively, should be much more liable 

 to dilatation than the left ventricle, whose ventricular wall has a thick- 

 ness of five lines ; and, in fact, we find that the auricles are the most 

 frequent seat of dilatation ; next to these, the right ventricle, while di- 

 latation of the left ventricle is the rarest of all. 



A considerable degree of dilatation of the left ventricle arises in 

 cases of deficience of the aortic valves, and a smaller degree in de- 

 ficience of the mitral ; and this circumstance, which is taught in every 

 text-book on pathological anatomy, also argues in favor of the correct- 

 ness of the above deductions. Let us suppose that the aortic valves are 

 insufficient, and that blood regurgitates from the aorta into the left ven- 

 tricle during its period of diastole, the pressure which the blood exerts 

 upon the relaxed cardiac wall is then a very considerable one, and 

 capable of overcoming the resisting power of the latter. Barriberger 

 has made a careful examination of fifty hearts with valvular disease ol 

 the aorta, with regard to the coexistence of dilatation and hypertrophy 

 of the left ventricle, and has arrived at the following conclusions, 

 which fully agree with our views as to the pathogeny of dilatation of 

 the heart. He found that, in simple contraction at the root of the 

 aorta, there is no dilatation, or else only a very slight dilatation of the 

 left ventricle. Although the obstacle to the circulation is very great in 

 these cases, there is no increase of that internal pressure, during dias- 

 tole, by which alone the dilatation of the ventricle is caused. On the 

 other hand, in insufficience of the aortic valves, there is always a con- 

 siderable dilatation of the left ventricle, which predominates over the 

 coexisting hypertrophy. There is often room enough in the dilated 

 ventricle to contain a full-sized fist. In such cases, as we have 



