DISEASE OF THE MITRAL VALVE. 367 



nypcrtrophied and dilated, it is generally small, and its walls are 

 thinner, rather than thicker. We have already accounted for this cir- 

 cumstance. In spite of the violent pressure under which the blood is 

 thrown into the ventricle, its walls encounter a moderate pressure 

 only from within, as the increased propulsive power is neutralized by 

 the greater resistance met with in the contracted ostium. 



SYMPTOMS AND COURSE. The effect of mitral disease upon the 

 circulation must, in the main, be the same as that which we have de- 

 scribed as occurring in uncompensated aortic valvular disorder. 



If, in case of insufficience, a part only of the blood enter the aorta 

 upon systole, the rest regurgitating into the auricle ; or, in a case of 

 constriction, if too little of it flow into the ventricle, upon diastole, it 

 is clear that in either case the amount of blood propelled must be 

 smaller than normal, and its flow must be retarded. In like manner 

 the arteries of the aortic circuit contain too little blood, and contract 

 by virtue of their elasticity, while the blood by which they should be 

 tilled is overloading the pulmonary system. If the latter be incapable 

 of accommodating all the blood, engorgement of the venous system of 

 the aorta must follow. We have seen that hypertrophy of the left 

 ventricle neutralizes all these circulatory derangements in disease of 

 the aorta. A greater portion of them, but not all, may also be reme- 

 died for a time in mitral disease, by hypertrophy of the right ventricle. 



The dilated and hypertrophied right heart propels so large a mass 

 of blood, and propels it with so much power into the vessels of the 

 pulmonary circuit, that the blood in the pulmonary veins is subjected 

 to heavy pressure. In consequence of this, to say nothing of the 

 action of the auricle, the blood pours with such force and rapidity into 

 the left ventricle as to completely neutralize the effect of the constric- 

 tion of the valve. In spite of the constriction, the ventricle receives 

 blood enough ; the aortic contents are not lessened, nor is the circula- 

 tion retarded. In the same way, the fulness and tension of the pul- 

 monary vein prevent any considerable regurgitation into the ventricle, 

 notwithstanding the insufficience of the valve ; indeed, as we have seen, 

 the left ventricle is usually both hypertrophied and dilated, so that, in 

 spite of the regurgitation of a considerable amount of blood, it still re- 

 mains capable of filling the aorta. Retardation of the circulation, with 

 engorgement of the venous system, and a corresponding emptiness of 

 the arteries, is thus averted by a compensating hypertrophy of the 

 right ventricle ; but there is one anomaly, which, in aortic disease, is 

 corrected by hypertrophy of the left ventricle, but which hypertrophy 

 of the right ventricle is unable to obviate when the mitral is diseased. 

 This affection is overcharge of the vessels of the pulmonary circuit. 



Clinical experience entirely corroborates this physiological, or 



