DISEAS'^S OF THE IIRART. — VALVULAR DEFECTS. 289 



a mere slit, the mitral valve forming a rigid diaphragm between 

 the auricle and ventricle. The fusion of the chorda3 tendlnea^ 

 (fig. 90) starts from their points of bifurcation and their oblique 

 insertion into the under surface of the valve. Tliis contributes 

 not a little to the rigidity and immobility of the valve. 



Clinical Applicatioxs of the above State:n[ents. 



It is obvious that the existence of valvular defects must cause pro- 

 found disturbances, first in the movement of the blood, and secondly in 

 the functions of the various organs. Valvular lesions, whether due to 

 chronic changes or to acute endocarditis, may, from this point of view, 

 be grouped under two heads : 



1. Thickening, rigidity, calcification and coalescence of the valves 

 prevent their being accurately applied at the right moment to the wall of 

 the vessel or the ventricle (sc. in the case of the aortic valves, during the 

 systole, in that of the mitral, during the diastole), so that the valve con- 

 tinues to project into the corresponding orifice, narrowing its lumen 

 {stenosis). The blood-current impinges upon this obstacle and so causes 

 a murmur which is best heard at that point of the thoracic wall, to which 

 it is most directly conducted. 



2. Retraction, perforation and partial detachment of valves, and 

 rupture of chorda? tendinea), prevent the valves from completely closing 

 their respective orifices, at the moment when their tension ought to bo 

 opposed to the regurgitant current of the blood ; an opening is con- 

 sequently left, through which the blood returns into the cavity from 

 which it has just been driven {Insujjlciency). The closure of the valves 

 is normally accompanied by two audible sounds ; the first, systolic in 

 rhythm, is due to the tension of the mitral valve ; the second, diastolic 

 only, to that of the semilunar valves. Now if this sudden tension does 

 not occur, the corresponding sound must also be wanting. In its place 

 we may have a murmur caused by the regurgitation of the blood through 

 the abnormal orifice ; a murmur which may indeed be intense, but must 

 always be of short duration. Stenosis and insufficiency always occur 

 together aa a result of chronic endocarditis ; acute endocarditis, how- 

 ever, by cansing perforation and detachment, may be followed by in- 

 sufficiency without stenosis. 



a. Stemsls and Insufidency of tho Aortic Valves (figs. 89 and 92). 



The left ventricle of an adult pumps about three ounces of blood (d; 

 wineglassful) into the aortic system at each systole. The increased resist- 

 ance offered by the contracted aortic orifice is transferred as an increase of" 

 systolic pressure to the internal surface of the left ventricle, and, accord- 

 ing to the law laid down in § 235, must lead to its hypertrophy. At the 

 same time the stenosis will cause a systolic murmur which will be most 



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