THE CIRCULATION OF THE BLOOD AND LYMPH 81 



the ear, and the peculiar booming character of the first sound 

 may be due to the superposition of these various resonance tones 

 upon the muscular note. But, in addition, the vibration of the 

 auriculo-ventricular valves undoubtedly contributes to the pro- 

 duction of the sound, and some observers have been able to 

 distinguish in the first sound the valvular and the muscular 

 elements, the former being higher in pitch than the latter, but 

 a minor third below the second sound. In the excised empty 

 heart the deeper tone of the first sound is alone heard, while 

 the higher note is elicited when in a dead heart the auriculo- 

 ventricular valves are suddenly put under tension (Haycraft). 

 When the mitral valve is prevented from closing by experimental 

 division of the chordae tendineae, or by pathological lesions, the 

 first sound of the heart is altered or replaced by a ' murmur.' 

 This evidence is not only important as regards the physiological 

 question, but of great practical interest from its bearing on the 

 diagnosis of cardiac disease. It may be added that the point 

 of the chest -wall at which the first sound is most easily recog- 

 nised is also the point at which a changed sound or murmur 

 connected with disease of the mitral valve is most distinctly 

 heard. The sound is, therefore, best conducted from the mitral 

 valve along the heart to the point at which it comes in contact 

 with the wall of the chest. Changes in the first sound con- 

 nected with disease of the tricuspid valve are heard best, in 

 the comparatively rare cases where they can be distinctly 

 recognised, in the third to the fifth interspace, a little to the 

 right of the sternum. 



The second sound is caused by the vibrations of the semi- 

 lunar valves when suddenly closed, ' the recoiling blood forcing 

 them back, as one unfurls an umbrella, and with an audible 

 check as they tighten ' (Watson). The sharpness of its note is 

 lost, and nothing but a rushing noise or bruit can be heard, when 

 the valves are hooked back and prevented from closing. It 

 is altered, or replaced by a murmur when the valves are diseased. 

 As there is a mitral and a tricuspid factor in the first sound, so 

 there is an aortic and a pulmonary factor in the second. The 

 place where the second sound is best heard (over the junction 

 of the second right costal cartilage and sternum) is that at which 

 any change produced by disease of the aortic valves is most 

 easily recognised. The sound is conducted up from the valves 

 along the aorta, which comes nearest to the surface at this 

 point. Changes connected with disease of the pulmonary 

 valves are most readily detected over the second left intercostal 

 space near the edge of the sternum, for here the pulmonary artery 

 most nearly approaches the chest-wall. The first sound is 

 ' systolic ' that is, it occurs during the ventricular systole ; the 



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