112 ABNORMALITIES OF THE HEART-BEAT. 



The cause of the second sound of the heart, according to the gener- 

 ally accepted view, is the abrupt closure of the semilunar valves. It 

 is, therefore, said to be chiefly a valvular sound. It is, however, in part 

 due also to a sudden concussion of the fluid particles in the large arterial 

 vessels. 



Landois has shown from apex-beat curves taken from healthy in- 

 dividuals that the semilunar valves of the aorta and those of the pul- 

 monary artery do not close at the same time. As a rule, however, the 

 difference in time is so slight that the two sets of valves generate only 

 one sound. On the other hand, if, owing to increase of the difference 

 in pressure in the aorta and in the pulmonary artery, this interval be- 

 comes greater, a duplication or splitting of the second sound may become 

 quite perceptible. This may occur in perfectly healthy individuals, 

 especially at the end of inspiration or at the beginning of expiration. 

 It is important to remember, however, that although the second sound 

 corresponds with the closure of the semilunar valves, it appears proved 

 that the closure itself gives rise to no sound ; it is only an instant later, 

 when the tension of the valves becomes greater, that the second sound 

 becomes audible. 



It is generally believed that the points on the chest-wall at which the heart- 

 sounds are heard most distinctly on auscultation correspond to the points in the 

 neighborhood of which they are produced. 



The first valvular sound produced at the right auriculo-ventricular orifice is 

 heard most distinctly at the junction of the fifth rib with the sternum on the 

 right side, and is transmitted from that point somewhat inward and obliquely 

 upward along the sternum (Fig. 34, i). As the left auriculo-ventricular orifice is 

 directed more posteriorly, toward the interior of the thorax, and is covered in 

 front by the arterial orifices, the first mitral valvular sound is heard best at the 

 apex or immediately above it, where a strip of the left auricle is in immediate 

 contact with the chest-wall (1^ I) . As the orifices of the aorta and pulmonary 

 artery are so close together, it is advisable to listen for the aortic second heart- 

 sound in the prolongation of the axis of the aorta, that is, at the right border 

 of the sternum, at the inner extremity of the right costal cartilage (at 2). The 

 pulmonic second heart-sound is heard most distinctly in the second left intercostal 

 space a little to the left and beyond the edge of the sternum (at II). The aortic 

 second sound is clearer, sharper, and shorter, and is heard over a larger area than 

 the pulmonic second sound. 



To determine the intensity of the heart-sounds quantitatively H. Vierordt 

 inserts between the chest-wall and the ear a series of solid rubber plugs, which 

 are poor conductors of sound, placed one upon the other in the form of a column. 



ABNORMALITIES IN THE HEART-BEAT. 



Accentuation of the first sound of the heart in both ventricles indicates a 

 more powerful contraction of the ventricular muscle and a consequent, sudden, and 

 increased tension of the auriculo-ventricular valves. 



Accentuation of the second sound is a sign of increased tension in the interior 

 of the corresponding large vessels. Hence accentuation of the pulmonic second 

 sound, which is such an important diagnostic sign, always indicates hyperemia 

 and excessive tension in the lesser circulation. 



Feeble heart-sounds are caused by sluggish, weakened heart-action or abnormal 

 ischemia; they are observed particularly in cases of morbid degeneration of the 

 heart-muscle. The cause of weakness of individual heart-sounds can be deduced 

 from the foregoing explanation. 



The term embryocardia is used when the two sounds of the heart are exactly 

 alike with respect to strength and the intervals between heart-beats, resembling 

 the ticking of a clock; the phenomenon indicates weakening of the heart-muscle. 



Irregularities in the structure of individual valves may render the heart- 

 sounds impure by causing irregular vibrations. When pathological cavities filled 

 with air are present in the immediate neighborhood of the heart, they may act as 



