THE MECHANISM OF THE HEART PUMP 1021 



systole. The same disappearance of the normal second sound is 

 observed in cases where the valves are prevented from closing by 

 diseased conditions. 



The pulmonary and aortic valves generally close simultaneously. 

 In some cases, however, the aortic may close slightly before the 

 pulmonary, giving rise to a ' reduplicated second sound.' The 

 pulmonary element of this sound is best heard over the second left 

 cartilage, or in the second left intercostal space. 



The first sound has probably a twofold origin, viz. from the sudden 

 closure of the auriculo-ventricular valves and from the contraction of 

 the thick muscular wall of the ventricle. 



If the veins going to the heart be clamped so that the heart can 

 no longer be distended with blood nor the valves put on the stretch, 

 the second sound is altered in character, but not abolished. The first 

 sound may indeed be heard on listening with a stethoscope to the beat 

 of an excised heart. It is said that two notes may be detected in the 

 first sound a high note of short duration due to closure of the valves, 

 and a low-pitched note due to the muscular contraction. The muscular 

 element of the first sound has the same pitch as the sound produced 

 by contracting voluntary muscle, and therefore as the resonance-tone 

 of the ear. This consideration prevents our arguing from the tone that 

 a cardiac contraction is a tetanus. As we shall show later on, each 

 ventricular contraction is analogous to a simple muscle-twitch and not 

 to a tetanus. 



THE THIRD HEART SOUND. A number of observers have described a third 

 heart sound as occurring in certain individuals during the diastole, a short time 

 after the second sound. It is softer and of a lower pitch than the second sound, 

 and is heard most distinctly over the apex beat. It is probably due to the vibra- 

 tions set up in the fluid itself or in the auriculo-ventricular valves by the sudden 

 inrush of blood from auricles to ventricles at the beginning of diastole. The sound 

 is shown objectively by the vibrations on the endocardiac pressure curve given 

 in Fig. 399 (Straub). It has also been registered electrically by Einthoven. 



CARDIAC MURMURS 



When a fluid escapes through a narrow orifice into a wider space 

 vibrations are set up in the fluid and may be transmitted by any 

 elastic medium to the ear, giving rise to the sensation of sound. Such 

 a sound is produced when water is allowed to run from a tap into a 

 vessel of water, or when air is blown out between the partially closed 

 lips. The formation of such vibrations forms, indeed, the basis for the 

 construction of many musical instruments. The same sort of vibration 

 may be set up in the large vessels or in the heart, whenever the blood 

 passes rapidly through a narrow orifice into a wider space. 



In the normal individual sounds produced in this way are so slight 

 that they may be neglected ; under abnormal conditions, as after 



