950 PHYSIOLOGY 



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 first 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. .4s 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 vibrations 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 the diastole. The sound is shown objectively 

 by the vibrations on the endocardiac pressure curve given in Fig. 410 (Straub). It li.i^ 

 also been registered electrically by Einthoven. 



CARDIAC MURMURS 



When a fluid escapes through a narrow orifice into a wider space, vibra- 

 tions 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 

 inst ruments. 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 thoy may be neglected; under abnormal conditions, as after diso;i 

 anVotini; tho, valvular orifices of the heart, this vibration may occur during 

 every heart cycle and be heard with ease on applying tho oar to the chost . 

 Those inimimrs, <>r hruilx as tlioy aro oallod. aro of paramount importance 

 in enabling tho modiral man to form a judgment as to the condition of the 



