SOUNDS OF THE HEAET. 45 



which produces the impulse against the walls of the thorax, and as will be 

 seen farther on, the dilatation of the arterial system, indicated by the pulse. 

 It is natural, therefore, in studying these phenomena, to take the systole as a 

 point of departure, instead of the action of the auricles ; and the sounds, 

 which are two in number, have been called first and second, with reference to 

 the ventricular systole. 



The first sound is absolutely synchronous with the apex-beat. The second 

 sound follows the first with scarcely an appreciable interval. Between the 

 second and the first sound, there is an interval of silence. 



Some writers have attempted to represent the sounds of the heart and 

 their relations to each other, by certain syllables, as " lubb-dup or lubb-tub " ; 

 but it seems unnecessary to attempt to make such a comparison, which can 

 only be appreciated by one who is practically acquainted with the heart- 

 sounds, when the sounds themselves can be so easily studied. 



Both sounds are generally heard with distinctness over the entire prsecor- 

 dial region. The first sound is heard with its maximum of intensity over 

 the body of the heart, a little below and within the nipple, between the 

 fourth and fifth ribs, and is propagated with greatest intensity downward, 

 toward the apex. The second sound is heard with its maximum of intensity 

 at the base of the heart, between the nipple and the sternum, at about the 

 third rib, and is propagated upward, along the course of the great vessels. If 

 the stethoscope be placed between the point of the apex-beat and the left 

 nipple, the first sound will be heard strongly accentuated, and presenting a 

 certain quality in its valvular element, due to the closure of the mitral valve. 

 If the stethoscope be then removed to a point a little to the left of the ensi- 

 form cartilage, the element due to the closure of the tricuspid valve will 

 predominate, and a slight but distinct difference in quality may frequently 

 be noted. An analogous difference in the valvular elements of the second 

 sound may also be observed. When the stethoscope is placed at the base of 

 the heart, just to the right of the sternum and over the aortic valves, the 

 character of "the second sound is often notably different from the character of 

 the sound heard with the stethoscope placed just to the left of the sternum, 

 over the pulmonic valves. In this way the valvular elements of the two 

 sounds of the heart may be separated, each one into two, one produced by 

 closure of the valves on the left side, and one by closure of the valves of the 

 right side. A recognition of these nice distinctions is useful in physical 

 examinations of the heart in disease. 



The rhythm of the sounds bears a definite relation to the rhythm of the 

 heart's action. Laennec was the first to direct special attention to the rhythm 

 of the heart-sounds, although the sounds themselves were recognized by Har- 

 vey, who compared them to the sounds made by the passage of fluids along 

 the oesophagus of a horse when drinking. Laennec divided a single revolution 

 of the heart into four equal parts : the first two parts, occupied by the first 

 sound ; the third part, by the second sound ; and the fourth part, with no 

 sound. He regarded the second sound as following immediately after the 

 first. Some authors have described a " short silence " as occurring after the 

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