SOUNDS OF THE HEAET. 47 



point where the first sound is heard with its maximum of intensity, it pre- 

 sents only its valvular element. 



These observations, taken in connection with the fact that the first sound 

 occurs when the ventricles contract and necessarily accompanies the closure 

 of the auriculo-ventricular valves, show that these valves produce at least one 

 element of the sound. In farther support of this opinion, is the fact that the 

 first sound is heard with its maximum of intensity over the site of the valves 

 and is propagated downward along the ventricles, to which the valves are 

 attached. Actual experiments are not wanting to confirm this view. Chauveau 

 and Faivre succeeded in abolishing the first sound by the introduction of 

 a wire ring into the auriculo-ventricular orifice through a little opening in 

 the auricle, so as to prevent the closure of the valves. When this is done, 

 the first sound is lost ; but on taking it out of the opening, the sound returns. 

 These observers also abolished the first sound by introducing a small curved 

 tenotomy-knife through the auriculo-ventricular orifice and dividing the 

 chordae tendineae. In this experiment a loud rushing murmur took the place 

 of the sound. These observations and experiments seem to settle the fact 

 that the closure of the auriculo-ventricular valves produces one element of 

 the first sound. 



The other elements which enter into the composition of the first sound 

 are not so prominent as the one just mentioned, although they serve to give 

 it its prolonged and "booming" character. These elements are a sound 

 like that produced by any large muscle during its contraction, called by some 

 the muscular murmur, and the sound produced by the impulse of the heart 

 against the walls of the chest. 



There can be no doubt that the muscular murmur is one of the elements 

 of the first sound ; and it is this which gives to the sound its prolonged char- 

 acter when the stethoscope is applied over the body of the organ, as the sound 

 produced in muscles continues during the whole period of their contraction. 

 Admitting this to be an element of the first sound, its duration must neces- 

 sarily coincide with that of the ventricular systole. 



The impulse of the heart against the walls of the thorax also has a share 

 in the production of the first sound. This is demonstrated by noting the 

 difference in the sound when the subject is lying upon the back, and when 

 he is upright, by interposing any soft substance between the stethoscope and 

 the chest, or by auscultating the heart after the sternum has been removed. 

 Under these conditions, the first sound loses its booming character, retaining, 

 however, the muscular element when the instrument is applied to the exposed 

 organ. 



The observations showing the valvular character of one of the elements 

 of the first sound have been so definite and positive in their results that one 

 can hardly regard them as entirely controverted by the recent experiments 

 (1885) of Yeo and Barrett, upon the hearts, cut from the body, of cats and 

 dogs, which show, it is claimed, that " a definite and characteristic tone sim- 

 ilar in quality to the first sound is produced by the heart-muscle under cir- 

 cumstances that render it impossible for any tension of the valves to contrib- 



