50 CIRCULATION OF THE BLOOD. 



The cause of the first sound of the heart has not, until within a few years, been so 

 well understood. It was maintained by Rouanet that this sound was produced by the 

 sudden closure of the auriculo-ventricular valves; but the situation of these valves ren- 

 dered it difficult to .demonstrate this by actual experiment. We have already seen, that, 

 while the second sound is purely valvular in its character, the first sound is composed of 

 a certain number of different elements ; but auscultatory experiments have been made by 

 which all but the valvular element are eliminated and the character of the first sound 

 made to resemble that of the second. Conclusive observations on this point were made 

 a few years ago by Dr. Austin Flint, constituting part of an essay which received the 

 prize of the American Medical Association in 1858. In this essay, the following points 

 were established : 



1. If a folded handkerchief be placed between the stethoscope and integument, the 

 first sound is divested of some of its most distinctive features. It loses the quality of im- 

 pulsion and presents a well-marked valvular quality. 



2. In many instances, when the stethoscope is applied to the proacordia while the 

 subject is in a recumbent posture and the heart is removed by force of gravity from the 

 anterior wall of the thorax, the first sound becomes purely valvular in character and as 

 short as the second. 



3. When the stethoscope is applied to the chest a little distance from the point where 

 the first sound is heard with its maximum of intensity, it presents only its valvular ele- 

 ment. 



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 pretty conclusively that these valves produce at least one element of the 

 sound. In farther support of this opinion, we have 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 want- 

 ing to confirm this view. Chauveau and Faivre have 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 settle beyond question the fact that the closure of the auriculo-ven- 

 tricular 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 we have just considered, although they serve to give it its pro- 

 longed and u 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 but that the muscular murmur is one of the elements of the 

 first sound ; and it is this which gives its prolonged character 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, 

 we can understand how its duration must necessarily coincide with that of the ventricular 

 systole. We can appreciate, also, how all but the valvular element is eliminated when 

 the stethoscope is moved from the body of the heart, the muscular sound not being prop- 

 agated as completely as the sound made by the closure of the valves. 



The impulse of the heart against the walls of the thorax also contributes to produce 

 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 sub- 

 stance between the stethoscope and the chest, or by auscultating the heart after the 



