CAUSE OF THE SOUNDS OF THE HEART. 207 



semilunar valves at the orifices of the aorta and pulmonary 

 artery. We remark, however, that the sound is heard with 

 its maximum of intensity over the site of these valves, and is 

 propagated along the great vessels, to which they are attach- 

 ed. It also occurs precisely at the time of their closure ; i. <?., 

 immediately following the ventricular systole. 



The cause of the first sound of the heart has not, until 

 within a few years, been as well understood. It was maintain- 

 ed by Rouanet, that this sound was produced by the sudden 

 closure of the auriculo- ventricular valves ; but the situation 

 of these valves rendered 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. Con- 

 clusive observations on this point were made a few years ago 

 by Dr. Flint, constituting part of an essay which received 

 the prize of the American Medical Association in 1858. 1 



The following facts were developed in this essay : 



1. If a folded handkerchief be placed between the stetho- 

 scope and integument, the first sound is divested of some of 

 its most distinctive features. It loses the quality of impul- 

 sion, and presents a well-marked valvular quality. 



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

 the prsecordia, while the subject is in a recumbent posture, and 

 the heart by force of gravity is removed 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 will present only its valvular 

 element. 



1 AUSTIN FLINT, Prize Essay on the Heart-Sounds in Health and Disease. 

 Transactions of the American Medical Association, 1858. 



