HEART SOUNDS. 269 



HEART SOUNDS. 



The heart's action is accompanied by two distinct sounds, which 

 can be heard by bringing the ear into firm direct contact with 

 the precordial region, or indirectly by the use of the stethoscope, 

 an instrument of which there are many varieties to suit the taste 

 of clinical observers.* 



One sound follows the other quickly, and then comes a short 

 pause; consequently, they are spoken of as the^rs^ and second 

 sounds. 



The first sound occurs at the same time as the ventricular sys- 

 tole. It is a low, soft, prolonged tone, and is most distinctly heard 

 over the fifth intercostal space. 



The second sound is produced when the two sets of semilunar 

 valves are closed, that is, at the moment when the blood ceases 

 to escape from the ventricles. It is a sharp, short sound, and is 

 best heard at the second costal cartilage on the right side. 



The cause of the first sound is as yet involved in doubt. Pos- 

 sibly there are several factors in its production. The principal 

 events occurring at this time may be enumerated thus : 



1. The heart's impulse. 



2. The contraction of the heart-muscle. 



3. The rush of blood into the arteries. 



4. The sudden tension of the ventricular chambers and the 



auriculo-ventricular valves. 



It has already been seen that the heart's impulse is caused by 

 a sudden change in density of the muscle rather than by a knock 

 against the chest. Moreover, the first sound is heard quite readily 

 when the chest wall is removed, so that the apex beating against 

 the thorax cannot even help to cause the sound. 



The sound is not unlike the tone which accompanies the con- 



* A flexible stethoscope to listen to one's own heart sounds can easily be 

 made by fitting to one end of a piece of rubber tubing about 18 inches long 

 the mouth-piece, and to the other end the bowl of a wooden pipe. The 

 bowl is applied over the different regions of the heart, and the mouth-piece 

 firmly fitted in the ear. 



