HEART 



409 



By means of the microphone apphed over the heart, two 

 faint sounds have been recorded during auricular systole, but 

 so far they cannot be considered as of clinical importance. 



Cardiac Murmurs- — When the valves are diseased and fail 

 to act properly, certain continuous sounds called cardiac 

 murmurs are heard. 



These owe their origin to the fact that, while a current of 



Stenq-is' 



• horn 



''liiTRAl. 



koMPET/ 

 EMCE. 



Fig. 176. — To show the Periods in the Cardiac Cycle at which the various 

 Murmurs of Stenosis and Incompetence occur. 



fluid passing along a tube of fairly uniform calibre is not 

 thrown into vibrations and therefore produces no sound, 

 when any marked alterations in the lumen of the tube 

 occurs — either a sudden narrowing or a sudden expansion — 

 the flow of fluid becomes vibratory, and, setting up vibrations 

 in the solid tissues, produces a musical sound. 



