THE CIRCULATION OF THE BLOOD 541 



THE HEART SOUNDS 



With a binaural stethoscope auscultate the 

 chest over its entire extent during normal respi- 

 ration and while the subject holds his breath. 



1. Note that two sounds are heard in the 

 heart region. 



2. Determine at what point each of the sounds 

 is most distinct. 



It will be found that one, termed the "first 

 sound," will be most distinct where the ventricle 

 comes nearest the surface, near the apex of the 

 heart, in the space between the fifth and sixth 

 ribs, about 2.5 cm. below and 2.5 cm. within the 

 left nipple. Close inspection of this region in 

 persons not too fat will show that the chest wall 

 is raised at each contraction of the heart. The 

 cardiac impulse, as it is called, may be felt dis- 

 tinctly by one or two fingers laid in the fifth 

 intercostal space. It is caused by the rapid 

 increase in the tension of the ventricle. 



The " second sound " will be heard most dis- 

 tinctly immediately over the aortic arch, near the 

 junction of the second right costal cartilage with 

 the sternum. 



3. Observe the two sounds with relation to 

 their duration, pitch, intensity, and quality. 



