THE HEART-BEAT. 75 



more easily see how much of the time the heart is actually at 

 work, and how much of the time the heart is resting : 



Auricle contracting (working) | of the time 3 h., resting 21 h. 

 Ventricle contracting (working) of the time 9 h., resting 15 h. 



No part of the heart, therefore, is working longer than a 

 man would who only works nine hours a day. Some observers 

 state that the resting period is even greater than these figures 

 would show. 



Since the contraction of the ventricles immediately follows 

 that of the auricles, one-half of the time is occupied by the 

 whole beat of the hsart, and during half the time the whole 

 heart is resting. This is different from our usual statements 

 regarding the work of the heart. We hear it said that the 

 heart never rests. Its work and rest follow each other at such 

 short intervals that we do not appreciate the interval of rest 

 that comes between the successive impulses that we feel. 

 Suppose a policeman had the power of sleeping at will, and 

 that he slept thirty minutes of each hour, and that in the re- 

 maining thirty minutes he made the rounds of a block. If 

 we saw him passing regularly once an hour, every hour of the 

 twenty-four, we might suppose that he did not sleep at all 

 during the entire time. 



The Beat of the Heart. The apex of the heart is al- 

 ways in contact with the chest wall. Consequently, it never 

 strikes it. At each beat it pushes hard against the chest 

 wall. This push may be felt and seen, and is called the 

 heart-beat. 



The Sounds of the Heart. There are two sounds of 

 the heart : 



1. A short, sharp sound made by the closing of the semi- 

 lunar valves. 



2. Just preceding this sound a longer, duller sound may 



