48 PHYSIOLOGY. 



Work and Rest of the Heart. The time taken by the 

 different parts of the heart beat are about as follows : The 

 auricle contracts about one eighth of the time and rests 

 the other seven eighths. The ventricle contracts about 

 three eighths of the time and dilates during about five 

 eighths. If we suppose the whole period of the heart beat 

 to be twenty-four hours (instead of eight tenths of a sec- 

 ond), we can 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) f 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 ob- 

 servers state that the resting period is even greater than 

 these figures would show. 



Since the contraction of the ventricles immediately fol- 

 lows that of the auricles, one half of the time is occupied 

 by the whole contraction of the heart, 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 suc- 

 cessive impulses that we feel. Suppose a policeman had 

 the power of sleeping at will, and that he slept thirty min- 

 utes of each hour, and that in the remaining 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. This ratio of work and rest is fairly constant in 

 the varying rates of heart beat. 



