THE HEART AND CIRCULATION. Ill 



beat being increased. When a person faints from a blow 

 in the abdomen, it is because the pneumogastric is 

 affected and inhibits the action of the heart. The work 

 of the heart is very dependent upon its nervous condition 

 and functional diseases of the heart are practically wholly 

 due to nervous derangement. 



Heart Sounds. Through the stethoscope two heart 

 sounds may be heard. They are known as the first and 

 second sounds. The first is a soft, rushing sound, stronger 

 and louder than the other, and is caused in part by the 

 contraction of the muscle itself when the blood is forced 

 out and in part by the closure of the auriculo-ventricular 

 valves. The second sound is shorter and sharper, a snap, 

 and is caused by the closure of the semilunar valves 

 when the contraction of the ventricles ceases and they 

 begin to refill. In certain diseased conditions, where 

 the edges of the valves are roughened, they do not snap 

 properly and the sound varies from the normal. 



The Heart Beat. The rate of the heart beat is propor- 

 tionate to the size of the person and increases in rapidity 

 as the size diminishes. If the ear is placed over the abdo- 

 men of a pregnant woman, the heart of the fetus can be 

 heard beating very rapidly. In prolonged labor it may 

 become more rapid or very faint and warn the doctor 

 that something should be clone. The usual rate of the 

 pulse in the fetus is 140 to 150 times a minute, though it 

 varies with size and sex. At birth it drops to 140 to 130; 

 for the first year it is 130 to 115; for the second year 115 

 to 105; for the third year 105 to 95; from the seventh to 

 the fourteenth years 80 to 90; from the fourteenth to the 

 twenty-first years 75 to 80; from twenty-one to sixty 60 

 to 75. In old age it rises a little and is 75 to 80. The rate 

 is higher in the average woman than in the average man 

 and increases with exercise, with increase of temperature, 

 and in high altitudes, where the atmospheric pressure is 

 less. 



At each beat of the heart from four to six ounces of 

 blood are expelled into the plumonary artery and the 



