THE HEART AND THE BLOOD VESSELS 153 



backward through the arteries since the heart pump is. con- 

 stantly pushing more blood along into them, thus keep- 

 ing the stream in one direction. Veins, however, which 

 do not feel this impulse from the heart, are provided with 

 valves so that a forward flow alone is possible. 



Diseases of the Circulation. Anything that impairs the 

 circulation will evidently interfere with normal bodily activity. 

 Irregularities in the action of the valves or muscles of the heart 

 will of course interfere with circulation. Slight imperfections 

 in heart action are not uncommon. They are commonly first 

 noticed by a shortness of breath rather than any trouble around 

 the heart. Persons with such defects must live a more quiet life 

 than is necessary for one whose heart is normal, and must avoid 

 all forms of athletics that produce excessive strain or ex- 

 haustion, e.g. running or football. With care in regard to over- 

 strain, these heart weaknesses need not cause especial alarm, 

 and those who have them are likely to live as long and useful 

 lives as others without such weakness. 



In youth all the arteries are strong and elastic and capable 

 of adapting themselves to a large range of needs, so that vigorous 

 exercise, even of long distance running, is well endured. When 

 one passes middle life, however, the arteries become less elastic 

 and less able to respond to unusual demands upon them. When 

 this occurs a person should begin to live a more quiet life and 

 not subject his heart and arteries to such strains as would come 

 from running to catch a train, hurrying up stairs, or other 

 vigorous exercise. Later in life the trouble may become ex- 

 cessive, producing a disease called hardening of the arteries 

 (arterial sclerosis). This is commonly a sign of the approach o? 

 )ld age and for it there is no known remedy. 



