CAPILLARIES 



157 



III. Lie down or sit quietly for two or three minutes. Again record the 

 pulse rate. 



A. What is the effect of rest on the heart and arterial muscles ? 



IV. What is the value of the arterial pulse ? 



V. If more blood is needed in one part of the body than in another, how can 

 it be properly distributed ? 



The normal pulse rate in men is seventy-two beats per minute, for women 

 seventy-six. The pulse rate is still higher in children. An abnormal pulse 

 indicates some sort of unusual physiological condition. 



Capillaries. The capillaries are microscopic tubes found 

 among the cells of the tissues. These vessels are characterized 

 by a lack of muscular tis- 

 sue. Their walls are mem- 

 branous. They receive the 

 blood from the arteries 

 and send it to the veins. 

 Materials pass from the 

 blood through the thin 

 walls of the capillaries to 

 the cells in surrounding 

 tissues. The waste prod- 

 ucts in the lungs and 

 other parts of the body 

 pass into the blood from 

 which they are later dis- 

 charged. This inter- 

 change of products is Capillarieg are go t . ny and numeroug that 



possible because of the traverse the most minute parts of the body. The red 



corpuscles pass through in practically single file. 



membranous walls of the 



capillaries. The blood receives enough of an impulse from the 



heart to keep it moving through the capillaries. 



Veins. The veins receive the blood from the capillaries and return 

 it to the heart. The veins connected directly with the capillaries 



