194 CIECTTLATION 



arterial length. In this way each portion of the artery 

 wall expands to a maximum and then contracts, at inter- 

 vals corresponding to the systolic and diastolic periods 

 of the heart. The disappearance of this wave in the 

 capillaries and veins is explained when we consider how 

 the arteries branch into smaller and smaller tubes, which 

 are farther and farther removed from the seat of pressure 

 until in the capillaries the wave has become so split up as 

 to be barely perceptible, and in the veins is converted into 

 a steady flow. In this respect it is like a water wave, 

 which becomes less apparent the farther we go from the 

 center of the disturbance. It is this wavelike character 

 of the flow of the blood in the arteries that enables us to 

 feel a pulse at points where the arteries are near the sur- 

 face. What we actually count in taking the pulse is the 

 time between successive periods of pressure and relaxa- 

 tion, and since these correspond to expansion and 

 contraction of the heart they enable us to detect the 

 rate of beat of the heart. ' The physician uses the 

 pulse point in the wrists and temples to furnish him 

 with valuable information about the heart and circula- 

 tion. 



Pulse rate. — The rate of the pulse or heart beat is subject to 

 great variation under different conditions of health and disease. 

 It is this fact that makes it a valuable indicator of the body con- 

 dition to the physician. 



Age, sex, size, atmospheric pressure, all have a distinct effect 

 upon the pulse rate. The average rate for the adult man is 

 seventy beats per minute, and for the adult woman seventy-eight 

 to eighty per minute, showing that sex affects the rate. Tall 

 individuals have a slower rate than short persons, while large 

 bodies have a slower rate than small bodies. The human rate is 

 most rapid in infancy, sinks rapidly at first, and then more slowly 



