242 THE HUMAN BODY. 



would be felt immediately after each stroke of the pump,, 

 although the liquid pumped in at the other end would have 

 remained about its point of entry; it would cause the pul- 

 sation not by flowing along the tube itself, but by giving a 

 push to the liquid already in it. If instead of absolutely 

 closing the distal end of the tube one brought about a 

 state of things more nearly resembling that found in the 

 arteries by allowing it to empty itself against a resistance, 

 say through a narrow opening, the phenomena observed 

 would not be essentially altered; the increase of pressure 

 would travel along the distended tube far faster than the 

 liquid itself. 



The pulse being dependent on the heart's systole, " feel- 

 ing the pulse 5 ' of course primarily gives a convenient means 

 of counting the rate of beat of that organ. To the skilled 

 touch however it may tell a great deal more, as for example- 

 whether it is a readily compressible or " soft pulse" show- 

 ing a low arterial pressure, or tense and rigid (" a hard 

 pulse") indicative of high arterial pressure, and so on. In 

 adults the normal pulse rate may vary from sixty-five to 

 seventy-five. In the same individual it is faster when 

 standing than when sitting, and when sitting than when 

 lying down. Any exercise increases its rate temporarily 

 and so does excitement; a sick person's pulse should not 

 therefore be felt when he is nervous or excited (as the- 

 physician knows when he tries first to get his patient calm 

 and confident), as it is then difficult to draw correct 

 conclusions from it. In children the pulse is quicker than 

 in adults, and in old age slower than in middle life. 



The Rate of the Blood-Flow. As the vascular system 

 becomes more capacious from the aorta to the capillaries 

 the rate of flow in it becomes proportionately slower, and 

 as the total area of the channels diminishes again from the 

 capillaries to the venae cavse, so does the rate of flow quicken 

 again, just as a river current slackens where it spreads out,, 

 and flows faster where it is confined to a narrower channel; 

 a fact taken advantage of in the construction of Eads' jetties 

 at the mouth of the Mississippi, the object of which is to 

 make the water flow in a narrower channel and so with a 



