THE PULSE 63 



jets from the heart are blended into one continuous 

 stream. The whole force of each blow of the heart is not 

 at once spent in driving a quantity of blood through the 

 capillaries ; a part only is thus spent, the rest goes to 

 distend the elastic arteries. But during the interval 

 between that beat and the next the distended arteries are 

 narrowing again, by virtue of their elasticity, and so are 

 pressing the blood on into the capillaries with as much 

 force as they were themselves distended by the heart. 

 Then comes another beat, and the same process is re- 

 peated. At each stroke the elastic arteries shelter the 

 capillaries from part of the sudden blow, and then quietly 

 and steadily pass on that part of t lie blow to the capillaries 

 during the interval between the strokes. 



The larger the amount of elastic arterial wall thus 

 brought into i)lay, i.e. the greater the distance from the 

 heart, the greater is the fraction of each heart's stroke 

 which is thus converted into a steady elastic pressure 

 between the beats. Thus the pulse becomes less and 

 less marked the farther you go from the heart ; any given 

 length of rhe arterial system, so to speak, being sheltered 

 by the lengths between it and the heart. 



Every inch of the arterial system may, in fact, be con- 

 sidered as converting a small fraction of the heart's jerk 

 into a steady pressure, and when all these fractions are 

 summed up together in the total length of the arterial 

 system no trace of the jerk is left. 



As the immediate, sudden effect of each systole becomes 

 diminished in the smaller vessels by the catlses above 

 mentioned, the influence of this constant pressure becomes 

 more obvious, and gives rise to a steady passage of the 

 fluid from the arteries towards the veins. In this way, in 

 fact, the arteries perform the same functions as the air- 

 reservoir of a fire-engine, which converts the jerking 

 impulse given by the pumps into the steady flow from 

 the nozzle of the delivery hose. 



The phenomena so far described are the direct outcome 



