CHAPTER XXIV 

 THE PULSE 



Bv the expulsion of the blood at each systole the walls of the 

 aorta are suddenly distended. From the aorta a wave of distension 

 passes down the walls of the arteries. This wave of distension is 

 called the ' ; pulse." As the pulse is distributed over an ever- widening 

 field its energy is expended in dilating the elastic arteries, and 

 disappears finally in the arterioles. From a wounded artery the blood 

 spurts in pulses, from a wounded vein it flows continuously. By 



FIQ. 113. THE SUSPENSION METHOD OF usrNa THE DUDGEON _SPHYGMOGRAPH. 



(Lewis.) 



feeling two pulses, or, better, by placing tambours on, say, tne 

 carotid and radial arteries, and recording the two pulses synchro- 

 nously, it has been found that the pulse occurs later the farther 

 the seat of observation is away from the heart. The velocity with 

 which the pulse-wave travels down the arteries has been determined 

 thus. It is about 7 to 8 metres per second twenty to thirty times 

 as fast as the blood flow. The wave-length of the pulse is obtained 

 by multiplying the duration of the inflow of blood into the aorta by 

 the velocity of the pulse-wave. It is about 3 metres. 



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