162 



THE PULSE. 



[BOOK 



1. With each stroke of the pump, each lever (Fig. 27, L and II.) 

 rises to a maximum, la, 2a, and then falls again, thus describing a 

 curve, the pulse-curve. This shews that the expansion of the 



1 ' 



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FIG. 27. Pulse-curves described by a series of sphygmographic levers placed at 

 intervals of 20 cm. from each other along an elastic tube into which fluid is forced 

 by the sudden stroke of a pump. The pulse- wave is travelling from left to right, as 

 indicated by the arrows over the primary (a) and secondary (b, c) pulse- waves. The 

 dotted vertical lines drawn from the summit of the several primary waves to the 

 tuning-fork curve below, each complete vibration of which occupies ^sec., allow the 

 time to be measured which is taken up by the wave in passing along 20 cm. of the 

 tubing. The waves a are waves reflected from the closed distal end of the tubing ; 

 this is indicated by the direction of the arrows. It will be observed that in the 

 more distant lever VI. the reflected wave, having but a slight distance to travel, 

 becomes fused with the primary wave. (From Marey.) 



tubing passes the point on which the lever rests in the form of 

 a wave. At one moment the lever is quiet: the tube beneath 

 it is simply distended to the normal permanent amount indicative 



