224 



ARTIFICIAL PULSE. 



[BOOK i. 



perhaps still better seen if a number of levers be similarly 

 arranged at different distances from the pump as in Fig. 59. 



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FIG. 59. 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.) 



At each stroke of the pump, each lever rises until it reaches 

 a maximum (Fig. 59, la, 2a, &c.), and then falls again, thus 

 describing a curve. The rise is due to the expansion of the part 

 of the tube under the lever, and the fall is due to that part of the 



