1036 PHYSIOLOGY 



of the tube to distension, since this will determine the rapidity of its 

 recovery. The velocity of propagation of the wave of increased 



FIG. 410. 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 FOSTER, after MAREY.) 



pressure, or the wave of expansion of the artery, is expressed by the 

 following formula : 



= Y Drf 



